1. INTRODUCTION

Cyanobacteria, historically recognized as blue-green algae, represent one of Earth’s most ancient and ecologically foundational groups of prokaryotes, with a fossil record extending over 2.5 billion years (Komárek et al. 2014;Guiry and Guiry 2023). These oxygenic phototrophs play essential roles in global primary production, nitrogen fixation, and microbial community structuring across aquatic ecosystems (Werner 2010;Cai et al. 2024;Nawaz et al. 2024). Despite their ecological importance and widespread occurrence, the full extent of cyanobacterial diversity and distribution remains poorly resolved in many regions, including South Korea (NIBR 2024).

Taxonomic understanding of cyanobacteria has evolved significantly over the past century. Early classifications by Bornet and Flahault (1886a), Gomont (1892), and Geitler (1925) relied on morphological characters. Since the 1980s, ecological traits, ultrastructure, and molecular phylogenetics have transformed cyanobacterial systematics (Anagnostidis and Komárek 1985;Hoffmann et al. 2005;Komárek et al. 2014). The modern “polyphasic approach” integrates morphological, ecological, and molecular data and supports current databases such as AlgaeBase (Guiry and Guiry 2023). However, morphological taxonomy remains crucial, particularly for field surveys lacking genomic data.

In South Korea, freshwater cyanobacteria studies began with Chung (1968), followed by regional floristic surveys in the 1970s-1990s (Chung 1976, 1993) and expansions by Wui and Kim (1987). These efforts documented over 100 taxa, using Japanese references like Hirose et al. (1977) for identification. From the 2000s onward, research shifted toward bloom-forming genera (Microcystis, Anabaena, Dolichospermum) and their roles in eutrophication (Kim 2013;Song et al. 2022;Wang et al. 2024).

Early studies documented over 100 cyanobacterial taxa in Korea during the 20th century. However, recent floristic investigations continue to reveal previously unknown diversity. For example, Bae et al. (2020) reported Microseira wollei as a previously unrecorded taxon in Korea, and Kim et al. (2022) identified bloomforming cyanobacteria from the Nakdong River Basin. These studies, however, primarily focused on eutrophic reservoirs and bloom scenarios. In contrast, our study expands geographic and ecological coverage to include wetlands, estuaries, and insular systems such as Jeju Island- ecosystems often overlooked in prior surveys.

Recent advances in cyanobacterial taxonomy emphasize the integration of molecular data (e.g., 16S rRNA, ITS, rbcL) with morphology and ecology. The polyphasic framework proposed by Komárek et al. (2014) remains a cornerstone, while the updated classification of cyanobacterial orders and families based on phylogenomic and polyphasic analyses by Strunecký et al. (2023) provides the most current standard for taxonomic consistency. Yet, as of 2024, only 414 cyanobacterial taxa are officially recorded in Korea-representing <8% of the global estimate (~5,300 species; Park 2012a, 2012b;NIBR 2024). This highlights the insufficient taxonomic coverage, particularly in highland streams, floodplain wetlands, and tidal gradients. Considering Korea’s diverse aquatic environments, including alpine rivers and volcanic wetlands, many cyanobacterial species are likely still undocumented.

In response to this knowledge gap, we conducted a nationwide floristic survey between 2017 and 2024 across 43 diverse freshwater and brackish habitats. Species were identified using classical microscopy alongside modern taxonomic literature (e.g., Komárek et al. 2014). The study focused on morphologically distinct taxa absent from the national checklist. In doing so, we aimed to contribute reliable baseline data for biodiversity assessments, ecological monitoring, and predictive modeling of cyanobacterial dynamics.

Therefore, the aim of this study is to systematically document morphologically distinct cyanobacterial taxa previously unrecorded in Korea, and to clarify their taxonomic identity through classical microscopy and authoritative references. This research also seeks to provide baseline data for future floristic, ecological, and molecular studies in diverse Korean aquatic ecosystems.

2. MATERIALS AND METHODS

Cyanobacteria were collected from 43 diverse aquatic habitats across South Korea, including freshwater and brackish environments such as lakes, ponds, swamps, rivers, estuaries, and intertidal flats (Fig. 1), between March 2017 and October 2024. Particular emphasis was placed on underexplored ecosystems, including tidal marshes, estuarine transition zones, and insular regions like Ganghwa Island (Incheon) and Jeju Island.

Phytoplankton samples were obtained using conical plankton nets (mesh size 10-20 μm) through horizontal tows or vertical hauls, depending on site depth. Epilithic and epiphytic cyanobacteria were collected by gently brushing submerged stones, woody debris, and macrophyte surfaces using soft-bristled brushes or forceps. Each sample was divided into two parts. One was preserved in 0.5% Lugol’s iodine solution, and the other was stored fresh under chilled conditions for immediate microscopic examination.

For microscopy, temporary wet mounts and permanent slides were prepared. Permanent mounts were embedded in glycerol jelly (Sigma-Aldrich^®, USA), sealed with transparent nail polish (The Cashop^®, Korea), and covered with standard cover slips. Microscopic observations were conducted using Carl Zeiss Axioskop 20 and Axio Imager A2 microscopes, at magnifications ranging from 200× to 1,000×. Representative micrographs were captured using a Zeiss Axiocam HRc digital imaging system. Morphological identification was based on key diagnostic characters, including trichome configuration, presence and morphology of heterocytes, sheath characteristics, apical cell structure, intracellular granules and reproductive modes.

Identification followed both classical and recent taxonomic literature. Notably, the Algal Flora of Korea Volumes 5-1 and 5-2 (Park 2012a, 2012b), Komárek et al. (2014), Geitler (1932), and recent Korean floristic updates (Kim et al. 2022;Song et al. 2022;Wang et al. 2024) were utilized as key references. Previously recorded taxa were cross-verified using voucher specimens and distributional records documented in national survey reports published by the National Institute of Biological Resources (NIBR 2017) and the Nakdonggang National Institute of Biological Resources (NNIBR 2017, 2018). Taxa that did not correspond to existing Korean records were subjected to detailed morpho-taxonomic evaluation and illustration.

In situ environmental variables-including water temperature (°C), pH, electrical conductivity (EC, μS cm^-1), and salinity (psu)-were measured using a portable multi-probe (U-50; Horiba, Japan). However, measurements were hindered in several wetland and tidal sites due to field constraints such as shallow water depth, dense vegetation or stagnant flow. Consequently, water quality parameters were not uniformly obtained across all stations. Where available, such physicochemical data were used to interpret the ecological preferences and habitat specificity of newly identified taxa.

All newly observed species were documented through direct microscopic observation. Diagnostic traits were recorded using digital photomicrographs, while preliminary line drawings were prepared for internal comparison but are not included in this manuscript to avoid confusion. Species presence-absence and habitat metadata were tabulated and georeferenced. Sampling site locations are illustrated in Figure 1, and the ecological characteristics of the eight stations where newly recorded taxa were found are summarized in Table 1 (note that the table is restricted to occurrence sites of unrecorded taxa, not all 43 surveyed habitats). A concise overview of diagnostic morphological traits and their occurrence sites for all 18 newly documented taxa is presented in Table 2, complementing the detailed species descriptions and figures (Figs. 2-4).

3. RESULTS

3.1. Overview of newly observed cyanobacterial taxa in Korean lentic ecosystems

From March 2017 to October 2024, systematic field investigations were conducted at 43 sampling sites across South Korea. These sites included diverse freshwater and brackish habitats such as lakes, ponds, wetlands, streams, reservoirs, estuarine areas and paddy fields. During this period, we catalogued over 600 algal taxa. In 2017 alone, 25 cyanobacterial species were identified from freshwater sites, and an additional 65 species were documented from brackish waters. In 2018, a further 21 freshwater species were submitted to the National Institute of Biological Resources (NIBR) and the Nakdonggang National Institute of Biological Resources (NNIBR) for deposition and reference.

Detailed morphological examinations and comparisons with authoritative taxonomic references (e.g., Joosten 2006;Komárek 2013, 2014;Guiry and Guiry 2023) resulted in the identification of 18 previously unreported cyanobacterial species in Korea. These taxa span across multiple orders, including Gomontiellales, Nodosilineales, Synechococcales, Nostocales, and Stigonematales, as classified under the contemporary framework proposed by Komárek (2014) and cross-validated with recent entries in AlgaeBase (Guiry and Guiry 2023).

The newly documented 18 taxa include: Gomphosphaeria aponina, Cyanothece aeruginosa, Hydrocoryne spongiosa, Lemmermanniella parva, Woronichinia pusilla, Dolichospermum compactum, Microcystis botrys, Calothrix brevissima, Nostoc carneum, Wollea saccata, Merismopedia minutissima, Woronichinia obtusa, Gloeotrichia aurantiaca, Gloeotrichia intermedia, Gloeotrichia kamtschatica, Gloeotrichia pisum, Scytonema ocellatum and Stigonema minutum.

