Unrecorded liverwort species from Korean flora V: New data on <i>Riccia</i> (Marchantiophyta) from Korean Islands

Hyun Min BUM; Seung Jin PARK; Seung Hoon LEE; Vadim A. BAKALIN; Myung-Ok MOON; Seung Se CHOI

doi:10.11110/kjpt.2025.55.4.290

Abstract

During a floristic survey of coastal and island regions of Korea, we identified two previously unrecorded species of the genus Riccia L. (Ricciaceae): Riccia cavernosa Hoffm. and R. nipponica S. Hatt. R. cavernosa, originally described from Germany and widely distributed across the Holarctic region, was newly confirmed in Korea from Gyodongdo Island (Incheon) and Gangneung (Gangwon-do). R. nipponica, previously known from Japan, China, and the Russian Far East, was newly discovered on Jeju-do, typically inhabiting moist soils in rice-field habitats. Detailed morphological descriptions, illustrations, and diagnostic characters distinguishing these taxa from morphologically similar Korean species, in this case R. huebeneriana and R. glauca, are provided. These results highlight the importance of continuous bryofloristic investigations, particularly in underexplored habitats such as islands and agricultural wetlands, for a more comprehensive understanding of the liverwort flora of Korea.

Keywords: islands, Riccia, L. cavernosa, L. nipponica, unrecorded taxa

INTRODUCTION

The genus Riccia L. typically inhabits shaded and moist soils along paddy fields, farmlands, reservoirs, and stream margins. As reflected in its Korean name “Dung-geun-i-kki” (meaning “round liverwort”), members of the genus characteristically grow in rosette-like, rounded forms. The genus Riccia is one of the most widely distributed thalloid liverworts, occurring across diverse climatic regions worldwide (Schuster, 1992; Borovichev and Bakalin, 2016).

The genus Riccia comprises approximately 255 species worldwide, with 20 species reported from China, 17 from Japan, and 13 from the Russian Far East (Piippo, 1990; Borovichev and Bakalin, 2016; Söderström et al., 2016; Katagiri and Furuki, 2018). In Korea, six species have been reported, excluding Riccia pseudofluitans C. Gao et G. C. Zhang, which is distributed in Jilin Province, China (Choi et al., 2021). However, the distribution, ecology, and taxonomy of the remaining Korean species are still poorly understood, underscoring the need for further floristic and systematic investigations.

The first records of the genus Riccia in Korea were reported by Horikawa (1934, 1939) with R. fluitans L. and R. glauca L. Subsequent major bryological references for the Korean Peninsula include Hong (1962), who listed two species (R. fluitans and R. glauca), and Choe (1980), who recorded six taxa: R. fluitans, R. glauca, R. glauca var. subinermis (L.) Warnst. (= R. glauca), R. huebeneriana Lindenb., R. pseudofluitans (from the Amrok River), and R. sorocarpa Bisch. In North Korea, Kim and Hwang (1991) reported three species, R. fluitans, R. glauca, and R. huebeneriana. More recently, Choi (2020b) reported two additional unrecorded species for the Korean flora, R. beyrichiana Hampe and R. bifurca Hoffm., from Jeju Island.

The present account continues the series of articles especially devoted to the description of new records in the Korean liverwort flora (Choi et al., 2012a, 2012b, 2020a, 2020b). In this study, we report R. cavernosa and R. nipponica as unrecorded species of Korean flora identified on Jejudo and Gyodongdo Islands during the coastal and Islands surveys.

Taxonomic Treatment

Riccia cavernosa Hoffm., Deutschl. Fl. 2: 95, 1795 (1796) (Fig. 1. A–E).—TYPE: GERMANY. ‘In terra limosa, ad piscinus,’ Hoffmann, Herb. Weber. (not seen).

Korean name: 천둥근이끼(Cheon-dung-gun-i-kki).

