Introduction
Poaceae Barnhart, grass family, is a large group of monocotyledonous flowering plants belonging to the order Poales (Kellogg, 2015). This family comprises 789 genera and 11,783 species worldwide and is a large taxon consisting of 12 subfamilies and 54 tribes taxonomically (Soreng et al., 2022). There are approximately 109 genera and 348 species (Kim et al., 2019), including alien plants in Korea. Poaceae plants are generally useful to humans and animals as cereal crops, dried fodder, and green herbage (Farouk et al., 2023).
Arthraxon P. Beauv., is a small genus belonging to the tribe Andropogoneae of family Poaceae (Arthan et al., 2017; Chen and Phillips, 2006; Lee, 2018; Van Welzen, 1981, including 24 species in the Old World (Chen and Phillips, 2006; WFO, 2025), and most species of Arthraxon are native to tropical and subtropical regions of the Eastern Hemisphere (WFO, 2025). Arthraxon plants are annual or perennial herbs with procumbent branches of which the terminal parts ascend (Van Welzen, 1993), and usually small leaves, ovate, obcordate, subamplexicaul at base, the subdigitate panicles, the laterally compressed spikelets and the upper lemma with its geniculate, subbasal awn (Van Welzen, 1993). In Korea, only one species in the genus Arthraxon is reported; A. hispidus (Kim et al., 2018; Korea National Arboretum, 2011; Lee, 2018).
Recently, unrecorded species continue to be reported in Korea (Choi et al., 2024). During a plant diversity field survey in Korean Peninsula, an unrecorded species, Arthraxon prionodes was discovered in rocky mountain slopes from Chungcheongnam-do, Korea. We provide precise description, taxonomic key to Korean Arthraxon species, voucher specimens and photographs of its habit (Figs. 1, 2).
Materials and Methods
The Arthraxon prionodes was collected from Chungcheongnam-do, Korea. The morphological characters of the species were examined based on the reference by Chen and Phillips (2006), using live specimens and photographs (Figs. 1, 2). In addition, keys of Korean Arthraxon followed (Cho et al., 2016; Kim et al., 2018; Korea National Arboretum, 2011; Lee, 2018). Photographs in the field were captured by using a digital camera (Body: Nikon D750, Tokyo, Japan; Lens: Nikon 60 ㎜ f/2.8D, Tokyo, Japan). Measurements of the morphological characters were performed by using digital Vernier calipers (Mitutoyo, CD-20AX, Sakado, Japan), and data derived from field notes. All voucher specimens were deposited at the herbarium of National Institute of Biological Resources (KB).
Taxonomic Treatment
Arthraxon prionodes (Steud.) Dandy, Fl. Pl. Sudan 3: 399. 1956; Andropogon prionodes Steud., Syn. Pl. Glumac. 1: 383. 1854. -Type: Ethiopia. Tigray, 12 Nov 1838, Schimper, 1117 (Lectotype: P, 00440282, photo!; designated by Van Welzen (1981: 283); Isolectotype: MO, 1660919, photo!).
Korean name: 큰조개풀 (Keun-jo-gae-pul).
Herbs perennial. Rhizome short, knotty, covered by silky scales. Culms loosely tufted, wiry, erect or trailing, 40-60 ㎝ tall. Leaves cauline; leaf she aths glabrous or tuberculate-hispid; leaf blades narrowly lanceolate to ovate, tough, glaucous, 2-7 ㎝ × 5-15 ㎜, usually glabrous, base rounded, margins pectinate-setose, apex setaceously acuminate; ligule ca. 0.5 ㎜ long, eciliate membrane. Inflorescences compound racemes, digitate, open. Racemes pale green or pale purple, 2-8, 4-7 ㎝ long, subsessile; rachis internodes 2-3 ㎜ long, shorter than the spikelet, pilose. Spikelets paired; Pedicelled spikelets 4-5 ㎜ long, narrowly lanceolate, staminate. Sessile spikelet 5-6.5 ㎜ long, linear to narrowly lanceolate, lower glume lanceolate, chartaceous, strongly convex, laterally 2-keeled, margins inflexed, back obscurely veined below middle, glabrous or puberulous, rarely shortly pubescent, 5 scaberulous veins between keels toward apex, keels stoutly tuberculate-spinose; upper glume lanceolate, chartaceous, 1-keeled, keeled above, apex acute. Lower floret sterile; lemma oblong, 4-5 ㎜ long, veins 2, hyaline, apex obtuse; palea absent. Upper floret bisexual; lemma lanceolate, 5-6.5 ㎜ long, vein 1, hyaline, awned at base; awn 0.8-1.5 ㎝ long, with twisted column; palea absent or minute; Stamens 3, anthers 2.5-3.5 ㎜ long.
Phenology: flowering August to September and fruiting September to October.
Habitat: rocky mountain slopes, streamsides, roadsides.
Distributions: Northeast and East Tropical Africa, Arabian Peninsula, Afghanistan, China, Peninsula Malaysia (POWO, 2025), and Korea.
Voucher specimens: Korea. Chungcheongnam-do: Geumsan-gun, Nami-myeon, Daeyang-ri, 01 Sep 2020, Yang-Hoon Cho & Seok-Soon KimCN200046, CN200047 (KB); ibid., 01 Sep 2022, Jung-Hyun KimKIMJH22109 (2 sheets), KIMJH 22110 (2 sheets), KIMJH22111 (2 sheets), KIMJH22112 (2 sheets) (KB); ibid., 05 Sep 2023, Jung-Hyun Kim KIMJH 23351 (2 sheets), KIMJH23352 (3 sheets) (KB); ibid., 29 Aug 2024, KIMJH24387 (3 sheets), KIMJH24388 (3 sheets), KIM JH24389 (3 sheets) (KB).
Note: Arthraxon prionodes was known to be distributed in Northeast and East Tropical Africa, Arabian Peninsula, Afghanistan, China and Peninsula Malaysia (POWO, 2025). From this study, the new natural distribution is discovered at rocky mountain slopes in Geumsan-gun, Chungcheongnam-do, Korea. Two populations were composed of ca. 10 individuals within 5 × 3 ㎡ in size. The elevation of both of these population sites ranges from ca. 450 to 470 m a.s.l. This species is discovered under the trees (e.g., Ulmus davidiana var. japonica (Rehder) Nakai and Rhus javanica L.), shrub (e.g., Lespedeza cyrtobotrya Miq.), and vines (e.g., Clematis apiifolia DC., Pueraria lobata (Willd.) Ohwi, and Paederia foetida L.), together with other herbaceous plants, such as Chamaecrista nomame (Siebold) H. Ohashi, Artemisia indica Willd., Crepidiastrum denticulatum (Houtt.) Pak & Kawano, Commelina communis L., Arundinella hirta var. ciliata (Thunb.) Koidz. Eragrostis ferruginea (Thunb.) P. Beauv., Oplismenus undulatifolius (Ard.) Roem. & Schult., Setaria faberi R. A. W. Herrm., and Spodiopogon sibiricus Trin.
A key to Korean Arthraxon species
1. Plants annual; lower glume of sessile spikelet without lateral keels, margins flat; stamens 2 A. hispidus 조개풀
1. Plants perennial; lower glume of sessile spikelet laterally 2-keeled, margins inflexed; stamens 3 A. prionodes 큰조개풀