These newly documented taxa display diverse morphological characteristics and occupy various ecological niches, including unicellular, colonial, filamentous, and mat-forming types (Komárek and Anagnostidis 1998;Komárek 2013;Strunecký et al. 2023). Many species produce distinctive mucilage envelopes or possess specialized structures such as heterocytes or akinetes, which are crucial for nitrogen fixation and survival under adverse conditions (Joosten 2006;Komárek 2013;Huisman et al. 2018). For instance, Cyanothece aeruginosa was identified as a thick-mucilage, diazotrophic unicellular planktonic species, while Dolichospermum compactum exhibited bloom-forming potential through its tightly coiled, compact filamentous morphology (Wacklin et al. 2009;Komárek 2013;Li et al. 2013). Hydrocoryne spongiosa displayed a sponge-like filamentous structure that is rarely reported in the literature (Hoffmann et al. 2005;Komárek 2013).

One taxonomically notable case is Woronichinia pusilla, whose nomenclatural history reflects several generic reassignments-from Coelosphaerium to Gomphosphaeria, Coelomoron and finally Woronichinia, as per the latest consensus in AlgaeBase (Guiry and Guiry 2023). The defining features-radial arrangement of peripheral cells, compact mucilage envelope, and lack of stalks-were consistent with its classification under Woronichinia.

Ecologically, the newly observed species were collected from diverse aquatic environments, including nutrient-rich reservoirs (e.g., St. 5, Sori Reservoir), urban ponds (e.g., St. 2, Songchu Wetland) and brackish estuarine systems (e.g., St. 7, Geum River). Certain taxa, including Microcystis botrys and Gloeotrichia aurantiaca, have the potential to form harmful algal blooms (HABs) or serve as bioindicators of eutrophication.

A summary of the sampling stations, ecological context and key morphological features for each taxon is provided in Table 1, which has been updated to include the corresponding Order (taxonomic level) for each species. These findings not only expand the floristic inventory of cyanobacteria in Korea but also highlight the ecological variability and adaptation strategies of cyanobacterial species in lentic and transitional aquatic systems. Note that the order of species listed in Table 1 follows the sequence of species descriptions presented in Section 3.2 of the Results. Sites such as Monmulgak Wetland (St. 8), where multiple taxa were recorded, represent ecological hotspots of cyanobacterial diversity.

In summary, the newly documented taxa were predominantly found in lentic and transitional habitats, including reservoirs, urban ponds and brackish wetlands. Notably, Jeju Island’s Monmulgak Wetland emerged as a biodiversity hotspot, hosting multiple novel taxa such as Gloeotrichia aurantiaca, Stigonema minutum and Scytonema ocellatum. These findings suggest that such insular and peripheral habitats may harbor cryptic cyanobacterial diversity overlooked in conventional surveys.

3.2. Morphological descriptions and ecological observations of newly recorded species

This section includes detailed taxonomic descriptions, microscopic observations, environmental data (e.g., water temperature, pH, electrical conductivity), and ecological remarks for each of the 18 newly recorded taxa. Key diagnostic features, including colony formation, cell shape, sheath and mucilage characteristics and reproductive structures (e.g., akinetes, heterocytes) are emphasized to clarify taxonomic distinctions. Each species description references authoritative literature (e.g., Huber-Pestalozzi 1938; Joosten 2006; McGregor et al. 2007; Komárek 2013) with discussions about their potential roles as bioindicators or bloom-forming species, where applicable. The order of taxa presented below follows the modern cyanobacterial classification system proposed by Komárek (2013, 2014) arranged by taxonomic hierarchy: Chroococcales, Synechococcales, Nostocales and Stigonematales. This phylogenetic arrangement ensures consistency with contemporary taxonomy and facilitates comparative interpretation among related genera.

Class Cyanophyceae

Order Chroococcales

Family Gomphosphaeriaceae

Genus GomphosphaeriaKützing, 1836

1. Gomphosphaeria aponinaKützing, 1836 (Fig. 2A, B)

Synonyms. None reported.

References.Kützing (1836);Geitler (1925); Huber- Pestalozzi (1938); Desikachary (1959);Prescott (1962);Hirose et al. (1977);Komárek and Hindák (1998, p. 222, fig. 13-1); Komárek and Anagnostidis (2008, p. 221, fig. 290); Dwivedi et al. (2010).

Description. Colonies are spherical to ovoid and occasionally form composite aggregations composed of 2-4 cells, which are either tightly clustered or loosely dispersed (see Fig. 2A, B). These cells are embedded in a thick, colorless mucilaginous matrix. Transparent and relatively thick mucilaginous stalks radiate from the colony’s center in a pinnate branching pattern, terminating in individual cells. The cells are oval to club shaped, occasionally reniform during division, and exhibit pale blue-green, olive-green or yellowish hues. Cells range from 7-12 μm in length and 3-6.5 μm in width. Within Gomphosphaeria, this taxon is characterized by a conspicuous central mucilage core with pinnately radiating stalks that terminate in single peripheral cells (Fig. 2A, B), and by the frequent occurrence of reniform cells during division. In contrast, congeners such as G. natans commonly show less conspicuous central radiating stalks and a more diffuse distribution of cells within the mucilage. Superficially similar colonial genera (e.g., Coelosphaerium, Snowella, Woronichinia) lack this combination of a dense central mucilage core plus thick, radiating stalks ending in single cells.

Occurrence and Ecology. This species was collected in June 2022 from Lake Cheongna, Incheon-si, a lentic freshwater body with slightly elevated salinity. At the time of sampling, water temperature was 26.0°C, pH was 9.4, electrical conductivity measured 3,030 μS cm^-1, and salinity was 1.6 PSU. The species typically occurs in freshwater to brackish ponds, lakes and wetlands of temperate regions, often coexisting with other algae or macrophytes.

Sampling Site. Cheongna Reservoir, Incheon (St. 1; 37°32ʹ26ʺN, 126°38ʹ00ʺE).

Voucher Specimen. DAEJIN-20220617.

Remarks.Gomphosphaeria aponina was first described by Kützing (1836) as the type species of the genus, though without accompanying illustrations. Subsequent authors, including Geitler (1925) and Huber- Pestalozzi (1938), expanded upon this by describing oval to reniform cells and mucilaginous stalks radiating from a central core. Komárek and Hindák (1998) further refined the genus by distinguishing it from morphologically similar genera (Coelosphaerium, Snowella, Woronichinia) based on colony structure, the presence of central stalks, and mucilage differentiation. Our Korean material conforms to these diagnostic features in colony architecture and cell morphology, supporting a provisional record of G. aponina for Korean freshwater systems.

Family Microcystaceae

Genus MerismopediaMeyen, 1839

2. Merismopedia minutissimaJoosten, 2006 (Fig. 2C, D)

Synonyms. None reported.

References.Joosten, A.M.T. (2006). Flora of the Blue- Green Algae of the Netherlands I: The Non-Filamentous Species of Inland Waters. KNNV Publishing, Utrecht. p. 101, Fig. 43a-e. Also see: Geitler (1925);Desikachary (1959);Prescott (1962);Hirose et al. (1977);Yamagishi and Akiyama (1987);Komárek and Anagnostidis (1986, 2008).

Description. Colonies are free-floating and embedded within a thick, transparent mucilage (see Fig. 2C, D). They typically contain 16-64 densely packed cells, although larger colonies comprising over 1,000 cells are sometimes observed. Colonies appear rectangular or slightly curved and often fragment into smaller subunits. Cells are arranged in a geometrically regular pattern with intercellular distances ranging from 0.2 to 1.7 μm. Cell shape varies from rectangular to hemispherical or ovoid, with rounded corners and dark bluegreen to greyish coloration. Each cell is completely surrounded by mucilaginous material. Cells range from 0.6-1.9 μm in length and 0.5-1.3 μm in width. Within Merismopedia, this species is characterized by very small cell size (<~2 μm), tight intercellular spacing, and compact, plate-like colonies embedded in dense mucilage (Fig. 2C, D). In contrast, congeners such as M. minima and M. tenuissima commonly exhibit relatively larger or more variably spaced cells and more readily disaggregating colonies, while M. convoluta tends to show less regular plate organization.

Occurrence and Ecology. This species was collected in July 2022 from a slow-flowing freshwater river segment in the mid-reach of the Geum River. Environmental parameters at the time of sampling included: water temperature 29.0°C, pH 8.2, electrical conductivity 312 μS cm^-1, and salinity 0 PSU. The species is typical of eutrophic, temperate freshwater lakes, ponds, and wetlands with relatively high conductivity (Joosten 2006).

Sampling Site. Baekmagang Bridge, Chungcheongnam- do (St. 7; 36°18ʹ15ʺN, 126°55ʹ18ʺE).

Voucher Specimen. DAEJIN-20220726.

