Vincetoxicum strigosum A. Kidyoo, 2020

Kidyoo, Aroonrat, 2020, Vincetoxicum strigosum (Asclepiadoideae, Apocynaceae), a new species from northeastern Thailand, Phytotaxa 438 (4), pp. 237-246 : 238-245

publication ID

https://doi.org/ 10.11646/phytotaxa.438.4.2

persistent identifier

https://treatment.plazi.org/id/03DE87C6-FFAD-1C1D-2582-FAB68AE8FF5B

treatment provided by

Felipe

scientific name

Vincetoxicum strigosum A. Kidyoo
status

sp. nov.

Vincetoxicum strigosum A. Kidyoo View in CoL sp. nov. ( Figs. 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 )

Type:— THAILAND. Nong Bua Lamphu province: Wat Phuttha Banphot, 350 m elevation, 8 November 2018, A. Kidyoo 51 (holotype BCU!).

Diagnosis:— Vincetoxicum strigosum sp. nov. is related to V. kerrii , being similar in having slender twinning stem and branches, narrowly lanceolate-oblong leaves, and branched inflorescence, but is clearly distinguished by its strigose adaxial leaf surface, short, stout peduncle and rachis, compact inflorescence, lanceolate calyx lobes that are longer than corolla tube, stipitate gynostegium, corona lobes with rounded apex, and obovate corpusculum. On the contrary, V. kerrii has glabrous leaves with sparse hairs only on the midrib on both surfaces, long, slender peduncle and rachis, lax inflorescence, triangular-ovate calyx lobes that are as long as corolla tube, sessile gynostegium, corona lobes with truncate apex, and oblong-shaped corpusculum.

Slender climber, 1–3 m long with clear exudate in all vegetative parts. Stems and branches twining, terete; internodes 5–25 cm long, 0.7–1.2 mm in diameter, green to greyish green, glabrous to sparsely strigose. Leaves opposite; petiole terete, slightly canaliculate and pubescent along the upper side, 3.0–5.0 mm long, 0.6–0.8 mm in diameter; blade membranous, ovate-oblong to oblong-lanceolate, 3.3–7.0 × 0.4–1.0 cm; leaf margins ciliate; leaf base obtuse to rounded, bearing 1–2 ovate-lanceolate glands on the adaxial surface, leaf apex acute to acuminate; adaxial surface green to dark green, strigose, with cuticle accumulation on the outer periclinal wall of epidermal cells taking the form of an interlace pattern comprising rings of ten or more elongated elements arranged around a circular area and joining one another, abaxial surface paler, glabrous or sparsely hairy on veins; midrib prominent on lower surface, sparsely hairy, lateral veins visible, 9–14 on each side, at acute angle to the midrib. Inflorescence 1-3 times branched with condensed rachis, extra-axillary, 10–15-flowered; peduncle stout, 1–3 mm long, 0.8–1.1 mm in diameter, green, greenish brown to reddish brown, glabrous to sparsely pubescent; pedicels yellowish green to yellow, 7–10 mm long, 0.6–0.7 mm in diameter, glabrous to sparsely pubescent; bracts minute, attached at the base of the pedicel, triangular-lanceolate, green to greenish brown, sparsely pubescent, acute at apex. Flower bud broadly pyramidal. Calyx lobes lanceolate, 1.4–1.5 × 0.5–0.6 mm, yellowish green, sparsely pubescent, acute to acuminate at apex, bearing an ovate-oblong gland inside each lobe sinus. Corolla rotate, 7–9 mm in diameter, greenish yellow to yellowish orange, sometimes adaxially tinged pale dull reddish purple at the lower mid-portion of lobes continuing down mouth of tube; tube 0.9–1.2 mm long, adaxial surface puberulent, abaxial surface glabrous; lobes twisted in bud, spreading at anthesis, ovate, 3–3.4 × 2.4–2.8 mm, margins recurved, acute at apex, slightly curved. Gynostegium 1.6–1.8 mm in diameter, 1.3–1.5 mm in length, subsessile, stipe ca. 0.2 mm in length. Staminal corona lobes 5, inserted at the base of the stamens, fleshy, ovoid, half as long as anther, 0.5–0.6 × 0.6–0.7 mm, yellow, often with conspicuous purple centre, apex rounded. Anthers reniform, orange with white membranous appendage, attached around style-head. Pollinaria, 5, pendulous, almost horizontally disposed with respect to the filament, attached to the translator arms by their outer end; pollinia ovoid, yellow, 0.15–0.16 × 0.11–0.12 mm; translator arms hyaline, 0.04–0.05 mm long; corpusculum ovate, reddish brown, 0.07–0.08 × 0.05–0.06 mm. Carpels ovoid, glabrous, 1.1–1.2 mm long, ca 0.5 mm in diameter; style-head truncate, pentagonal. Fruit not seen.