Plants rosettes or discrete, 3.0–6.5 mm in diameter, light green to yellowish green, rarely with purplish pigmentation. Thalli 4.0–7.0 mm long, 1.5–2.5 mm wide, repeatedly dichotomously furcate; ultimate branches shortly to deeply divided, and overlapping; obcuneate or obovate to oblong; upper surface slightly to strongly distinctly lacunose or alveolate, air chambers gradually coalesce generally in older parts of thallus; apex rounded, shortly emarginate; median furrow distinct at apex; rounded in cross-section, obtuse. Dorsal epidermis cells polygonal, shiny, 60.0–75.0 × 45.0–55.0 μm, thin to thick-walled; cross-section plane-convex to slightly biconvex; 1.5–3.0 times wider than thick; assimilation tissue high, spongy; up to 600.0–800.0 μm thick; air chambers large, polygonal; in 2–4 layers in the middle; ventral tissue parenchymatous, consisting of thin-walled cells. Ventral surface flat or weakly convex, green; thallus branches midrib fleshy, 650.0–950.0 μm thick in cross-section. Rhizoids smooth and pegged, hyaline, covering ventral surface of midrib of thallus. Ventral scales absent or vestigial. Monoicous. Antheridia in a row along midline of the thallus, visible through the hole of the lacunose thallus surface. Archegonia in deeply embedded rows, with purple or brownish necks, not prominent. Sporangia numerous, slightly bulging ventrally. Spores 65–95 μm in diameter; reddish to dark brown; distal face convex, with irregular short and low toward margin lamellae; lamellae minutely papillose; proximal face covered by simple or branched lamellae.

Habitat: On moist, semi-shaded slightly sandy mud soil around drained reservoirs, with Phragmites australis (Cav.) Trin. ex Steud., Setaria viridis (L.) P. Beauv., and Fimbristylis squarrosa Vahl.

Distribution: Eurasia, North America, Europe, Africa, Holarctic, subcosmopolitan, temperate circumpolar, Korea (Incheon-si, Gangwon-do).

Specimens examined: KOREA. Incheon: Ganghwa-gun, Gyodong-myeon, Gyodongdo Island, 21 Jun 2024, H.M. Bum et a l. 2 4138 (JNU), HNIBRMS1761 (HIBR). Gangwon-do: Gangneung-si, Jukheon-dong, 2 Oct 2023, H.M. Bum et al. 231002 (2 sheets, JNU).

Riccia cavernosa was first described from Germany, characterized by the presence of numerous small lacunose on the thallus surface (Hoffmann, 1796), and has since been recognized as a cosmopolitan species (Rebergen et al., 2018). In Korea, R. cavernosa is morphologically similar to R. huebeneriana, which also exhibits a lacunose thallus surface. However, R. huebeneriana can be distinguished by its thallus margins gradually turning purplish, a relatively low density of surface perforations, and narrower thalli (0.3–1.2 mm vs. 1.5–2.5 mm in R. cavernosa). A new Korean name, “Cheondung-geun-i-kki,” is proposed, referring to its typical occurrence around reservoir habitats.

Riccia nipponica S. Hatt., J. Hattori Bot. Lab. 9: 38. f. 5, 1953 (Fig. 1. F–J).—TYPE: JAPAN. Miyazaki, 5 Feb 1953, S. Hattori and Shimizu 51535 (NICH, observed only figures!).

Korean name: 논둥근이끼(Non-dung-gun-i-kki).

Plants rosettes or semirosettes, not forming pure mats. Thalli 5.0–6.5 mm long, 2.5–5.0 mm wide; 2–4 times furcate; ultimate branches short, wide, obcordate; upper surface light green to bluish green; apex thick, rounded to shortly emarginate; median furrow distinct at apex; thallus margins raised, obtuse. Dorsal epidermis cells globular, shiny, 45.0–55.0 μm wide, thin-walled; cross-section elliptic, not furrowed; 3–5 times wider than thick; 400.0–600.0 μm thick, occupying 2/3–3/4 the thallus thickness in the middle; air chambers in 1–2 layers in the middle. Ventral tissue parenchymatous, thin-walled cells; occupies 1/4–1/3 of the thallus thickness in the middle. Ventral surface green; 600.0–800.0 μm thick in cross-section; relatively well defined. Rhizoids smooth and pegged, hyaline, covering ventral surface of the midrib of the thallus. Ventral scales near apex, hyaline, minute. Monoicous. Antheridia in two lateral rows along the thallus midline, necks hyaline, up to 150.0–180.0 μm long. Archegonia along thallus middle, with necks purple-brown colored, up to 180.0–210.0 μm long. Sporangia numerous, dorsal, slightly protruding ventrally. Spores 55.0–78.0 μm in diameter, light to dark yellowish or brownish, distal surface alveolate, with spine in the center of alveola; proximal surface distinct trilete scar.