Remarks. The genus Merismopedia was established by Meyen (1839) with M. punctata as the type species. Since then, over 30 species have been described, including common taxa such as M. convoluta, M. smithii and M. elegans, which are frequently reported as planktonic or metaphyton in meso- to eutrophic freshwater bodies (Geitler 1925;Desikachary 1959;Joosten 2006). In Korea, small-celled colonies have often been misidentified as M. minima, M. tenuissima or even M. convoluta, lead ing to taxonomic confusion. However, Joosten (2006) clarified that M. minutissima-with its very small cells, dense mucilage, and compact colony form-is a distinct freshwater species, ecologically and morphologically separate from marine or easily disaggregating taxa such as M. warminigiana. LM figures (Fig. 2C, D) indicate the diagnostic combination of i) densely packed, very small cells, (ii) regular plate-like colony architecture, and (iii) uniformly thick mucilage, which together distinguish M. minutissima from the aforementioned congeners. Korean material conforms to these diagnostic characters, supporting a provisional record of M. minutissima in inland waters of Korea.

Genus Microcystis Lemmermann, 1907

3. Microcystis botrys Teiling, 1942 (Fig. 2E)

Synonyms. None reported.

References. Teiling (1942); Komárek (1996); Komárek and Anagnostidis (1998); Hindák (2001, 2006); Cronberg and Baalen (2004); Joosten (2006, p. 172, fig. 80).

Description. Colonies are free-floating and composed of densely aggregated cells that organize into multiple distinct subcolonies (see Fig. 2E). These subcolonies are typically spherical, ovoid or reniform in shape. Each subcolony is surrounded by a conspicuous, broad mucilaginous envelope that often contains dissolved cellular debris. In some cases, colonies exhibit faint radial arrangements. The mucilage boundary is not sharply defined, often appearing diffuse. Individual cells are dark blue-green, spherical, and contain prominent gas vesicles. Cell diameters range from 4-7 μm. Colonies comprise multiple botryoidal subcolonies embedded within a common, thick mucilage; the mucilage margin appears smooth to slightly lobate under LM, and intersubcolony spaces are visible without staining.

Occurrence and Ecology.Microcystis botrys occurs in temperate freshwater to slightly brackish environments, including lakes, ponds and wetlands. It is especially common in Central Europe but has a broader global distribution. The species typically inhabits eutrophic waters with high electrical conductivity and blooms during warmer months. In Korea, it was collected in July 2022 from two sites: Gwangri Reservoir 2 in Hongseong- gun, Chungcheongnam-do (no environmental data recorded); while Changnyeong Haman Weir, where water temperature was 29.5°C, pH was 8.0, and conductivity measured 309 μS cm^-1 (According to individual data).

Sampling Site. Gwangri 2 Reservoir, Hongseong-gun, Chungcheongnam-do (St. 5; 36°35ʹ42ʺN, 126°30ʹ07ʺE).

Voucher Specimen. DAEJIN-20220713.

Remarks. During bloom events, M. botrys may resemble altered forms of M. novacekii or M. aeruginosa at early or senescent stages owing to the presence of botryoidal subcolonies in a shared mucilage. It is differentiated by (i) a broad, indistinctly delimited common mucilage, (ii) sharply delineated botryoidal subcolonies embedded within that matrix, and (iii) colony size and margin architecture (Komárek 1996; Komárek and Anagnostidis 1998; Hindák 2006; Joosten 2006). It may also be confused with M. flos-aquae, which typically exhibits a narrower, more uniform mucilage with crisper outer edges and subcolonies that gradually separate while retaining their own mucilage envelopes. In contrast, M. botrys often shows faintly radiating, broad hemispherical to tubular protrusions of the common mucilage, and may contain short embedded filaments of filamentous cyanobacteria (e.g., Pseudanabaena mucicola) (Hindák 2001, 2006). LM figures indicate mucilage boundaries and subcolony partitions with arrows. Taken together, these characters support a provisional record of M. botrys in Korean inland waters; sequence data (e.g., 16S/ITS) would provide additional corroboration.

Order Synechococcales

Family Merismopediaceae

Genus Woronichinia Elenkin, 1933

4. Woronichinia obtusaJoosten, 2006 (Fig. 2F, G)

Synonyms. None reported.

References.Joosten, A.M.T. (2006). Flora of the Blue- Green Algae of the Netherlands I: The Non-Filamentous Species of Inland Waters. KNNV Publishing, Utrecht, p. 131, Fig. 63.; See also: Komárek (1984); Komárek and Hindák (1988);Komárek and Anagnostidis (1998);Joosten (2006);Komárek and Johansen (2015); Nowicka- Krawczyk and Żelazna-Wieczorek (2017); Strunecký et al. (2023); AlgaeBase (2023).

Description. Colonies are solitary and free-floating, enveloped in a colorless mucilaginous matrix with a diameter ranging from 30 to 80 μm (see Fig. 2F, G). During early stages, colonies are spherical, ellipsoidal or kidney-shaped. Occasionally, 2 to 6 subcolonies of uniform or varying size may coalesce into larger composite colonies. Cells are arranged radially in a single, evenly spaced peripheral layer, with relatively loose packing. Individual cells are dark green to bluish and ovate to cuneate with broadly rounded ends, measuring 2.5-4.5 μm in length and 2.0-4.0 μm in width. Within Woronichinia, the combination of a single peripheral monolayer of radially oriented cells and the absence of conspicuous central radiating stalks is diagnostic for W. obtusa; congeners more typically show denser peripheral packing or differing cell outlines. Superficially similar colonial genera can be separated by stalk morphology and colony architecture: Gomphosphaeria commonly possesses a central mucilage core with radiating stalks terminating in single cells, whereas Coelosphaerium lacks stalks and forms more homogeneous spherical colonies; Coelomoron often bears fine stalks with radial-peripheral alignment; Snowella differs in colony organization and cell arrangement.

Occurrence and Ecology. This species is typically found in eutrophic lakes and ponds (Joosten 2006; Nowicka-Krawczyk and Żelazna-Wieczorek 2017). In the present study, W. obtusa was recorded in July 2022 from two locations in Korea: Baekmagang Bridge on the Geum River (WT 29.0°C, pH 8.2, EC 312 μS cm^-1, salinity 0 PSU), and Ganwolho Reservoir in Seosan-si.

Sampling Site. Baekmagang Bridge, Geumgang River, Chungcheongnam-do (St.7; 36°18ʹ15ʺN, 126°55ʹ18ʺE).

Voucher Specimen. DAEJIN-20220726.

Remarks. The genus Woronichinia was established by Elenkin (1933) with W. naegeliana as the type species and was subsequently reclassified among Merismopediaceae (Gomphosphaerioideae) (Komárek 1984; Komárek and Hindák 1988;Komárek and Anagnostidis 1998). Komárek et al. (2014) and Komárek and Johansen (2015) transferred the genus to Coelosphaeriaceae based on phylogenetic and ultrastructural evidence, and Strunecký et al. (2023) later argued for placement within Microcystaceae under a polyphasic framework. LM figures (Fig. 2F, G) highlight diagnostic characters that align with W. obtusa: (i) a radially arranged single peripheral cell layer, (ii) lack of thick, centrally radiating stalks, and (iii) ovate to cuneate cells with broadly rounded ends. Korean material conforms to these features, supporting a provisional record of W. obtusa in Korean inland waters.

5. Woronichinia pusilla (Goor) Joosten, 2006 (Fig. 2H, I)

Synonyms.Coelomoron pusillum, Coelosphaerium pusillum, Gomphosphaeria pusilla.

References.Joosten, A.M.T. (2006). Flora of the Blue- Green Algae of the Netherlands II: The Filamentous Species of Inland Waters. KNNV Publishing, p. 128, Fig. 60.

Description. Colonies are free-floating and enveloped in a colorless mucilaginous sheath, with a diameter ranging from 6 to 30 μm (see Fig. 2H, I). Cells are radially arranged in a single peripheral layer, occasionally overlapping and spaced regularly. The mucilage is homogeneous and lacks any visible radiating pattern or stalks, even when stained with methylene blue or other dyes. Cells are bluish to pale yellow, ovoid to nearly spherical, and measure 1.8-3.2 μm in length and 1.5-3.2 μm in width. Within Woronichinia, this taxon is characterized by a small colony size (≈6-30 μm), a single, densely arranged peripheral monolayer, and the consistent absence of radiating stalks in stained preparations. Congeners such as W. obtusa commonly form larger colonies (often >30 μm) with relatively looser peripheral packing and broader cell outlines, whereas superficially similar colonial genera are separable by stalk/ architecture: Gomphosphaeria bears a central mucilage core with radiating stalks terminating in single cells, Coelosphaerium lacks stalks but forms more homogeneous spherical colonies, and Coelomoron frequently shows fine stalks with radial-peripheral alignment.

Occurrence and Ecology. This species has been reported in eutrophic freshwater environments such as lakes, ponds, and artificial reservoirs. In the present study, it was found in July at a site with the following environmental parameters: water temperature 29.0°C, pH 8.2, electrical conductivity 312 μS cm^-1, and salinity 0 PSU.

Sampling Site. Ganwol Lake, Chungcheongnam-do (St. 4; 36°36ʹ04ʺN, 126°26ʹ24ʺE).

Voucher Specimen. DAEJIN-20220713.

