A new generic record of <i>Chikusichloa</i> (Poaceae) for the flora of Korea

Seung Se CHOI; Keun-Hee HYUN; Seung Hoon LEE; Seong Gwon LEE; Jung-Hoon LEE; Jonghwan KIM; Myung-Ok MOON

doi:10.11110/kjpt.2025.55.4.295

Abstract

During a floristic investigation of Jejudo Island, we identified an unrecorded genus and species in Korea: Chikusichloa aquatica (Poaceae), previously known to be native to Japan and southern China. Based on data from the sixth National Ecosystem Survey, this species was recently found growing in a small muddy pond near Minoreum on Jejudo Island. In this study, we provide a detailed morphological description of the species, accompanied by photographs, and compare it with related taxa within the tribe Oryzeae found in Korea. A diagnostic key is also provided to facilitate the identification of related genera.

Keywords: Chikusichloa, C. aquatica, Jejudo Island, Poaceae, unrecorded genus

INTRODUCTION

During a floristic survey of Minoreum, a volcanic cone on Jejudo Island, as part of the sixth National Ecosystem Survey, we discovered a plant similar to Molinia japonica Hack. in a small muddy pond. The collected plant was brought to a laboratory, where a specimen was prepared and subjected to detailed morphological examination. As a result, it was confirmed that the plant does not belong to the genus Molinia but to Chikusichloa — a genus previously unrecorded in the flora of Korea.

The genus Chikusichloa belongs to the family Poaceae Barnhart, the subfamily Oryzoideae Kunth ex Beilschm, the tribe Oryzeae Martinov, and three species (C. aquatica Koidzumi, C. brachyathera Ohwi, C. mutica Keng) are distributed in eastern Asia and southeastern Asia. The family Poaceae is a very large family, comprising 789 genera and 11,783 taxa, and is distributed worldwide (Soreng et al., 2022). The tribe Oryzeae comprises 12 genera distributed throughout tropical and temperate regions (Clayton and Renvoize, 1986). In Korea, the family Poaceae comprises 94–109 genera and 212–348 species, and the tribe Oryzeae comprises three genera (Oryza L., Leersia S w ., Zizania L.) and five species (Korea National Arboretum, 2011; Cho et al., 2016; Lee, 2018; Kim et al., 2019).

The genus Chikusichloa was originally described in the tribe Paniceae by Koidzumi (1925), based on C. aquatica Koidz. from Kyushu. However, it was noted to be similar to Zizania L., which was considered to belong to the tribe Oryzeae (Keng, 1931), a finding supported by molecular phylogenetic studies (Ge et al., 2002; Soreng et al., 2022). The genus Chikusichloa consists mostly of perennial herbs in the tribe Oryzeae, characterized by bisexual spikelets, stipitate florets, linear leaf blades, and a single stamen (Ohwi, 1984; Liu and Phillips, 2006).

In this study, we report C. aquatica as an unrecorded species in the Korean flora, identified on Jejudo Island during the Sixth National Ecosystem Survey.

Taxonomic Treatment

Chikusichloa Koidzumi, Bot. Mag. (Tokyo) 39: 23, 1925.—TYPE: Chikusichloa aquatica Koidzumi.

Korean name: 이슬새속(I-seul-sae-sok).

Perennial. Culms tufted, erect, unbranched. Leaf sheaths longer than internodes; leaf blades linear or broadly linear, with transverse veinlets; ligules membranous. Inflorescence panicle, lax. Spikelets with 1 floret, weakly dorsally flattened at anthesis, becoming terete at maturity, floret borne upon a long slender stipe derived from floret callus, disarticulating at base of stipe; glumes usually absent, sometimes 2 vestiges at stipe base; lemma membranous, strongly 5–7-veined, apex acute or awned; palea slightly shorter than lemma, (2–)3(–5)- veined. Stamen 1. Fruits caryopsis, fusiform.

Species: 3 (C. aquatica, C. brachyathera Ohwi, C. mutica Keng)

Distribution: China, Taiwan, Japan, and Indonesia (Sumatra) (Liu and Phillips, 2006; Jung and Kuoh, 2007).

Chikusichloa aquatica Koidz., Bot. Mag. (Tokyo) 39: 23, 1925 (Figs. 1, 2).—TYPE: JAPAN. Kyushu, Kumamoto Pref., Taragi-mura by K. Mayebara in 5 Oct 1924 (lectotype: TNS, not seen).

Korean name: 한산이슬새(Han-san-i-seul-sae).

Plants perennial. Culms 60.0–140.0 cm tall, 3.0–8.0 mm thick. Leaf sheaths smooth, glabrous, keeled; leaf blades linear, flat, 30.0–50.0 × 0.6–1.3 cm, scabrous on both surfaces, narrowed toward base, apex long acuminate; ligule 1.5–2.5 mm. Panicle large, loose, 30–50 cm; branches usually solitary, ascending to spreading, smooth. Spikelets 10–17 mm (including stipe and awn), tinged purplish; disarticulation above pedicel with spinulose stipe; stipe 4–6 mm long; glume absent; lemma body lanceolate to narrowly ovate, ca. 4 mm long, 5-veined, spinulose along veins, apex acuminate, awned; awn 4–6 mm, scabrous; palea narrowly lanceolate, 3-veined, spinulose along veins. Anther 1.2–1.5 mm. Caryopsis fusiform, 2.1–2.5× 0.8–1.2 mm.