Habitat: On moist, semi-shaded mud soil around or on rice fields during the autumn and winter seasons, under Cerastium glomeratum Thuill., Cardamine fallax (O. E. Schulz) Nakai, Lindernia procumbens (Krock.) Borbás, Anthoceros punctatus L., and Alopecurus aequalis Sobol.

Distribution: Japan (Honshu, Shikoku, and Kyushu), China (Guizhou), Russian Far East (Khabarovsk Territory), Korea (Jeju-do).

Specimens examined: KOREA. Jeju-do: Seogwipo-si, Hogeun-dong, 4 Feb 2022, H.M. Bum et al. 22025 (2 sheets, JNU), 28 Mar 2023, Bum et al. 23025 (JNU), HNIBRMS93 (HIBR).

Riccia nipponica was originally described as a new species by Shimizu & Hattori (1953) based on type specimens collected from Minaminaka-gun, Miyazaki Prefecture in Japan by Shimizu & Hattori in 1953. The species is characterized by thalli that are slightly lacunose towards the apex and sparsely lacunose in older portions, lobes 2.5–5.0 mm wide, and an upper surface bluish in younger parts, becoming grayish green or yellowish in older parts. R. nipponica is very similar to L. cavernosa in having lacunose thalli near the apex, but can be distinguished by its wider lobes (2.0–5.0 mm vs. 1.5–2.5 mm in R. cavernosa). A new Korean name, “Nondung-geun-i-kki,” is proposed, referring to its typical occurrence in rice-field habitats.

The following key to the related Korean Riccia taxa has been prepared for all species on the Korean Peninsula.

Key to the species of Riccia occurring in Korea

1. Dorsal thallus surface distinctly lacunose in older parts; spores exit through ventral or dorsal side of thallus.
- 2. Thalli yellow-green, with upper surface often having vinaceous red or purplish secondary pigmentation; thallus width 0.3–1.2 mm; terrestrial or aquatic.
  - 3. Thallus apex not or rarely slightly furrowed; thallus upper surface not lacunose; plants commonly sterile; aquatic ······················································································································ R. fluitans 물긴가지이끼
  - 3. Thalli distinctly furrowed towards apex; at least in older parts becoming distinctly lacunose to alveolate; numerous sporangia commonly present; terrestrial ······················································· R. hueberiana 아기밭둥근이끼
- 2. Thalli light green to yellowish green, upper surface very rarely with slightly purplish secondary pigmentation; thallus width 1.5–3(–5) mm; terrestrial.
  - 4. Thallus upper surface slightly to strongly and distinctly lacunose throughout; air chambers 2–3-layered in the middle; spores incompletely alveolate, lamellae without tubercles and spines at the angles ·········· R. cavernosa 천둥근이끼
  - 4. Thallus upper surface persistent or indistinctly lacunose towards the apex and often less conspicuously lacunose in older parts; air-chambers 1–2-layered in the middle; thallus spores strongly and completely alveolate ·· R. nipponica 논둥근이끼
1. Dorsal thallus surface not lacunose and alveolate; spores exit through dorsal side of thallus.
- 5. Distal face of spores with alveolar lamellae thick, with a few tubercles at the corners of the alveoli.
  - 6. Thalli 2.0–3.0 mm wide; cilia numerous near margins; spores larger 90.0–105.0 mm in diameter ······································································································································ R. beyrichiana 털밭둥근이끼
  - 6. Thalli 0.8–1.5 mm wide; cilia absent; spores smaller 65.0–85.0 mm in diameter ············· R. bifurca 돌밭둥근이끼
- 5. Distal face of spores with alveolar lamellae thin, with a lot of spinose tubercles at the corners of the alveoli.
  - 7. Thallus in cross-section 3–5 times wider than thick; median furrow distinct at apex, but immediately below apex becomes shallow and vanishing; distal face of spores slightly spinose-tuberculate ··························· R. glauca 밭둥근이끼
  - 7. Thallus in cross-section 2–3 times wider than thick; median furrow distinct at apex and continuing along most of the thallus length; distal face of spores distinctly spinose-tuberculate ····························· R. sorocarpa 초록둥근이끼

Unrecorded liverwort species from Korean flora V: New data on Riccia (Marchantiophyta) from Korean Islands

Abstract

INTRODUCTION

Taxonomic Treatment

Key to the species of Riccia occurring in Korea

NOTES

Fig. 1

LITERATURE CITED