Remarks.Woronichinia pusilla closely resembles Coelosphaerium lacustris in colony habit. However, it can be differentiated by more densely packed peripheral cells, juvenile subcolonies of ≈8-16 cells, and the absence of internal cells within colonies; no stalks are observed even after staining. Originally described as Coelosphaerium pusillum by Van Goor (1924), the species under went several recombinations, including Gomphosphaeria pusilla (Komárek 1956) and Coelomoron pusillum (Komárek 1989). Joosten (2006) reassigned the taxon to Woronichinia pusilla based on Dutch material. Algae Base (2023) treats W. pusilla as a synonym of Coelomoron pusillum, indicating unresolved taxonomy; pending molecular/phylogenetic clarification, the identification here follows the morphological concept of Woronichinia. The observed combination of small colony size, single peripheral monolayer, dense peripheral packing, and lack of stalks supports a provisional record of W. pusilla in Korean inland waters.

Order Gomontiellales

Family Cyanothecaceae

Genus Cyanothece Komárek, 1976

6. Cyanothece aeruginosa (Nägeli) Komárek, 1976 (Fig. 2J-L)

Synonyms.Synechococcus aeruginosus Nägeli.

References.Umezaki, I. & Watanabe, M. (1994). Enumeration of the Cyanophyta (blue-green algae) of Japan: 1. Chroococcales and Oscillatoriales. Japanese Journal of Phycology (Sôrui), 42, 175-219.; Komárek and Anagnostidis (2008), p. 49, fig. 28.

Description.Cyanothece aeruginosa occurs as solitary, free-floating cells enveloped by a thin, often indistinct mucilaginous sheath (see Fig. 2J-L). The cells are broadly oval to short-cylindrical with smoothly rounded ends; pigmentation ranges from dark blue-green to yellow-green. Under high magnification, the cytoplasm frequently appears reticulate/granulate. Cell size varies widely, 10-50 μm×10-30 μm, reflecting physiological variability across developmental stages. Within Cyanohece, this taxon is distinguished by large solitary cells with a thin, continuous mucilage sheath and reticulate chromoplasm; in contrast, superficially similar unicellular/ colonial genera are separable as follows: Aphanothece forms plate-like colonies with multiple cells embedded in a common mucilage; Chroococcus typically occurs as paired (diplococcal) cells with layered mucilage; Microcystis forms macroscopic colonies with gasvesiculate cells; and Synechococcus comprises narrow rods (commonly <3-5 μm wide) lacking a conspicuous mucilaginous envelope.

Occurrence and Ecology. This species was observed in June 2021 at a eutrophic urban wetland characterized by high productivity, slow water movement and elevated levels of dissolved organic carbon.

Sampling Site. Songchu Uldae Wetland, Gyeonggi-do (St. 2; 37°42ʹ36ʺN, 126°58ʹ55ʺE).

Voucher Specimen. DAEJIN-20210614.

Remarks.Cyanothece aeruginosa is a morphologically distinctive planktonic cyanobacterium characterized by large solitary cells, rounded apices and a mucilagebound cell envelope with reticulate thylakoid/chromoplasm appearance. It typically inhabits stagnant or slowmoving, highly eutrophic freshwaters (urban wetlands, backwater zones enriched with dissolved organic matter). The species was originally described as Synechococcus aeruginosus by Nägeli and transferred to Cyanothece by Komárek (1976), with subsequent treatments in Komárek and Anagnostidis (2008). Cyclic nitrogen metabolism has been reported for Cyanothece spp., with temporal separation of photosynthesis and nitrogen fixation (e.g., Stöckel et al. 2008;Welsh et al. 2008), consistent with diazotrophic ecology. In Korea, the taxon is already listed in the national checklist (e.g., NIBR 2024); accordingly, the present material is documented as an ecological occurrence and morphological confirmation, not as a new national record. The observed character set-large solitary cells with thin, continuous mucilage and reticulate cytoplasmic texture-matches published diagnoses and supports the identification of C. aeruginosa in the surveyed site.

Order Nodosilineales

Family Cymatolegaceae

Genus Lemmermanniella Geitler, 1942

7. Lemmermanniella parvaHindák, 1985 (Fig. 2M, N)

Synonyms.Lemmermanniella parvaHindák, 1985: p. 398, fig. 3.

References.Hindák, F. (1985). The cyanophycean genus Lemmermanniella Geitler 1942. Archiv für Hydrobiologie, Supplement 71(3) (Algological Studies 40): 393-401; Joosten, M.T. (2006). Phytoplankton in Lakes and Reservoirs: Composition, Succession and Diversity. KNNV Publishing. p. 49, fig. 12.

Description. This species forms free-floating colonies that are typically small to medium in size, ranging from 18-180 μm in diameter, with spherical to ellipsoidal shapes (see Fig. 2M, N). Cells are arranged in a single compact layer along the periphery of the colony, while the interior hosts sparsely distributed, irregular cells. Colonies are embedded in a transparent, colorless mucilage layer that remains tightly bound to the outer cells. Individual cells are pale blue-green, broadly ovoid to short cylindrical in shape and extremely small, measuring 0.9-2.2 μm in length and 0.6-1.0 μm in width. Within Lemmermanniella, this taxon is characterized by a compact peripheral monolayer combined with sparse, irregularly scattered inner cells and the absence of gas vesicles or radial symmetry. Superficially similar colonial genera are separable by colony architecture and stalk/gas-vesicle traits: Merismopedia forms two-dimensional plates with regularly arrayed cells; Woronichinia typically shows a single peripheral cell layer without internal cells; Coelosphaerium lacks stalks and exhibits a more homogeneous internal distribution; Gomphosphaeria bears a central mucilage core with radiating stalks terminating in single cells; Snowella often contains gas vesicles and more pronounced radial patterns. Occurrence and Ecology. Observed in Ganwolho Reservoir (Seosan-si, Chungcheongnam-do, Republic of Korea) during summer sampling in June 2022. The water body is eutrophic, slow-flowing and nutrientenriched, typical of artificial impoundments subjected to anthropogenic input.

Sampling Site. Ganwolho Reservoir, Seosan-si, Chungcheongnam- do (St. 4; 36°36ʹ04ʺN, 126°26ʹ24ʺE).

Voucher Specimen. DAEJIN-20220614.

Remarks.Lemmermanniella parva is a minute coccoid cyanobacterium distinguished by very small cells, a tightly organized peripheral layer and the lack of gas vesicles. Originally described by Hindák (1985) from Central European waters, it is associated with lentic, nutrient-rich environments. Joosten (2006) recorded L. parva from Dutch reservoirs under thermal stratification and eutrophic conditions, comparable to the Korean site. LM figures (Fig. 2M, N) indicate the diagnostic combination of (i) compact peripheral monolayer, (ii) sparse and irregular inner cells, and (iii) absence of gas vesicles or radial symmetry, which together distinguish L. parva from morphologically similar colonial taxa noted above. Korean material conforms to these characters, supporting a provisional record of L. parva in Korean inland waters.

Order Nostocales

Family Aphanizomenonaceae

Genus DolichospermumWacklin, Hoffmann & Komárek, 2009

8. Dolichospermum compactum (Nygaard) P. Wacklin, L. Hoffmann & J. Komárek, 2009 (Fig. 2O, P)

Synonyms.Anabaena compacta Nygaard.

References.Komárek (2013), p. 702, fig. 865; Wacklin, P., Hoffmann, L., & Komárek, J. (2009). Nostocales (Cyanoprokaryota). In: Süsswasserflora von Mitteleuropa, Bd. 19/2. Elsevier, München; AlgaeBase (2023).

Description.Dolichospermum compactum forms dense, coiled trichomes that are free-floating and typically occur as solitary filaments (see Fig. 2O, P). Trichomes exhibit a tightly coiled, regular helix (≈20-30 turns), with helical diameter 11-16 μm and pitch 4-12 μm; trichome width remains relatively constant along the axis. Cells are near-spherical, blue-green to dark green (gas vesicles present), 3-6 μm in diameter. Heterocytes are intercalary (≈ 5.5-6 μm). Akinetes were not observed in the examined material; literature reports describe spherical to ovoid akinetes (≈8-12.5×7-11 μm) occurring singly or in short series. LM figures annotate coil diameter/ pitch and intercalary heterocytes with arrows; an inset highlights the compact, regular helical pattern. Occurrence and Ecology. Detected in July 2022 at a lentic eutrophic pond (Sori Reservoir) in Hongseonggun, Chungcheongnam-do, Republic of Korea. The site is characterised by shallow, stagnant water and elevated nutrient conditions-favouring bloom-forming cyanobacteria.

Sampling Site. Sori 2 Reservoir, Hongseong-gun, Chungcheongnam- do (St. 5; 36°35ʹ42ʺN, 126°30ʹ07ʺE).

Voucher Specimen. DAEJIN-20220713.

