Isodon villosus Y.P. Chen & H. Peng, 2016

Chen, Ya-Ping, Xiang, Chun-Lei, Sunojkumar, Purayidathkandy & Peng, Hua, 2016, Isodon villosus (Nepetoideae, Lamiaceae), a new species from Guangxi, China, Phytotaxa 268 (4), pp. 271-278 : 272-275

Isodon villosus Y.P. Chen & H. Peng , sp. nov. (figs. 1–2)

S imilar to I. lophanthoides (Buch.-Ham. ex Don 1825: 110) Hara (1985: 235) and I. phyllopodus ( Diels 1912: 227) Kudô (1929: 135) (fig. 3), but differs from the former in its calyx 2-lipped to 1/2 its length (vs. to 1/3 its length in I. lophanthoides ), corolla tube declinate (vs. straight in I. lophanthoides ), stamens and style included (vs. long-exerted in I. lophanthoides ), as well as mericarp 1.4 × 0.9 mm (vs. 0.9 × 0.7 mm in I. lophanthoides ), differs from the latter in its base of lamina not decurrent on petiole (vs. base of lamina decurrent on petiole in I. phyllopodus ), panicle densely septate-villose (vs. sparsely pubescent in I. phyllopodus ), as well as posterior lip without spot (vs. with bluish-purple spots in I. phyllopodus ).

Type:— CHINA. Guangxi: Hezhou, Babu District, Gupo Mountains, among the grass and shrubs, elevation 1690 m, 24°38 ′ 07 ″ N, 111°30 ′ 51 ″ E, 19 September 2015, Y. P. Chen EM 227 (holotype KUN!, isotypes A!, K!, KUN!, NSW!, PE!, W!).

Perennial herbs, 30–80 cm tall. Rhizomes woody, tuberose. Stems erect to ascending, branched, quadrangular, 4- sulcate, densely septate-villose. Leaves opposite; petioles 1–4 mm long; laminas 5–7 × 5–6 cm, chartaceous, broadly ovate, apex obtuse, base broadly cuneate to shallowly cordate, margin creneate, adaxially olive green, densely septate-hirtellous, abaxially light green, septate-villose on veins, densely red-brown glandular. Panicles terminal and axillary, 5–10 (–15) × 1.5–3 cm, cymes 5–11-flowered, densely septate-villose and glandular puberulent, pedunculate; lower floral leaves similar to cauline leaves but smaller and sessile, upper ones gradually change into sessile bracts; bracteoles ovate to linear, 2–5 mm long; peduncles 2–5 mm long, pedicels 1.5–4 mm long. Calyx campanulate, 1.5–2 mm long, 1.5–2 mm in diameter at mouth, densely septate-villose on veins and glandular puberulent, dotted with red-brown glands, 2-lipped to 1/2 its length; teeth 5, ovate, apex obtuse; fruiting calyx dilated, 4–4.5 mm long, obviously nervate. Corolla white, declinate, 7–8 mm long, septate-villose and red-brown glandular outside; tube ca. 3 mm long, 2–2.5 mm in diameter, saccate abaxially near base; 2-lipped, posterior lip 4-cleft, 3.5–4 mm long, reflexed, lobes oblong, anterior lip 4–5 mm long, suborbicular, concave. Stamens 4, included. Style equally 2-cleft at apex, included. Mericarps compressed-ovate, ca. 1.4 × 0.9 mm, brown, smooth, glabrous.

Distribution and Habitat: — Since no more material of I. villsosus is found except for the type specimens, the new species is now only known from the National Forest Park of Gupo Mountains in Guangxi Zhuang Autonomous Region, southern China. Isodon villosus grows among the grass and shrubs along the hiking trail at an elevation between 2400 m and 2700 m. Although it is abundant on the top area of the Gupo Mountains, its habitat is endangered by the increasing number of tourists and hikers. More field work is needed to further elucidate its habitat and distribution area.

Phenology: — Flowering from July to September, and fruiting from August to October.

Etymology: — The epithet of the new species refers to its densely septate-villose panicles.

Notes: — Because I. villosus is characterized with red-brown glands, it may be a member of Clade I according to Yu et al. (2014). Morphologically, I. villosus is most similar to I. lophanthoides and I. phyllopodus (fig. 3), which are also from Clade I.

The characters we chose to distinguish the three species tend to be stable in variation and useful for the species delimitation within Clade I. Detailed differences among the three species are summarized and listed in Table 1, and their distribution in China based on herbarium specimens and our own collections (see Appendix 1) is shown in fig. 4.

Isodon lophanthoides (fig. 3A–C) is one of the most variable and widely distributed species of the genus. It can be found in southern China, India, Nepal, Bhutan, Bangladesh, Burma, Laos, Thailand, and Vietnam, and thrives in forests, on grassy slopes, at paddies, roadside, and streamside at an elevation of 400–3000 m ( Wu & Li 1977, Li 1988, Li & Hedge 1994, Suddee et al. 2004). Plants of both I. villosus and I. lophanthoides are red-brown glandular and leaves are broadly ovate and without alate pseudopetiole, however, the two species can be distinguished by morphology of corolla tube, posterior lip of corolla, and stamens and style, length of anterior lip of corolla, and size of mericarp ( Table 1).

Isodon phyllopodus (fig. 3D–F) is restricted to southwest China (Guizhou, Sichuan, and Yunnan) and occurs in thickets, on grassy slopes, at the margin of forest and roadside from 2100 m to 3000 m ( Wu & Li 1977, Li 1988, Li & Hedge 1994). Isodon villosus shares red-brown glandular plants, declinate corolla tube, and included stamens and style with I. phyllopodus , but they differ from each other in existence of alate pseudopetiole, indumentum on panicles, and morphology of posterior lip of corolla ( Table 1).

An identification key for 15 taxa of Isodon distributed in Guangxi is here provided.