Rubia pianmaensis R. Li & H. Li, 2013

Li, Rong & Li, Heng, 2013, A new species of Rubia (Rubiaceae) from western Yunnan, China, Phytotaxa 140 (1), pp. 51-55 : 51-54

Rubia pianmaensis R. Li & H. Li , sp. nov. ( Fig. 1 )

Species Rubiam siamensem Craib affinis , sed stipulae majores, ad 1.5–5.5 × 1.7–4.5 cm, flores 5-6-meris, inflorescentiis brevis, 3–5 cm longi differt.

Type: — CHINA. Yunnan: Lushui County, Pianma township, Ganheluo , 8.5 km SE of Pianma, subtropical evergreen broad-leaved forest disturbed by felling and clearing, growing along the roadside in forest undercanopy, 2160 m, 26°02′55″N, 98°36′51″E, 13 May 2005, Gaoligong Shan Biodiversity Survey 22830 (holotype KUN!, isotypes CAS!, E!) .

Climbing vines, herbaceous; stems 3–5 m long, green to dark purple, quadrangular, inconspicuous 4-ribbed when dried, 3–4 mm in diameter, glabrous. Stipules large, sessile, green, persistent, broadly ovate, 1.5–5.5 × 1.7–4.5 cm, glabrous, apex acute, base obtuse, secondary veins 7–9 each side. Leaves opposite; petioles green to dark purple, 2–4.5 cm long, retrorsely aculeolate; blades ovate to narrowly ovate, 4.5–14 × 2.5–6.5 cm, papyraceous, base cordate, apex acuminate to long acuminate, sometimes falcate, green adaxially, light green abaxially, glabrous on both surfaces, retrorsely aculeolate along the principal veins, margins aculeolate; secondary veins 5 each side, palmate, impressed adaxially, lateral veins inconspicuous. Inflorescences thyrsoid, paniculate, 3–5 cm long, with terminal and axillary, 2-3-flowered cymes; axes glabrous and smooth; bracts 2 or 4, leaf-like, green, broadly ovate to narrowly ovate, ca. 0.6–5 × 0.5–1.4 cm, apex acuminate, glabrous; bracteoles 2, green, narrowly oblong, ca. 3 mm long; pedicels green, ca. 2–3 mm long, glabrous. Calyx tube subglobose, green, ca. 1 mm, glabrous. Corolla pale yellowish-green, turning light green when dried, rotate, glabrous on both surfaces, 5-6-lobed, corolla tube ca. 1 mm long, lobes ovate, ca. 1.5–2 × 1 mm, apex acuminate; stamens 5-6, alternate with corolla lobes, inserted on corolla tube, exserted, filaments green, ca. 1 mm, anthers sub-oblong, yellow to yellowish-brown, ca. 1 mm; style light green, ca. 1 mm long, stigma capitate, 2-lobed; ovary 2-locular with 1 ovule per locule.

Distribution and habitat: — Rubia pianmaensis is currently known only from three sites of the type locality in Pianma township, Lushui County, Yunnan Province, China. It grows along the trail under the subtropical evergreen broad-leaved forest, on limestone and decomposed granite, at 1600–2300 m elevation.

Conservation status: —The species has been collected only from the type locality and is therefore assumed to be rare. It is considered as ‘Endangered’ (EN) using the criteria set out by IUCN (2001) as its known area of occupancy is less than 500 km 2 (criterion B2) and the total population size is estimated to be smaller than 2500 mature individuals (criterion C).

Phenology: — Rubia pianmaensis was observed with flowers in May.

Etymology: —The specific epithet of the new species refers to its type locality.

Discussion: —According to Chen & Ehrendorfer (2011), Luo (1999), and Pojarkova’s (1958) monographic works, Rubia pianmaensis obviously belongs to the Rubia siamensis group within Rubia sect. Oligoneura Pojarkova (1958: 386) . The section is characterized by the leaves with 3-11 palmate veins. The Rubia siamensis group is a well-defined group from SW China (Sichuan, Yunnan) and N Thailand (Chiengmai), which is characterized by the opposite leaves and the typical (not leaf-like) interpetiolar stipules ( Chen & Ehrendorfer 2011). Morphologically, the new species is similar to Rubia siamensis Craib (1911: 397) ( Fig. 2 ), but differs by having larger stipules, 5-6-merous flowers, and the shorter inflorescences. The major differences between the two species are outlined in Table 1.

Additional specimens examined (paratypes): — CHINA. Yunnan: Lushui County, Pianma township, Wuzhong , 2300 m, 03 August 1964, S. G. Wu 8348 ( KUN) ; Pianma township, Ganheluo , 8.5 km SE of Pianma, 2160 m, 26°02′55″N, 98°36′51″E, 13 May 2005, Gaoligong Shan Biodiversity Survey 22828 ( CAS, E, KUN) ; Pianma township, Gangfang, near the China-Burma border, 1600 m, 25°07′22″N, 98°34′31″E, 18 May 2005, Gaoligong Shan Biodiversity Survey 23364 ( CAS, E, KUN) ; Pianma township, Ganheluo, 8.5 km along the road from Pianma to Gangfang , 2150 m, 25°02′55″N, 98°36′51″E, 18 May 2005, Gaoligong Shan Biodiversity Survey 23393 ( CAS, E, KUN) ; Pianma township, Gangfang, 13 km along the road from Pianma to Gangfang , 2150 m, 26°03′37″N, 98°36′34″E, 13 May 2005, Gaoligong Shan Biodiversity Survey 24048 ( CAS, E, KUN) ; Pianma township, Gangfang , 17 km N of Pianma, 2253 m, 26°03′29″N, 98°36′26″E, 17 May 2005, Gaoligong Shan Biodiversity Survey 24395 ( CAS, E, KUN) .

Figures

FIGURE 1. Rubia pianmaensis. A. Flowering branch. B. Node with leaves and stipules. C. Stipule. D. Flower (5-merous). E. Flower (6-merous). F. Dissected corolla showing stamens. G. Ovary and style. Drawn by Rongmei Zhang from the holotype.

FIGURE 2. Rubia siamensis. A. Fruiting branch. B. Stipule. Drawn by Rongmei Zhang. Voucher: Gaoligong Shan Biodiversity Survey 21831 (KUN).