Remarks. Within Dolichospermum, the diagnostic combination of (i) tightly and regularly coiled, compact helices, (ii) relatively uniform trichome width, and (iii) intercalary heterocytes separates D. compactum from congeners. In particular, D. flos-aquae typically shows looser, less regular coils and more variable filament width, while broader-coiled taxa (e.g., D. circinale sensu lato) differ in coil geometry and colony habit. Korean material matches the circumscription of Komárek (2013) in coil number/density and trichome uniformity; however, identification is treated as a provisional record pending molecular corroboration (e.g., 16S/ITS). The absence of akinetes likely reflects vegetative growth stage at sampling rather than a taxon-level trait.

Family Gloeotrichiaceae

Genus GloeotrichiaBornet & Flahault, 1886

9. Gloeotrichia aurantiaca Komárek et al., 2013 (Fig. 2Q, R)

References.Komárek (2013): p. 365, fig. 428; Komárek, J. (2013). Cyanoprokaryota 3. Teil/3rd Part: Heterocytous Genera. Süsswasserflora von Mitteleuropa. Springer Spektrum.

Description. Colonies are microscopic to macroscopic (up to >1 mm), roughly spherical, and epiphytic on aquatic plants (see Fig. 2Q, R). Trichomes are radially arranged from a common center and embedded in a colourless, gelatinous matrix that flows slightly and forms a diffuse outer envelope. Free-floating trichomes are rarely observed. The gelatinous sheath reaches more than 38 μm in thickness and consists of concentric layers- an inner orange-brown zone and an outer, often funnel-shaped or partially enclosed transparent layer. Individual trichomes are short, tapering rapidly toward the apical end, and composed of barrel-shaped cells with constricted cross-walls. Terminal cells are narrowly pointed. Heterocytes are located either at the trichome base or intercalated between akinetes, cylindrical to oval (9-12×7-9 μm), and colourless. Akinetes are long, ovoid, greyish, and arranged in single rows (2-6 cells), often separated by degraded heterocytes or dead cells; they measure 15-48 μm in length. Within Gloeotrichia, this species is distinguished by the persistent, stratified sheath with a diagnostic orange-brown inner layer, short and rapidly tapering trichomes with narrowly pointed terminal cells, and heterocytes positioned basally or intercalary adjacent to rows of akinetes. In contrast, congeners such as G. natans, G. intermedia, G. kamtschatica and G. pisum typically lack the same combination of persistent sheath stratification and trichome/heterocyte placement observed here, or show longer trichomes with different sheath texture.

Occurrence and Ecology. Observed epiphytically on submerged macrophytes in a shallow, slightly acidic to neutral wetland (Monmulgak Wetland), Jeju-si, Republic of Korea. Although the species has been previously reported from alkaline submerged wetlands, the current finding broadens its habitat preference.

Sampling Site. Monmulgak Wetland, Jeju-si (St. 8; 33° 31ʹ06ʺN, 126°42ʹ55ʺE).

Voucher Specimen. DAEJIN-20201015.

Remarks.Gloeotrichia aurantiaca is a heterocytous cyanobacterium characterized by radial colony architecture, stratified mucilage with an orange-brown inner layer, and akinetes near a basal or intercalary heterocyte. The genus Gloeotrichia typically forms benthicepiphytic colonies in soft-water lakes and wetlands. Differential diagnosis from G. natans and allied taxa rests on the persistent, colored inner sheath layer and the arrangement of heterocytes and akinetes, together with short, rapidly tapering trichomes. Komárek (2013) separated G. aurantiaca from related taxa on sheath stratification/color and colony compactness, in addition to ecological tendencies. LM figures (Figs. 2Q, R) highlight the diagnostic combination of (i) a stratified sheath with an orange-brown inner zone, (ii) short, rapidly tapering trichomes with narrowly pointed terminal cells, and (iii) heterocytes positioned basally or intercalary adjacent to rows of akinetes. Given the known morphological similarity among Gloeotrichia species, molecular corroboration (e.g., 16S, rbcL, ITS) is desirable; accordingly, the present material is documented as a provisional record of G. aurantiaca in Korea.

10. Gloeotrichia intermedia (Lemmermann) Geitler, 1925 (Fig. 3A, B)

Synonyms.Rivularia intermedia Lemmermann 1907; Gloeotrichia natans var. intermedia (Lemmermann) Elenkin 1938 (Sources: Komárek 2013; AlgaeBase 2023). References. Komárek, J. (2013). Cyanoprokaryota 3. Teil: Heterocytous Genera. Süsswasserflora von Mitteleuropa, Vol. 19/3. Springer Spektrum, Heidelberg. p. 361, fig. 424. Lemmermann, E. (1907). Die planktonischen Algen. Botanische Ergebnisse der Plankton-Expedition der Humboldt-Stiftung, 2(1): 1-55. AlgaeBase (2023). Gloeotrichia intermedia.

Description. Colonies are large (3-7 mm in diameter), loosely spherical to irregular in shape, brownish in colour, and fragile in structure (see Fig. 3A, B). The colony matrix is composed of trichomes radially arranged from a central point, embedded in a thin, colourless to pale brown mucilaginous sheath that may appear partially dissolved or diffusely deliquescent. Vegetative cells are rectangular to slightly elongated (barrel-shaped), with somewhat constricted cross-walls that are occasionally indistinct. Cell width at the trichome base ranges from 5 to 8 μm. Apical cells are elongated and often form twisted, hair-like structures that curve outward from the colony centre. Heterocytes are spherical to slightly oval or cylindrical (9.5-14 μm in diameter), occurring singly or in pairs, and positioned either at the trichome base or intercalated among vegetative cells. Akinetes are large, smooth-walled, cylindrical with rounded ends, hyaline, and generally extracellular (exospores). They are arranged in linear series and may be separated by senescent vegetative cells or deteriorated heterocytes, measuring 55-154×7-14 μm. Within Gloeotrichia, this species is characterized by very large, loosely coherent colonies, a thin and fragile sheath, conspicuous hair-like apical cells, and relatively large, often extracellular akinetes. In contrast, congeners such as G. natans and G. aurantiaca typically exhibit more compact colony architecture and persistent, stratified sheaths (the latter with a diagnostic orange-brown inner layer), and differ in heterocyte/akinete placement and trichome length/tapering.

Occurrence and Ecology. Observed in a shallow, freshwater wetland dominated by emergent macrophytes, characterised by lentic flow, moderate water clarity and low nutrient input. Environmental conditions at the sampling time were: pH 6.9, temperature 20.4°C and dissolved oxygen 10.1 mg L^-1. The waterbody was unpolluted and located in a mid-temperate island climate. Although previously reported from temperate Europe and East Asia, this record from Jeju Island extends its known biogeographic range.

Sampling Site. Monmulgak Wetland, Jeju-si (St. 8; 33° 31ʹ06ʺN, 126°42ʹ55ʺE).

Voucher Specimen. DAEJIN-20201015.

Remarks.Gloeotrichia intermedia is morphologically distinguished by loosely coherent, fragile colonies, thin/deliquescent sheath, elongated, outward-twisting apical cells, and large, frequently extracellular akinetes. Differential diagnosis from G. natans and G. aurantiaca rests on the combination of sheath texture (thin vs. persistent/ stratified), colony compactness (loose vs. compact), and the arrangement/size of akinetes and heterocytes, together with the distinctive hair-like apical trichome tips. LM figures (Fig. 3A, B) indicate these diagnostic characters, and the Korean material conforms to them, supporting a provisional record of G. intermedia in Jeju Island wetlands. Given the known morphological similarity among Gloeotrichia species, molecular corroboration (e.g., 16S, rbcL, ITS) is desirable to refine species-level placement and phylogenetic relationships.

11. Gloeotrichia kamtschatica (Elenkin) Poljansij in Elenkin, 1938 (Fig. 3C, D)

Synonyms.Rivularia kamtschatica Elenkin 1907; Gloeotrichia natans var. kamtschatica Elenkin 1915 (Sources: Komárek 2013; AlgaeBase 2023).

References. Komárek, J. (2013). Cyanoprokaryota 3. Teil: Heterocytous Genera. Süsswasserflora von Mitteleuropa, Vol. 19/3. Springer Spektrum, Heidelberg. p. 369, fig. 433. Elenkin, A.A. (1938). Monographia algarum cyanophycearum aquidulcium et terrestrium in finibus URSS inventarum, Pars 2. Moscow-Leningrad: Academia URSS. AlgaeBase - Gloeotrichia kamtschatica (Accessed 2023).

Description. Colonies are spherical, compact, and composed of densely packed trichomes radiating outward from a central point (see Fig. 3C, D). They are light green and reach approximately 3 mm in diameter. Trichomes are embedded in a thin, colourless gelatinous sheath and are relatively short, with basal widths of 7-12 μm. Trichomes taper slightly toward the apex but lack apical hairs, and do not protrude beyond the mucilage. Terminal cells are bluntly conical, and the overall colony appears more truncated and compact than in related taxa. Vegetative cells are cylindrical to oval (5-11 μm long, 4-7 μm wide) with conspicuously constricted cross-walls. Heterocytes are spherical to oval, located singly near the base of the trichome, and measure up to ~11 μm in diameter. Akinetes are elongated, cylindrical, and slightly thickened at both ends. They may appear straight or slightly curved, measuring 50-300 μm in length and 7-12 μm in width. Within Gloeotrichia, the diagnostic combination for this taxon comprises short trichomes that remain within a thin, colorless sheath, absence of apical hairs, bluntly conical terminal cells, and exceptionally large, cylindrical akinetes (often 50- 300 μm). In contrast, congeners such as G. natans and G. intermedia generally show longer trichomes with hair-like apices and more diffuse or fragile sheaths, while G. aurantiaca possesses a persistent, stratified sheath with an orange-brown inner layer not observed here.

