Dregea taynguyenensis T.B. Tran & Rodda, 2018

Dregea taynguyenensis T.B. Tran & Rodda View in CoL , spec. nov. ( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Dregea taynguyenensis is most similar to D. cuneifolia due to the elliptic-oblong leaf blades, cuneate at base and acuminate at apex. The former is distinguished from the latter by having 7–10 secondary veins each side of midrib (vs. 5–6 in D. cuneifolia ), calyx lobes lanceolate to linear (vs. ovate) and corolla lobes 10.2–12.6 × 5.3–6.4 mm (vs. c. 4 × 4 mm).

Type:— Vietnam. Tay Nguyen: Gia Lai province, Kon Ka Kinh National Park , 14.26’00.1” N 108.21 ’45.7” E, 1194 m, 9 June 2011, T. B. Tran, V. H. Do & H. Q. Bui Bach0906201101 (holotype HN [ HN0000070158 ]; isotype HN [ HN0000070159 ]) .

Woody vine; main stem to 10 m long or more. Young stem pubescent, becoming glabrescent with age; internodes 7.5–10 cm long. Petioles 1.2–1.8 cm long, 2.5–3 mm in diam., pubescent; leaf blades elliptic or oblong, 10.8–12 × 3.6–3.8 cm, cuneate at base, acuminate at apex, glabrous above, pubescent below; secondary veins 7–10 on each side of midrib, tertiary venation reticulate, prominent below. Inflorescences axillary, pseudo-umbelliform, convex, 18–40-flowered; peduncle 4.1–7 cm long, pubescent. Flower bud conical, 8.2–8.3 × 9–10 mm just before anthesis, greenish white. Pedicels 2.7–3 cm long, 0.8–1.5 mm thick, pubescent. Flowers 27–29 mm in diam. Calyx lobes slightly overlapping to the right or to the left at base, lanceolate to linear, 2.4–5 × 0.7–1.5 mm, green flushed brown outside, green inside, pubescent outside, glabrous inside, margin ciliate; with one basal colleter at each sinus, colleters c. 0.2 × 0.2 mm. Corolla rotate to shallowly bowl-shaped, deeply divided; tube 3.6–5.9 mm long, glabrous outside; lobes 5, contorted to the right, triangular, 10.2–12.6 × 5.3–6.4 mm, greenish white outside, whitish green or yellowish flushed purple inside, ciliate. Corona staminal 5.5–7 mm in diam., 3.3–3.4 mm tall, slightly stipitate; stipe 1.16–1.66 mm tall; corona lobes fleshy, adnate to stamens, ovoid to sub-globose, slightly flattened above, 1.66–1.79 × 1.39–1.79 mm, white to cream, outer process obtuse, inner process narrowing to an acute tooth incumbent to anthers. Anthers with membranous apical appendages. Pollinia erect, oblong, oblanceolate to clavate, 0.58–0.76 × 0.12–0.21 mm, without pellucid margin; corpusculum rectangular, 0.24–0.28 × 0.16–0.19 mm; caudicle 0.19–0.21 × 0.04–0.05 mm. Ovary conical, c. 0.7 × c. 0.33 mm, glabrous. Fruit and seeds not seen.

Etymology:— The specific epithet refers to the type locality, Tay Nguyen area in Vietnam..

Distribution and ecology: — Dregea taynguyenensis is only found in Vietnam, Gia Lai province, Tay Nguyen area where it grows in sunny places in secondary forest, in association with Bidens pilosa Linnaeus (1753: 832) , Jasminum lanceolarium Roxburg (1820: 97) , Maclurodendron oligophlebium (Merrill 1923: 246) T.G. Hartley (1982: 13) , Mallotus paniculatus (Lamarck in Lamarck & Poiret 1786: 207) Müller Argoviensis (1865: 34), Melicope pteleifolia (Champion ex Bentham in Bentham 1851: 330) T.G. Hartley (1993: 521).

Phenology: –Flowering specimens were collected in June.

Conservation status:— Data Deficient ( DD; IUCN 2017 ). Dregea taynguyenensis is known only from the type locality and from two nearby locations all within Kon Ka Kinh National Park . A comprehensive botanical survey of the park has not been carried out to date. Even if we estimate the AOO as the entire Kon Ka Kinh National Park ( AOO <500 km 2), a provisional conservation status cannot be assessed, as we have no information on the number of population, their potential decline or fluctuation .

Observations: —The five species of Dregea found in Vietnam and neighbouring countries are clearly distinguishable from each other based on morphological characters ( Table 1). In sterile state D. taynguyenensis can only be confused with D. cuneifolia because both taxa have elliptic-oblong leaf blades, cuneate at base and acuminate at apex; while D. sinensis , D. volubilis and D. yunnanensis have ovate-cordate to suborbicular leaf blades (lanceolate in D. volubilis var. angustifolia J.D. Hooker (1883: 47) . The flowers of D. taynguyenensis are characterized by deeply divided corollas and lobes 10.2–12.6 × 5.3–6.4 mm, which are larger than those of the other three species. The species with the second largest corolla lobes is D. volubilis , (6–8 × 5–6 mm). Lastly, the calyx lobes of D. taynguyenensis are comparable in size with those of D. volubilis , however D. taynguyenensis has lanceolate to linear calyx lobes, while D. volubilis has ovate to oblong calyx lobes.