Flowering: Late August to early October, fruiting: September to early November.

Habitat: This species grows along a small muddy pond, in association with Boehmeria japonica (L. f.) Miq., Persicaria thunbergii (Siebold & Zucc.) H. Gross, Dryopteris crassirhizoma Nakai, Muhlenbergia hakonensis (Hack.) Makino, and Lophatherum sinense Rendle, within forests dominated by Acer pictum var. mono (Maxim.) Franch., Styrax japonicus Siebold & Zucc., and Prunus spachiana f. ascendens (Makino) Kitam.

Distribution: China (Jiangsu), Japan (Honshu, Kyushu), Korea (Jeju-do).

Specimens examined: KOREA. Jeju-do: Jeju-si, Minoreum, small pond, 15 Sep 2025, M.O. Moon, J.H. Kim & S.S. Choi 25009001 (6 sheets, JNU).

Chikusichloa aquatica was described as a new species by Koidzumi (1925) based on type specimens collected from Kyushu, Kumamoto Pref., Taragi-mura by K. Mayebara on 5 Oct 1924. C. aquatica is the only species within Chikusichloa in Korea that has awned spikelets, 4–6 mm basal stipe, reduced glumes, panicle, and leaf blades 0.6–1.3 cm in width. Therefore, in Korea, this species can be distinguished from the three genera (Oryza, Leersia, Zizania) of the tribe Oryzeae that lack glumes and bear spikelets arranged in a panicle. Among these genera, Zizania is significantly different from Chikusichloa with its much greater plant height (150–250 cm) and its spikelets with unisexual florets. Leersia is superficially similar in having spikelets with bisexual florets, but it is distinguished by its sessile florets and the presence of three or six stamens. A comparison of the four genera recorded in Korea is provided in Table 1.

Chikusichloa aquatica is similar to Molinia japonica in overall appearance from a distance and occurs in a similar habitat in Korea. However, C. aquatica can be distinguished by its smooth leaf sheaths, reduced glumes, and lanceolate lemmas with five veins. In contrast, M. japonica possesses hairy leaf sheaths, well-developed three-veined glumes, and lemmas lacking veins, which clearly separate it from C. aquatica.

Chikusichloa aquatica grows in a small, muddy pond with a small stream flowing through its center in the lowlands of Minoreum, Jejudo Island. This small pond measures approximately 30 × 10 m, and C. aquatica colonies occupy most of the area, growing along the edges. Based on our observations, individual plants grow to a width of 40–50 cm, and the number of individuals is confirmed to be approximately 300.

Chikusichloa aquatica is rarely distributed in Japan and its population is small, so it is designated as vulnerable (VU) on the Red List (Ministry of the Environment in Japan, 2025). In China, this species is also protected and categorized endangered (EN) (Qin et al., 2017). This is the first time that its distribution area has been confirmed in Korea, and it will be necessary to accumulate information on C. aquatica through distribution research in similar environments in the future.

The new Korean name given is ‘Han-san-i-seul-sae,’ based on the characteristic shape of the swollen spikelets that resemble dewdrops and in honor of the late Hansan Bu Jong Hyu, who was devoted to the plants on Jejudo Island.

The following key to the related Korean tribe Oryzeae genus has been prepared for all species on the Korean Peninsula.

Key to the genus in tribe Oryzeae in Korea

1. Spikelets with unisexual florets ·············· Zizania 줄속
1. Spikelets with bisexual florets.
- 2. Spikelet with 2 narrow scales below the floret ···························································· Oryza 벼속
- 2. Spikelet without scales below the floret.
  - 3. Spikelets laterally compressed; florets sessile; stamen 3 or 6 ·································· Leersia 겨풀속
  - 3. Spikelets nearly terete; florets stipitated; stamen 1 ···································· Chikusichloa 이슬새속

NOTES

ACKNOWLEDGMENTS

This work was supported by a grant from the Sixth National Ecosystem Survey of the National Institute of Ecology (NIE) funded by the Ministry of Environment (MOE) of the Republic of Korea (NIE-A-2025-01).

CONFLICTS OF INTEREST

The authors declare that there are no conflicts of interest.

Fig. 1

Chikusichloa aquatica on Jejudo Island of Korea: A. Habitat. B. Habit. C. Basal culm and rhizome. D. Inflorescence. E. Portions of inflorescence. F. Ligule. G. Spikelets. H. Floret stipe. I. Lemma. J. Palea. K. Caryopsis (photo by M.O. Moon and J.H. Kim).

Fig. 2

The voucher specimen of Chikusichloa aquatica collected from Minoreum on Jejudo Island (photo by S.S. Choi).

Table 1

Comparison of several major characteristics of the tribe Oryzeae in Korea.

Characters	Oryza	Leersia	Chikusichloa	Zizania
Height of culms (cm)	60–120	35–100	60–140	150–250
Width of leaf blades (mm)	5–8	3–12	6–13	20–30
Sexuality of spikelets	Bisexual	Bisexual	Bisexual	Unisexual
Floret attachments	Sessile	Sessile	Stipitate	Stipitate
No. of stamens	6	3–6	1	6
Caryopsis shape	Oblong	Oblong	Fusiform	Cylindrical

Based on Cho et al. (2016) and our own measurements.

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A new generic record of Chikusichloa (Poaceae) for the flora of Korea