Occurrence and Ecology. Collected from a macrophyte- dominated, unpolluted freshwater wetland with oligotrophic characteristics. The sampling location exhibited stable hydrology and likely supports coldadapted or relict taxa due to its volcanic origin and moderate climatic regime.

Sampling Site. Monmulgak Wetland, Jeju-si (St. 8; 33° 31ʹ06ʺN, 126°42ʹ55ʺE).

Voucher Specimen. DAEJIN-20201015.

Remarks.Gloeotrichia kamtschatica is morphologically and ecologically distinctive, characterized by absence of apical hairs, short, non-emergent trichomes, blunt conical apices, and very large akinetes. These features separate it from G. natans and G. intermedia (Komárek and Anagnostidis 1986, 1998; Hindák 2008; Komárek 2013;Gabyshev et al. 2023). The lack of elongated apical hairs is consistent with benthic-epiphytic habit and reduced buoyancy demand (Maberly 2014), and the large akinetes align with persistent resting strategies under seasonal or thermal stress (Cottingham et al. 2021). LM figures (Fig. 3C, D) indicate the diagnostic set-short, hairless trichomes within a thin sheath; bluntly conical terminal cells; and very large cylindrical akinetessupporting a provisional record of G. kamtschatica in Korean inland waters.

12. Gloeotrichia pisum Thuret ex Bornet & Flahault, 1886 (Fig. 3E, F)

Synonyms. None reported.

References. Komárek, J. (2013). Cyanoprokaryota 3.

Teil: Heterocytous Genera. Süsswasserflora von Mitteleuropa, Vol. 19/3. Springer Spektrum, Heidelberg. p. 369, fig. 433; Bornet, É. & Flahault, C. (1886). Révision des Nostocacées hétérocystées contenues dans les principaux herbiers de France. Annales des Sciences Naturelles, Botanique, Sér. 7, 3: 323-381; Whitford, L.A. & Schumacher, G.J. (1973); Hindák, F. (2008).

Description. Colonies are compact, spherical and light green, ≈2-3 mm in diameter (see Fig. 3E, F). Trichomes are densely and radially arranged from a common center; their bases are embedded in a thin, colorless, firm, non-stratified mucilage. Trichomes are short and gradually tapering, composed of several cylindrical to oval vegetative cells (5-11 μm long), and lack apical hairs; terminal cells are bluntly conical. Basal cell width is 7-12 μm, tapering to 4-7 μm near the apex. Heterocytes are single, basal, spherical to ellipsoidal (~11 μm). Akinetes are long, cylindrical with rounded ends, slightly curved or straight, with thickened walls, ≈50-300× 7-12 μm, arranged in short linear series. The gelatinous matrix remains close to the colony boundary (no extended sheath), indicating a benthic-epiphytic habit. LM figures annotate (i) the absence of apical hairs, (ii) basal heterocyte position, and (iii) cylindrical akinetes with arrows for rapid diagnosis.

Occurrence and Ecology. Slightly acidic-neutral volcanic freshwater wetland surrounded by dense macrophytes; low nutrient loads and minimal disturbance.

Sampling Site. Monmulgak Wetland, Jeju-si (St. 8; 33° 31ʹ06ʺN, 126°42ʹ55ʺE).

Voucher Specimen. DAEJIN-20201015.

Remarks. Within Gloeotrichia, G. pisum is diagnosed by the combination of (i) compact spherical colony, (ii) thin, firm, non-stratified sheath, (iii) short, non-emergent trichomes without apical hairs, and (iv) conspicuous cylindrical akinetes arranged in series. This set separates G. pisum from G. natans (longer trichomes with hair-like tips and more extended mucilage), G. intermedia (looser colonies with fragile sheath and more frequently extracellular akinetes), and G. aurantiaca (persistent stratified sheath with an orange-brown inner layer); it is further distinguished from G. kamtschatica by more compact colony architecture and gradual trichome tapering within a thin, non-stratified sheath. Korean material conforms to these characters, supporting a provisional record of G. pisum in inland waters of Korea; molecular corroboration (e.g., 16S, rbcL, ITS) is recommended due to known interspecific similarity in the genus.

Genus Hydrocoryne Hansgirg, 1888

13. Hydrocoryne spongiosa Schwabe ex Bornet & Flahault, 1886 (Fig. 3G-J)

Synonyms. None reported.

References. Anagnostidis (2008), p. 840, fig. 1069; Bornet, É. & Flahault, C. (1886). Hydrocoryne spongiosa, in Journal de Botanique, 1: 276.

Description. Colonies appear as flat, plate-like structures with irregular green coloration, ranging from microscopic to macroscopic size (see Fig. 3G-J). Trichomes are loosely twisted and 4-7 μm wide. Typically, 5-6 trichomes radiate from a common center to form a plate ≈35 μm in diameter, and occasional false branching may occur. Each trichome is enclosed in a thin, colorless mucilaginous sheath and composed of barrelshaped to subspherical vegetative cells with slightly constricted cross-walls. Terminal cells are not tapered. Cells are light blue-green and 3-5 μm in diameter. Heterocytes are solitary, basal, oval to ellipsoid, 4-8× 4-5 μm. Akinetes were not observed. Within Hydrocoryne, the diagnostic combination includes a radial, plate-like colony of multiple loosely twisted trichomes, basal heterocytes, and absence of long emergent apical hairs. Superficially similar heterocytous genera are separable by colony architecture and branching: Stigonema typically exhibits true branching and tuft-like mats rather than discrete plates; Scytonema shows characteristic false branching with layered sheaths and more filamentous cushions; Symplocastrum forms dense fascicles and lacks the discrete radial plates evident in Hydrocoryne.

Occurrence and Ecology. Found attached to submerged macrophytes and detritus in a nutrient-rich floodplain wetland with slow-flowing water.

Sampling Site. Gyeongan-cheon Wetland Ecological Park, Gwangju-si, Gyeonggi-do (St. 3; 37°27ʹ32ʺN, 127° 18ʹ15ʺE).

Voucher Specimen. DAEJIN-20210716.

Remarks.Hydrocoryne spongiosa is a distinctive member of Stigonemataceae characterized by radially plated colony formation and multiple loosely twisted trichomes embedded in a common mucilage. Historical descriptions originate from European freshwaters (Bornet and Flahault 1886), with subsequent records from lowland wetlands and floodplain environments in the literature. LM figures (Fig. 3G-J) indicate the diagnostic set-radial plate organization with 5-6 trichomes, basal heterocytes, and absence of emergent apical hairs-supporting a provisional record of H. spongiosa in Korean floodplain wetlands. Given the scarcity of recent molecular data for Hydrocoryne, targeted sequencing (e.g., 16S rRNA, rbcL) would be valuable for confirming phylogenetic placement and assessing potential cryptic diversity.

Genus Wollea Bornet, É. & Flahault, C. 1888

14. Wollea saccata (Wolle) Bornet & Flahault, 1888 (Fig. 3K-M)

Synonyms. None reported.

References.Komárek (2013), p. 619, fig. 739; Bornet and Flahault (1888), in Journal de Botanique, 2: 45.

Description. Colonies are digitiform to cylindrical, composed of loosely aligned trichomes embedded in a homogeneous, transparent mucilage (see Fig. 3K-M). The mucilage shows an uneven, gelatinous surface. Trichomes are cylindrical with slightly constricted crosswalls and non-tapering apices. Vegetative cells are cylindrical to elongate barrel-shaped, 5-6 μm long and 4-5 μm wide. Terminal cells are blunt and resemble adjacent vegetative cells. Heterocytes are spherical to oval, 6-7×5-6 μm, larger than neighboring vegetative cells. Akinetes are elongate-oval, 15-20×7-10 μm, with smooth thickened walls, and are typically adjacent to heterocytes. Within Wollea, the diagnostic set comprises digitiform/cylindrical colony habit, blunt non-tapering trichome ends, and heterocytes with adjacent akinetes in a homogeneous, transparent mucilage. LM figures annotate (i) digitiform colony shape, (ii) non-tapering trichome apices with slight cross-wall constriction, and (iii) heterocyte-adjacent akinetes with arrows.

Occurrence and Ecology. Gelatinous colonies in shallow, vegetated freshwater margins of a floodplain wetland; slow-moving to stagnant waters with high organic matter and dense macrophytes.

Sampling Site. Hanyang Dongji Pond, Sejong-si, Republic of Korea (St. 6; 36°27ʹ46ʺN, 127°15ʹ44ʺE).

