Ceropegia tribounii Kidyoo, 2015

Kidyoo, Manit, 2015, Ceropegia tribounii (Apocynaceae, Asclepiadoideae), a new species from western Thailand, Phytotaxa 205 (1), pp. 59-64 : 59-64

Ceropegia tribounii Kidyoo , sp. nov. ( Fig. 1 & 2 )

Ceropegia tribounii differs from C. anjanerica by having sessile, linear-lanceolate leaves, broadly obovate corolla with lobes shorter than the corolla tube and trichomes on the inner faces of the interstaminal corona.

Type:— THAILAND. Tak: Tha Song Yang district, in the mountains near Thi Mo Bo waterfall, 700 m elevation, 4 August 2013, M. Kidyoo 1608 (holotype, BCU!, isotype, BKF!).

Herbs, erect, perennial, with usually a single stem only, not twining, with clear latex in all parts. Rootstock tuberous; tubers subglobose, smooth, light brown, 1.1–2 cm in diam.; roots fibrous. Stem usually unbranched, terete, pubescent, 20–30 cm tall, 1.5–2.2 mm in diam., green when young, turning brown with age; internodes 1–3.5 cm long. Leaves opposite, decussate, sessile; blade linear to linear-lanceolate, 4–8.5 × 0.25–0.5 cm, slightly carinate in cross section, coriaceous, base attenuate, margins entire, slightly revolute, apex acute to acuminate; abaxial surface pale green, glabrous, adaxial surface green, glabrous; midrib greenish white, slightly convex; lateral veins obscure. Flowers solitary, extra-axillary; sessile; pedicel pinkish white, 5–8 mm long, 1–1.5 mm in diam., glabrous; bract solitary, attached at base of pedicel, lanceolate, ca. 0.8 × 0.3 mm, pinkish white, apex acute. Sepals yellowish green or green, narrowly lanceolate, 4.5–5.5 × 0.5–0.8 mm, glabrous, apex sharply acute. Corolla tubular-urceolate, upright, straight to slightly curved; corolla tube yellow to yellowish white with five purple lines alternate the sepals, glabrous, 2–2.3 cm long, base slightly inflated to a narrow ovoid shape, 0.6–0.8 cm in diam., then above the inflation, tube becoming straight and gradually narrowing to an ascending cylindrical portion 0.6–0.8 cm in diam.; interior of inflated part purple with dark purple lines inside, glabrous; corolla lobes yellow, speckled yellowish brown at apex, broadly obovate, 1.7–1.9 × 0.7–0.8 cm, apex shortly acuminate, connate at tips, outside glabrous, inside pubescent with short white trichomes, margins strongly reflexed in medium region. Gynostegium stipitate, stipe 0.7–0.8 mm long, 1.3–1.5 mm in diam. Gynostegial corona double, interstaminal lobes joined to form a shallow cup, 4–4.5 mm in diam., purple, shortly pilose inside, apex of lobes minutely emarginate; staminal corona lobes terete, 3.5–4 mm long, 0.3–0.4 mm in diam., lower part yellow, connivent-erect, purple with white apex. Pollinaria: pollinium broadly ovoid, yellow, 0.31–0.33 × 0.21–0.22 mm, translators stout, hyaline, ca. 0.08 × 0.06 mm, corpusculum spathulate, reddish brown, 0.23–0.25 × 0.09–0.1 mm. Ovaries 2, ovoid, ca. 2 mm long, 0.5 mm in diam., glabrous. Follicles usually 2, linear-lanceolate in outline, green when young, turning reddish brown with age, 12–13 cm long, 2.5–3 mm in diam. Seeds ovate-oblong, 5–6 × 1.9–2 mm, coma 1–1.2 cm long, silky white.

Distribution:— Thailand (Tak Province).

Habitat & Ecology: —In sandy, calcareous soil in the open areas of limestone mountain at about 700 m elevation. Its known habitat is currently degraded due to human activities and soil erosion caused by heavy rains falling on cleared forest lands. The run-off carries soil into the local creeks and rivers ( Fig. 3 ). Flowering July–October.

Etymology:— This species is named in honor of Dr. Pramote Triboun, botanist of the Thailand Institute of Scientific and Technological Research, Bangkok, who first discovered and drew my attention to Ceropegia tribounii .

