Viola tenuis Benth.

Viola tenuis Benth. in London J. Bot. 1: 482 (1842) Fig. 2 ≡ Viola diffusa subsp. tenuis W. Becker in Philipp. J. Sci. 19 (6): 714 (1921). Type. China • Hong Kong, 1841, Hinds s. n. (holotype: K 000370141 [photo!]). Additional specimens examined. China • Hong Kong, Sai Kung, 06 May 2016, Danial Hang HKY 0012 (KFBG, Fig. 3 c); • Hong Kong, Sai Kung, 13 Mar 2018, Jingang Liu JG 0615 (KFBG, Fig. 3 b); • Hong Kong, Sai Kung, 21 Jul 2023, Jinlong Zhang JL 1488 (KFBG); • Zhuhai, Dawanshan Island, 07 Nov 1973, Yue 73 73-3160 (IBSC); • Zhuhai, Dawanshan Island, 04 Nov 1973, Yue 73 73-3055 (IBSC); • Zhuhai, Dangan Island, 12 Jul 2017, Ming Tan Tu TY 3390 (CDBI); • Shenzhen, Qiniangshan Mountain, 18 Mar 2005, Shouzhou Zhang & Liangqian Li 0259 (SZG); • Shenzhen, Qiniangshan Mountain, 17 May 2005, Shouzhou Zhang & Liangqian Li 1528 (SZG); • Shenzhen, Qiniangshan Mountain, 16 Apr 2005, Shouzhou Zhang & Liangqian Li 0196 (SZG); • Shenzhen, Qiniangshan Mountain, 16 Apr 2019, Q. Fan 18910 (SYS); Etymology. It is hypothesised that the specific epithet refers to the plant’s thin rhizomes. Vernacular name. We propose a Chinese name, Xì Jīng Jǐn Cài (细茎堇菜), to reflect the thin rhizomes of this species. Description. Perennial, stoloniferous herb with basal leaves rosulate, 5–8.5 cm tall. Rhizome erect or obliquely erect, rather slender, dark purple, with dense remains of stipules and petioles. Lateral stolons purple or light green, spreading and elongating, usually producing adventitious roots, with an apical rosette of leaves. Stipules ca. 8 mm, adnate to petioles for about 1 / 3 of their length at base, linear-lanceolate, acute at apex, with margins pinnatifid, glabrous or rarely puberulous. Petioles 2–4 cm, with wings narrow, glabrous or sparsely puberulous along the margin. Leaf blades ovate or ovate-oblong, 1.0–2.4 × 1.5–3.3 cm, glabrous or densely puberoulous; margin finely crenate; base wedge-shaped to truncated; apex obtuse, rarely acuminate. Chasmogamous flowers ca. 1.5 cm in diam.; peduncles slender, 6–7 cm long, glabrous, much higher above the basal leaves, with two opposite bracteoles above middle; bracteoles linear-lanceolate, ciliate, 5.5–6 mm long, apex acuminate or obtuse. Sepals green, ciliate, lanceolate, 1.5–1.7 × 4–5.5 mm, with entire margin, acuminate apex and truncate, with extremely short semicircular appendages. Petals purple, anterior one with apparent violet lines, posterior and lateral ones with a yellow to green patch at base; posterior petals, narrowly ovate to oblong, 4.5 × 12 mm, glabrous, with entire margin and obtuse apex; lateral petals with straight to slightly clavate hairs at the base, oblong, ca. 1.3 cm long, with entire margin, apex obtuse; anterior petal spatulate, 8 mm long, with a short, round spur, interior side of the spur puberulent. Stamens 5, unequal, puberulent; anther thecae ca. 0.9 mm long, with terminal appendages ca. 0.6–0.85 mm long; posterior appendages (nectar spurs) of the two anterior stamens ca. 0.95 mm long, triangular. Ovary ovoid, ca. 1.25 × 1.49 mm, glabrous; style clavate, ca. 1.35 mm long, conspicuously geniculate at base; stigma glabrous, with thickened lateral margins, shortly beaked at apex. Cleistogamous flowers ca. 3.2 mm long; peduncles ca. 6.5 mm long; bracteoles linear-lanceolate, puberulous, ca. 2.8 mm long, apex acute. Sepals green, glabrous or puberulous, lanceolate, ca. 0.8 × 3.2 mm, with entire margin, acuminate obtuse. Capsules glabrous, light green to yellow, ovoid to oblong, ca. 9 mm long. Seeds brown, oblongoid, ca. 1.4–1.55 mm long, with tubercles and inconspicuous elaiosomes. Phenology. Chasmogamous flowers from April to May, rarely October, cleistogamous flowers from May to September and fruits from April to October. Distribution and habitat. Viola tenuis is currently known from Hong Kong, Shenzhen and Zhuhai in China (Fig. 4). The species grows on rocks or in rocky crevices at altitudes of 100–700 m a. s. l. Conservation status. As its area of occupancy is estimated less than 20 km 2, the conservation status of Viola tenuis should be considered as Vulnerable (VU) according to IUCN Red List criteria (D 2; IUCN 2024).