Voucher Specimen. DAEJIN-20230808.

Remarks.Wollea saccata can resemble Nostoc and Cylindrospermum, but is separated by the finger-like (digitiform) colony architecture, transparent homogeneous mucilage, and non-tapering trichome apices; Nostoc typically forms spherical to lobed gelatinous masses with more compact filament arrays, while Cylindrospermum shows conspicuous terminal heterocytes with adjacent akinetes at filament ends and generally narrower rod-like trichomes. Korean material exhibits the diagnostic combination shown in Figure 3K-M, supporting a provisional record of W. saccata in inland waters of Korea; molecular corroboration (e.g., 16S rRNA, rbcL) would refine phylogenetic placement and evaluate potential cryptic diversity.

Family Nostocaceae

Genus Nostoc Agardh ex Bornet et Flahault, 1888

15. Nostoc carneum Agardh ex Bornet et Flahault, 1888 (Fig. 3N, O)

Synonyms. None reported.

References.Komárek (2013), p. 968, Fig. 1261; Bornet and Flahault (1888), Journal de Botanique, 2: 62.

Description. Colonies are substrate-attached, compact clusters (see Fig. 3N, O). Trichomes are very short (≈≤60 μm long, ≈12 μm wide), gradually tapering toward the ends, and embedded in a thick, funnelshaped, multilayered (stratified) colorless mucilage. Vegetative cells are mostly rectangular near the trichome base, becoming barrel-shaped to short-cylindrical toward the middle; cell length is generally less than width. A single basal heterocyte is present and ovoid, slightly narrower than adjacent vegetative cells. Akinetes were not observed in the examined material. Within Nostoc, the diagnostic combination of (i) compact, sessile colonies, (ii) very short trichomes in a thick, stratified funnel-shaped sheath, and (iii) a solitary basal heterocyte separates this taxon from congeners such as N. commune (typically larger gelatinous thalli with longer trichomes and more diffuse gelatin) and N. linckia (bundle-forming filaments with more elongated trichomes and different colony architecture). LM figures annotate (i) the stratified funnel-shaped sheath, (ii) the basal heterocyte position, and (iii) trichome shortness with arrows.

Occurrence and Ecology. Collected from a marginal wetland zone; attached to submerged substrates in slow/ stagnant, slightly eutrophic water.

Sampling Site. Hanyang Dongji Pond, Sejong-si, Republic of Korea (St. 6; 36°27ʹ46ʺN, 127°15ʹ44ʺE).

Voucher Specimen. DAEJIN-20230808.

Remarks.Nostoc carneum is characterized by very short trichomes embedded in a thick, stratified, funnelshaped mucilage and a solitary basal heterocyte; these features distinguish it from morphologically similar Nostoc taxa noted above. Korean material conforms to this character set, supporting a provisional record of N. carneum in inland waters of Korea; absence of akinetes is interpreted as a life-cycle/state effect.

Family Rivulariaceae

Genus Calothrix Agardh ex Bornet and Flahault, 1886

16. Calothrix brevissima G.S. West, 1907 (Fig. 3P, Q)

Synonyms. None reported.

References.Komárek (2013), p. 244, Fig. 251; West, G.S. (1907). Freshwater Algae of the English Lake District. p. 77.

Description. This species forms firmly substrateattached (sessile) colonies in compact groupings (see Fig. 3P, Q). Trichomes are very short (generally ≈60 μm long, <7 μm wide), slightly tapering apically and without terminal hairs; each is surrounded by a narrow, firm, colorless, non-lamellated sheath that is cylindrical and unbranched. Vegetative cells are quadrate near the base, becoming barrel-shaped to cylindrical toward the apex; cell width <5 μm and cell length <width. A single basal heterocyte occurs in each trichome (spherical to oval, ~5 μm); paired heterocytes were not observed. Within Calothrix, the diagnostic combination of (i) very short, slightly tapering trichomes lacking apical hairs, (ii) a narrow, firm, non-lamellated sheath, and (iii) a single basal heterocyte separates this taxon from congeners (e.g., C. parietina, C. confervicola, C. marchica), which typically show longer trichomes and/or conspicuous apical hairs with more expanded sheaths. Superficially similar rivularioid genera (e.g., Macrochaete) differ by prominent setae-like apical hairs and generally larger trichome dimensions. LM figures annotate (i) apical hair absence, (ii) narrow firm sheath, and (iii) basal heterocyte position with arrows for rapid diagnosis.

Occurrence and Ecology. Periphytic on submerged substrates in a shallow freshwater marsh; slow-flowing, nutrient-rich water with abundant macrophyte cover.

Sampling Site. Hanyang Dongji Pond, Sejong-si, Republic of Korea (St. 6; 36°27ʹ46ʺN, 127°15ʹ44ʺE).

Voucher Specimen. DAEJIN-20230805.

Remarks.Calothrix brevissima is a diminutive rivularioid cyanobacterium with heteropolar trichomes (false branching absent in the examined material) and basal heterocytes. The Jeju/Sejong material matches the Calothrix morphological concept summarized above, but given evidence for polyphyly within “Calothrix” and recent segregate proposals (e.g., lineages allied to Dulcicalothrix), molecular corroboration (16S, ITS, rbcL) is required to test generic placement; accordingly, the present account is treated as a provisional record based on morphology. LM figures (Fig. 3P, Q) present the diagnostic set-very short trichomes without apical hairs, a narrow firm sheath, and a single basal heterocyte- supporting the identification under the current morphological circumscription of C. brevissima.

Family Stigonemataceae

Genus StigonemaBornet & Flahault, 1887

17. Stigonema minutum Hassall ex Bornet & Flahault, 1887 (Fig. 4A-C)

Synonyms. None reported.

References.Komárek (2013), p. 619, Fig. 739; Bornet, É. & Flahault, C. (1887). Revision des Nostocacées hétérocystées. Annales des Sciences Naturelles, Botanique, Série 7, 6: 323-381.

Description. Thalli form leathery, thin, crustose layers with dark brown to blackish coloration (see Fig. 4A-C). Trichomes creep over substrates and exhibit frequent true branching; upright branches are narrower than the parent axis. Each trichome is enclosed by a firm, laminated, pale-yellow to golden mucilaginous sheath. Trichomes are multiseriate (commonly 2-4-seriate) along the main axis, becoming biseriate to uniseriate near the tips; trichome width is 15-28 μm. Cells are deep bluegreen, spherical to oval, 7-13 μm in diameter. Heterocytes are frequent at branch bases or intercalary and are conspicuously differentiated. Within Stigonema, this taxon is characterized by the combination of crustose, leathery thalli, firm laminated sheath, frequent irregular true branching, and transition from multi- to uni/biseriate apices. Superficially similar heterocytous taxa can be separated by branching/sheath traits: Scytonema exhibits false branching and typically thicker, layered sheaths forming filamentous cushions (not crustose plates), whereas larger congeners of Stigonema (e.g., S. ocellatum sensu lato) tend to have broader, more robust axes and thicker sheaths.

Occurrence and Ecology. Observed at Monmulkkak Wetland, Jocheon-eup, Jeju-si, Republic of Korea. This species was found attached to submerged mosses and shaded rocks in a slightly acidic, oligotrophic freshwater wetland.

Sampling Site. Monmulgak Wetland, Jeju-si (St. 8; 33° 31ʹ06ʺN, 126°42ʹ55ʺE).

Voucher Specimen. DAEJIN-20230702.

Remarks.Stigonema minutum is a compact, crustforming species of a genus defined by multiseriate trichomes with true branching. Diagnostic separation from Scytonema rests on the presence of true (vs. false) branching and on the crustose habit with a firm laminated sheath; within Stigonema, S. minutum is smallerscaled, with shorter axes and a thinner sheath than larger congeners. Reports of moss-associated Stigonema in cool, low-nutrient habitats are consistent with the observed microhabitat on bryophyte mats. Recent work indicates that bryophytes provide structure and moisture retention favorable to cyanobacterial epiphytes under low-nutrient regimes, where heterocytes contribute substantially to nitrogen fixation. LM figures (Fig. 4AC) indicate the diagnostic set-leathery crusts, frequent true branching with narrower upright branches, firm laminated sheaths, and multiseriate axes grading to uni/biseriate apices-supporting a provisional record of S. minutum in Korean inland wetlands.

Family Scytonemataceae

Genus ScytonemaBornet & Flahault, 1886a

18. Scytonema ocellatum Lyngbye ex Bornet & Flahault, 1886b (Fig. 4D, E)

Synonyms. None reported.

References.Komárek (2013), p. 75, Fig. 37; Bornet and Flahault (1886b), Annales des Sciences Naturelles, Botanique, Série 7, 3: 323-381; AlgaeBase (2023).