Distribution and habitat:— Vincetoxicum strigosum is known from Nong Bua Lamphu and Loei provinces, Thailand. This twining herb grows in bamboo forests at the elevation of 350–500 m ( Fig. 5 View FIGURE 5 ).

Phenology:—Flowering from November to January.

Etymology:—The specific epithet ‘ strigosum ’ refers to the leaves’ strigose adaxial surface.

Conservation status:— Vincetoxicum strigosum is only known from two closely located sites (ca. 100 km from each other) in northeastern Thailand, with one of the collections from 2008 and the other from an outside protected area prone to the effects of disruptive human activities. At present, the number of mature plants in each locality is unknown. Following IUCN (2019), a provisional conservation assessment of Endangered: B1ab(iii) is assigned due to its extent of occurrence of much smaller than 5,000 km 2, restricted geographic distribution, small number of locations that are susceptible to threats within a short time period.

Discussion:— Vincetoxicum strigosum possesses vegetative and floral morphology that mostly correspond to those of the former Tylophora ( Liede 1996; Liede-Schumann et al. 2012). The new species is recognized by a twining habit, clear latex, petiolate narrowly lanceolate-oblong, membranous leaves with obtuse-rounded base and acute-acuminate apex, pedunculate branched inflorescences, adaxially puberulent corolla lobes, and fleshy staminal corona lobes. Besides V. strigosum , the other member of Vincetoxicum to have such a combination of characteristics is V. kerrii , a species also found in Thailand ( Thaithong et al. 2018). However, V. strigosum is clearly distinct by its strigose adaxial leaf surface, and shorter stout peduncle and rachis, resulting in a compact inflorescence, while V. kerrii has both leaf surfaces glabrous with sparse trichomes only on the midrib, and conspicuously longer, slender peduncle and rachis, producing lax inflorescence. Vincetoxicum strigosum further differs from V. kerrii in its lanceolate calyx lobes that are longer than corolla tube, gynostegium with apparent stipe, and corona scales with rounded apex, the latter species, on the other hand, has triangular-ovate calyx lobes being as long as corolla tube, sessile gynostegium, and corona scales with truncate apex ( Table 1). Furthermore, preliminary observations of reproductive phenology in the field revealed diurnal anthesis in V. strigosum , but nocturnal anthesis in V. kerrii , the flowers of which opened in the late evening or at night and closed during the day. This finding most likely suggests that these two species rely on different pollinators for their sexual reproduction ( Faegri & van der Pijl 1979; Lumer & Yost 1995; Maclvor et al. 2017)

Additional specimen examined:— Vincetoxicum strigosum A. Kidyoo (paratype): THAILAND. Loei Province: Phu Kradueng National Park, ca. 500 m elevation, 10 January 2008, S. Wongpakum s.n. (BCU!).

Vincetoxicum kerrii (Craib) A. Kidyoo : THAILAND. Chiang Mai province: Doi sootep, 1,350 m elevation, 27 June 1909, Kerr 704 (K!); Ban Khun Chang Khian , 1,400 m elevation, 20 July 2019, A. Kidyoo 65 ( BCU!) .

and the similar species V. kerrii (Craib) A. Kidyoo

BCU

Chulalongkorn University

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