The genus Boehmeria Jacq. (Urticaceae) comprises approximately 100–150 species and is widely distributed across tropical and subtropical regions (Wang, 1981a; Yahara, 1981; Chen et al., 2003; Wilmot-Dear and Friis, 2013). The genus is distinguished from related genera by plants without stinging trichome, inflorescence without involucre, staminate flowers with 3–5 stamens, inflexed filaments, pistillate flowers with tubular perianth, filiform stigma, remaining perianth of the achene, etc. (Chen et al., 2003; Kim and Sun, 2018). Based on morphological characteristics, including phyllotaxis, leaf margin shape, achene shape, and trichome, Satake (1936) recognized two subgenera and seven sections. Later, Wang (1981a, 1981b, 2016) degraded these to section or series rank by habit, leaf apex shape, inflorescence shape, and achene shape, and treated five sections. Although the morphological characteristics of the leaves are highly variable, the shape, margin, trichome, and texture of leaves are known to be important characters in the current classification systems (Satake, 1936; Wang, 2016; Jo, 2023).

Approximately 12–14 taxa of Boehmeria are known to be distributed in Korea (Kim and Sun, 2018; Korea National Arboretum, 2023). Recently, Jo et al. (2021) recognized two unrecorded species, B. gracilis C. H. Wright and B. silvestrii (Pamp.) W. T. Wang. In the Korean Boehmeria, B. hirtella Satake, B. nakaiana Satake, B. quelpaertensis Satake, and B. taquetii Nakai have been considered as endemic species in Jejudo Island, Korea (Lee, 1996). However, Jo (2023) recently treated B. nakaiana and B. taquetii as newly additional synonyms of B. sieboldiana Blume, and B. hirtella and B. quelpaertensis were also confirmed to be distributed in Japan. Therefore, he did not consider these two species as Korean endemic species. In conclusion, Korean Boehmeria was classified into a total of 13 species within two sections: sect. Tilocnide and Duretia, and three series: ser. Longispicae, Sieboldianae, and Spicatae in sect. Duretia (Jo, 2023).

While studying the genus Boehmeria collected in South Korea, we firstly confirmed the identity of B. nakashimae Yahara, which is known as an endemic species in Japan, on Jejudo Island. This species is distributed along the coast of northern Kyushu in Japan (Yahara, 1983a, 1983b). It was first recognized as a hybrid of B. hirtella and B. holosericea Blume (Yahara, 1983a). Yahara (1983a, 1983b) distinguished B. holosericea by leaves with a serrulate margin, a subcaudate-acuminate apex, and sterile staminate flowers. Unlike B. hirtella, B. nakashimae has large, thick leaves and dense trichomes on the stem, petiole, and leaf veins. Yahara (1983a) recognized as a triploid taxon reproducing by apomixis. Therefore, B. nakashimae is treated as a species rather than as a hybrid.

In this study, we used scientific names and Korean names of Boehmeria based on the recently updated Checklist of Vascular Plants in Korea (Korea National Arboretum, 2023). These scientific names had no nomenclatural problems, and this study focused on taxa with confirmed identities. We morphologically compared two closely related series, ser. Sieboldianae (including B. nakashimae) and ser. Longispicae, and have presented a key for taxa within these two series. Furthermore, descriptions, photographs, and illustrations of B. nakashimae are provided.

Boehmeria nakashimae Yahara, J. Jap. Bot. 58: 88, 1983 (Figs. 1, 2).—TYPE: Japan. Kyushu, Fukuoka Pref., Fukuoka City, Shikanoshima, 19 Sep 1937, K. Nakashima 15-a (holotype: TI!, barcode TI00082084; isotypes: “Nakashima 15-b,” TI!, barcode TI00082085, “Nakashima 15-c,” TI, not seen) (Fig. 3).

Korean name: Je-ju-top-mo-si-pul (제주톱모시풀).