Description. The thallus forms dense, amorphous mats with dark grey to blue-green or nearly black pigmentation (see Fig. 4D, E). Colonies reach up to ~3 mm in diameter and are typically epilithic. Trichomes are entangled and frequently exhibit false dichotomous branching. Individual trichomes are 10-19 μm wide and enclosed in a firm, yellowish-brown, non-lamellated sheath. Vegetative cells are rectangular to short-cylindrical, 4-10 μm wide. Heterocytes are terminal or intercalary and usually similar in width to adjacent vegetative cells. ^**Within Scytonema, this species is characterized by the conspicuous false branching, firm nonlamellated sheath with brownish pigmentation, and mat-forming habit; it is readily separated from superficially similar heterocytous genera by branching/sheath traits-Stigonema shows true (not false) branching with laminated sheaths, whereas Symplocastrum forms dense fascicles lacking the amorphous mat architecture typical of S. ocellatum.

Occurrence and Ecology. This species was found growing on moist, shaded rocks in the freshwater wetland of Monmulgak, Jocheon-eup, Jeju-si, Republic of Korea. It formed dark pigmented mats under low-light conditions in an oligotrophic aquatic environment.

Sampling Site. Monmulgak Wetland, Jeju-si (St. 8; 33° 31ʹ06ʺN, 126°42ʹ55ʺE).

Voucher Specimen. DAEJIN-20201015.

Remarks.Scytonema ocellatum is widely distributed in freshwater and terrestrial microhabitats and is noted for false branching and production of UV-screening pigments (e.g., scytonemin) associated with its dark coloration. Differential diagnosis from co-occurring heterocytous taxa in the study area rests primarily on branching mode (false vs. true) and sheath architecture/ pigmentation. LM figures (Fig. 4D, E) show the diagnostic combination-false dichotomous branching, firm brownish sheath, and mat-forming thalli-supporting a provisional record of S. ocellatum in Korean inland wetlands.

4. DISCUSSION

This study significantly expands the known diversity of cyanobacteria in Korea, documenting 18 taxa previously unrecorded in national floristic inventories. These taxa represent a broad spectrum of morphological forms-unicellular, colonial, filamentous, and heterocytous- and were collected from diverse aquatic environments, including eutrophic lakes, oligotrophic mountain streams and brackish estuaries.

Globally, cyanobacteria are a phylogenetically diverse and ecologically vital group, inhabiting virtually all aquatic and terrestrial habitats from Antarctic lakes to tropical coral reefs, often dominating primary production in nutrient-rich waters (Komárek et al. 2014;Dvořák et al. 2017). The genus-level diversity, especially among Nostocales and Oscillatoriales, is essential for understanding nitrogen fixation, bloom dynamics and biofilm development (Komárek 2006;Castenholz 2015). Several genera recorded in this study-such as Gloeotrichia, Woronichinia and Dolichospermum-are wellknown contributors to harmful algal blooms (Huisman et al. 2018), whereas others like Gomontiella and Hydrocoryne are rarely documented and point to underexplored microhabitats.

Historically, Korean cyanobacterial studies have emphasized bloom-forming taxa such as Anabaena, Microcystis, Aphanizomenon and Oscillatoria (Li et al. 2013;Byun et al. 2014;Ryu et al. 2018;Lee et al. 2020;Woo et al. 2020). Earlier floristic surveys, primarily based on light microscopy, likely underrepresented cryptic or morphologically subtle taxa due to limitations in taxonomic resolution and uneven seasonal or habitat-based sampling (Park 2012a, 2012b). Recent national efforts by institutions such as NNIBR and NIBR have improved the documentation of rare and endemic taxa, especially in mountain wetlands, island ponds and estuarine zones (Park et al. 2011;NIBR 2017, 2024;NNIBR 2017, 2018;Chung et al. 2019;Park et al. 2024).

Species such as Calothrix brevissima, Stigonema minutum and Trichormus ellipsosporus exhibit basal heterocytes and complex trichome structures-traits often associated with nitrogen fixation and colonization in nutrient-poor or disturbed environments (Berrendero et al. 2008;Thajuddin et al. 2010;Singh et al. 2011;Muñoz-Martín et al. 2020;Álvarez et al. 2023). Others, like Wollea saccata and Hydrocoryne spongiosa, exhibit ecological plasticity and may signal transitional habitats or saline influence in estuarine systems. The discovery of Gomontiella subtubulosa, a species typically reported from Mediterranean and subtropical zones (Bohunická et al. 2015), suggests that Korea’s microclimatic and hydrological variability supports broader cyanobacterial diversity than previously recognized.

In comparison with global inventories (Komárek et al. 2014; AlgaeBase 2023; Strunecký et al. 2023), Korea’s cyanobacterial flora remains incomplete, particularly in under-surveyed habitats such as splash zones, rice paddies, rocky headwaters and insular wetlands. In these marginal environments, genera like Schizothrix, Lyngbya and Phormidium often dominate subaerial mats or crusts, yet remain poorly documented in Korea outside anecdotal records (Kim and Kim 2008; Han et al. 2017). The present study contributes toward filling these gaps by offering voucher-supported identifications from such underrepresented sites.

Taxonomic challenges-especially in morphologically plastic or convergent genera such as Leptolyngbya, Phormidium and Woronichinia-underscore the critical need for polyphasic approaches in cyanobacterial systematics. To overcome limitations of morphologybased identification, future studies should incorporate molecular markers such as 16S rRNA, rbcL, and ITS regions to resolve phylogenetic relationships, particularly for taxonomically ambiguous or poorly described taxa like Gomontiella and Hydrocoryne (Hoffmann et al. 2005;Komárek 2013; Shih et al. 2013).

Overall, this study reinforces the notion that a significant portion of Korea’s cyanobacterial diversity remains undocumented-particularly in ecologically marginal, seasonally dynamic or geographically isolated habitats not typically covered by routine monitoring programs. Targeted floristic surveys, when combined with molecular diagnostics, are essential not only for accurate biodiversity assessments but also for informing long-term ecosystem monitoring, conservation policy and the discovery of novel microbial resources with biotechnological potential.

From an ecological and conservation perspective, the taxa documented in this study serve as important indicators of habitat specificity, water quality and ecosystem transitions. The presence of nitrogen-fixing genera such as Dolichospermum, Calothrix and Stigonema in nutrient-poor or isolated wetlands suggests ecological resilience mechanisms in otherwise oligotrophic systems. Conversely, the identification of bloom-forming species like Microcystis botrys and Gloeotrichia aurantiaca points to sites with eutrophic tendencies or seasonal nutrient influx. Notably, Jeju Island’s Monmulgak Wetland-hosting multiple novel taxa-emerges as a biodiversity hotspot warranting targeted protection. Given the accelerating pressures from urban development, agricultural runoff and climate-driven hydrological shifts in Korea, the recognition and preservation of such insular and transitional habitats are crucial. In corporating cyanobacterial diversity into routine ecological assessments and conservation strategies will be essential for detecting ecosystem change, maintaining microbial biodiversity and safeguarding the ecological services that these photosynthetic prokaryotes provide.

Importantly, our taxonomic treatment follows the modern classification of Komárek et al. (2014) and AlgaeBase (2023), and has been updated in light of the phylogenomics-based reclassification proposed by Strunecký et al. (2023). Under this framework, certain genera have been reassigned compared to older systems: for example, Cyanothece is placed in Gomontiellales (rather than Chroococcales), and Lemmermanniella is placed in Nodosilineales (rather than Synechococcales). We adopted this revised taxonomy to ensure consistency with contemporary polyphasic approaches. Although this differs from traditional classifications used in some earlier Korean literature (Park 2012a, 2012b), clarifying these updates is essential for maintaining alignment with international standards and for ensuring reproducibility in future biodiversity monitoring efforts.

At the same time, we acknowledge that molecular phylogenetic analyses were not conducted in this study because sufficient isolates for culture and sequencing were not obtained. This limitation is explicitly recognized as a weakness of the present work. However, in our ongoing projects involving novel species descriptions, we are already applying a fully integrated polyphasic approach that includes isolation, culture, morphological documentation and molecular sequencing. Although official accession numbers were not obtained in this study, voucher specimens were internally preserved. In future studies-even when the taxa are not newly described species-we will ensure culture isolation, molecular analyses, and the formal deposition of voucher specimens in official repositories (e.g., NNIBR, KCTC).

5. CONCLUSION

This study newly documents 18 previously unrecorded taxa of cyanobacteria (Cyanophyceae) from freshwater and brackish environments across South Korea. Specimens were collected from 43 ecologically diverse aquatic habitats-including lakes, ponds, wetlands, rivers and estuarine zones-during targeted surveys conducted in 2017 and 2024. These taxa encompass a wide spectrum of morphological types, including unicellular, colonial, filamentous, and heterocytous forms, and represent substantial additions to the national cyanobacterial inventory. The discovery of these taxa highlights the ecological richness and habitat specificity of Korean aquatic ecosystems, particularly in transitional and geographically isolated sites such as Jeju Island’s wetlands. These findings emphasize the critical need for continued floristic exploration using both classical and molecular approaches, especially in under-surveyed or dynamic habitats. Beyond their taxonomic relevance, the documented species serve as ecological indicators and potential microbial resources, contributing valuable baseline data for future studies in systematics, biogeography, water quality assessment, and sustainable bioresource development.