Discussion:— Ceropegia tribounii is a grass-like perennial herb that produces an erect stem arising from a subglobose tuber and one-flowered inflorescences. To the author’s knowledge, only few Thai Ceropegia species have such diagnostic characters, i.e. C. acicularis Kidyoo (2014a: 91) , C. suddeei Kidyoo (2014b: 569) , C. tenuicaulis Kidyoo (2014a: 93) and C. thailandica Meve (2009: 161) . The newly discovered species, C. tribounii clearly differs from all these species in both vegetative and reproductive morphology ( Fig. 2 ). While the others produce pedunculate inflorescences that are terminated by the single flower, and linear corolla lobes that are not connate at the tips, C. tribounii and C. acicularis have sessile inflorescences and obovate corolla lobes that are connate at the tips. Despite some common features, the last two species can be immediately distinguished at first sight from each other by their stems, leaves, and particularly size of flowers. Ceropegia tribounii produces an unbranched stem and linear-lanceolate leaves, whereas C. acicularis has a branched stem with aciculate leaves. The flowers of C. tribounii are much larger (tube 20–23 mm long, 6–8 mm in diam., lobes 17–19 × 7–8 mm) than those of C. acicularis (tube 6.5–9.3 mm long, 4.5–5.5 mm in diam., lobes 4.5–7.3 × 1.8–2.1 mm; Kidyoo 2014a) (see Fig. 2b and 2c ) that are, in addition, the smallest of this grass-like group.

Several field expeditions conducted in all regions of Thailand revealed that, while the other grass-like Thai species of Ceropegia grow in sandy soil in the open areas of a sandstone mountain at about 200 m elevation, C. tribounii grows in sandy-calcareous soil in the open areas of a limestone mountain at about 700 m elevation. Moreover, C. tribounii only occurs in the mountains near Thi Mo Bo waterfall in western Thailand, about 600 km far from the other members of the group that are widely distributed in the northeastern and eastern areas ( Kidyoo 2014a, b).

As Ceropegia tribounii is quite distinct morphologically from already-described species in Thailand, it is also compared below with C. anjanerica , an Indian species also exhibiting an erect habit, as well as similar floral traits. Despite its broader leaves, C. anjanerica is known to be related to narrow-leaved species ( Surveswaran et al. 2009). Both C. anjanerica and C. tribounii are perennial herbs with short, non-twining stems arising from a subglobose tuber. They produce one-flowered inflorescences and corolla tubes with only slightly inflated bases. Ceropegia tribounii , however, can be easily discerned by its sessile, linear-lanceolate leaves and broadly obovate corolla lobes that are shorter than the corolla tube and giving the “cage” a rather cubic outline. The interstaminal corona lobes are shortly pilose inside but otherwise glabrous and hardly bifid with an obtuse apex at each end. In comparison, C. anjanerica has elliptic to narrowly elliptic leaves with petioles of 0.2–0.5 cm in length, and much narrower obovate corolla lobes that are as long as the corolla tube and giving the “cage” an elongated ovate outline. Moreover, the interstaminal corona lobes are pilose only along the margin and bifid with an acute apex at each end.

IUCN Red List category:— Ceropegia tribounii is endemic to Thailand. The species is apparently rare and known from only one population of less than 20 mature individuals growing in degraded habitat. Following the IUCN Red List Categories and Criteria (2001), it is strongly suggested that C. tribounii should be treated as a critically endangered species (CR).

Additional specimens examined (paratypes): Ceropegia tribounii :— THAILAND. Tak: Tha Song Yang district, the mountains near Thi Mo Bo waterfall, 700 m elevation, 23 October 2012, M. Kidyoo 1574 (BCU!).

Figures

FIGURE 1. Illustrations of Ceropegia tribounii Kidyoo (a) habit, (b) flower, (c) top view of gynostegium, (d) side view of gynostegium, (e) calyx (f) pollinarium, (g) fruit, (h) seed. Drawn by Manit Kidyoo from M. Kidyoo 1608 (a–f) and M. Kidyoo 1574 (f–g).

FIGURE 2. Comparison of vegetative and reproductive parts between Ceropegia tribounii Kidyoo (a–b, a. habit, b. flower), C. acicularis (c. flowering branch), C. suddeei (d. flowering branch), C. tenuicaulis (e. flowering branch), and C. thailandica (f. flowering branch). Photo by Manit Kidyoo.

FIGURE 3. Photographs of natural habitat of Ceropegia tribounii Kidyoo, taken at different times: (a) habitat in July 2011, (b–c) habitat showing heavy soil erosion in October 2014. Photo by Manit Kidyoo.