Herbs perennial, monoecious or dioecious. Stems lignified at fruiting, erect to descending, deeply sulcate, 1.2–2.0 m tall, 3.2–6.2 mm in diam., yellow-green, densely strigillose; piths not hollow. Leaves opposite, pairs subequal in size; stipules interpetiolar, free, reflex, caducous, lanceolate, 13.3– 15.2 × 4.5–5.9 mm, yellow-green, sparsely strigillose on the adaxial surface, sparsely strigillose on the abaxial surface, densely strigillose on the vein; petioles 6.1–14.0 cm long, 1.7–2.7 mm in diam., yellow-green, densely strigillose; middle leaf blades ovate to broadly ovate, elliptic-ovate, or sub-orbicular, 19.6–27.0 × 11.3–25.5 cm, base rounded, broadly cuneate, or cordate, margin serrulate-dentate, uniform, teeth 17–29 on one side, apex unlobed, short caudate or narrowly acute, adaxial surface green or yellow-green, densely strigillose, densely punctiform lithocysts with cystoliths, midvein flat, abaxial surface yellow-green, densely strigillose along midvein, densely hirsutulous along veinlets, chartaceous. Inflorescences axillary, spicate with glomerules; staminate inflorescences branched on middle part of stem, 10.3–14.9 cm long; pistillate inflorescences often branched or unbranched on upper half part of stem, 10.7–19.8 cm long, glomerules dense at flowering. Flowers unisexual; staminate flowers 4-merous, 4.4–5.9 mm wide; pedicels 0.3–0.6 mm long, yellow-green; perianth lobes cleft near to the middle, convex, elliptic, 1.1–1.4 × 0.8–1.1 mm, without appendages, yellow-green, strigillose in outside; filaments linear, inflexed, 1.6–2.5 mm long, yellow-green, anthers basifixed, 0.7–0.9 × 0.6–0.9 mm, white; ovary rudimentary, clavate; pistillate flowers 2.2–3.3 mm long, sessile; perianth tubes rhomboid to obovoid, 1.0–1.5 × 0.5–1.1 mm, yellow-green, strigillose; necks 2-lobed; style 1, linear, plumose, 1.2–1.9 mm long, white, stigma linear. Infructescences glomerules dense at fruiting, 3.8–5.4 mm wide. Achenes 32–119 per glomerule, rhomboid to obovoid to sub-orbicular, winged, 1.9–2.3 × 1.0– 1.4 mm, base cuneate or obtuse, strigillose.

Chromosome number: 2n = 42 (Yahara, 1983b).

Phenology: Flowering July to September, Fruiting September to November.

Distribution: Korea (Jejudo Island), Japan (Northern Kyushu and Shikoku) (Fig. 4).

Habitat: This species inhabits half-shaded mesic places along forest edges near seashores (Tateishi, 2006). It is also found at 200–900 m in Oreums and along roadsides on Jejudo Island.

Additional specimen examined: JAPAN. Shikoku: Kouchi Pref., Awa Susaki City, Awa-kaigan, 8 Nov 2012, T. Miyazaki 1211201 (PE); Kouchi Pref., Ootuki Town, Between Tomaru-ura and Tachibana-ura, 7 Oct 2003, T. Miyazaki 310152 (L).

KOREA. Jeju-do: Jeju-si, Aewol-eup, Bongseong-ri, Handae Oreum, 21 Oct 2021, H. J. Jo et al. HJ211021-002, 003 (ANH); Hallim-eup, Hyeopjae-ri, Biyangdo Island, 26 Jul 2022, H. J. Jo et al. HJ220726-002–004 (ANH); Hallim-eup, Mundoji Oreum, 19 Sep 2019, H. J. Jo et al. HJ190919-001 (ANH); 16 Jun 2021, H. J. Jo et al. HJ210616-001–003 (ANH); Jocheon-eup, Banong Oreum, 29 Jul 2021, H. J. Jo et al. HJ210729-001 (ANH); Seogwipo-si, Hawon-dong, 15 Sep 2020, H. J. Jo et al. HJ200915-003–005 (ANH); Sallongnam-ro, 1115, 20 Aug 2020, H. J. Jo et al. 200820-007 (ANH), 24 Aug 2022, H. J. Jo et al. HJ220824-004 (ANH).

Taxonomic note: At the habitats of B. nakashimae investigated in this study, B. holosericea and B. hirtella, which were previously recognized as parent species (Yahara, 1983b), were not found. Especially, B. holosericea is geographically isolated from B. nakashimae and is only found along the coast. Boehmeria nakashimae is most similar to B. holosericea in terms of the middle leaf shape. However, the two species differ in morphological characteristics such as leaf margin, appendages of staminate flowers, and achene trichomes (Table 1, Figs. 1, 2, 5). Boehmeria nakashimae is also distinctly distinguished from its related species, B. hirtella and B. sieboldiana, by morphological characteristics such as a deeply sulcate stem, a more densely strigillose stem, and a strigillose perianth of staminate flowers (Table 1, Figs. 1, 2, 5).

Wilmot-Dear and Friis (2013) mentioned that B. nakashimae could be an intermediate form between B. holosericea and B. japonica (L. f.) Miq. However, in this study, we confirmed that this species reproduces through apomixis. Yahara (1983a) also recognized it as a triploid species reproducing by apomixis. In addition, this species is clearly distinguished from B. japonica and B. platanifolia (Maxim.) C. H. Wright by its plant trichomes, leaf margin shape, leaf apex shape, and achene trichomes (Table 1, Figs. 1, 2, 5). Therefore, the new Korean name, ‘Je-ju-top-mo-si-pul’ was given based on its serrulatedentate leaf margin and geographical distribution in Korea.