Hoya rigidifolia S.Rahayu & Rodda, 2019

Rahayu, Sri & Rodda, Michele, 2019, Hoya of Sumatra, an updated checklist, three new species, and a new subspecies, European Journal of Taxonomy 508, pp. 1-23 : 12-13

Hoya rigidifolia S.Rahayu & Rodda sp. nov.

urn:lsid:ipni.org:names:77195000-1 Figs 1 E–F, 2E–G

Etymology

The new species is named for its rigid and stiff leaves.

Type material

Holotype

INDONESIA • Sumatra, western Sumatra, Mentawai Islands, Pulau Siberut ; 100 m a.s.l.; Aug. 2014; S. Rahayu 865 leg.; vouchered from live collection at Bogor Botanic Garden on 26 Sep. 2016 as ‘ S. Hidayat B9710110’; BO.

Description

Epiphytic climber, with white latex in all vegetative parts. Roots adventitious below the nodes and along the internodes. Stems climbing, 3–4 mm in diameter, dull brown, sparsely pubescent; older stems grey, glabrous; internodes 4–10 cm. Leaf blades 4–12(15) × 2.5–5 cm, stiff and succulent, lanceolate to oblong, base acute, apex apiculate, mid to pale green on adaxial surface with sparse grey spots, pale green on abaxial surface with darker lines corresponding with the main vein and two prominent secondary veins, glabrous or sparsely pubescent when young, venation pinnate but with two prominent secondary veins running along the entire length of the lamina, and with a further 3–10 small secondary veins each side, primary and secondary veins depressed on adaxial surface, flat on abaxial surface; basal colleter ca 1 × 1.5 mm, one at each lamina base, broadly triangular, pale brown/cream; petioles 7–25 × 4–6 mm, terete, thicker than stems, pale brown, sparsely pubescent when young. Inflorescences 3.5–4 cm in diameter, of 20–25 flowers, sciadioidal, convex; peduncles 15–30 × ca 3 mm, terete, extraaxillary, laterally held, one at each node, producing flowers over an extended period of time, brownish, sparsely pubescent. Flowers with terete pedicels 13–17 × 0.7–1 mm, pale brownish yellow, minutely papillose. Calyx lobes ovate or round, apex rounded, 1–1.5 × 0.8–1 mm, minutely papillose outside, glabrous inside, ciliate; basal colleters 250–300 × 120–150 µm, ovoid, one at each calyx sinus. Corolla rotate, 10–12 mm in diameter when flattened; tube ca 1.5 mm long, cream inside, pale brown outside, glabrous; lobes 3.3–3.7 × 2.4–2.8 mm, ovate, valvate in bud, with incurved acute tip, cream fading to pale brown at the tip inside, brown outside, glabrous. Corona staminal, 1.2–1.4 mm high, 3.7–4.2 mm in diameter, white; lobes 2–2.3 × 1.1–1.2 mm, attached at the back of the anthers, held at a ca 80º angle, ovoid, slightly carinate above, inner process acute, erect, outer process rounded, spreading, with a basal revolute margin. Anthers ca 0.7 × 0.6 mm, ovate, including a thin apical round membranaceous appendage. Pollinia 350–400 × 130–150 μm, oblong, with a round base and an obliquely truncate apex; with a pellucid margin along the outer edge; caudicles ca 40 × 20 μm, much reduced; corpusculum 120–140 × ca 50 μm, oblong; style-head 5-angled in cross section, with five spreading lobes alternating with the stamens, style-head apex depressed with a central conical acute tip ca 200 µm high; ovary 0.8–0.9 mm high, ca 0.35 mm in diameter at the base, conical, lightly curved, apex acute. Fruit and seed not observed.

Distribution and habitat

Hoya rigidifolia sp. nov. is only known from the type locality in the lowland forest of Pulau Siberut, southern Sumatra, Indonesia.

Conservation status

Known only from a single collection and lacking information on the distribution area, the population size and the possible threats to the habitat, H. rigidifolia sp. nov. is considered as Data Deficient (DD) ( IUCN 2012).

Notes

Hoya rigidifolia sp. nov. flowers only open for a single day. The flowers of H. finlaysonii are also open for a single day and have a similar flower morphology (rotate corolla, ovoid corona lobes of similar size). Both species are, however, easily separated based on leaf characters. Hoya finlaysonii has lanceolate to oblong leaves with pinnate venation, usually darker than the rest of the lamina; H. rigidifolia sp. nov. also has pinnate venation, but additionally it has two basal secondary veins running along the entire length of the lamina. The leaf venation of H. erythrina Rintz (1978) is similar to that of H. rigidifolia sp. nov.; however, both species can be separated based on flower charaters: H. erythrina has flowers with corolla> 15 mm in diameter when flattened, long-pubescent inside, and lasting> 2 days, while H. rigidifolia sp. nov. has flowers with corolla <12 mm in diameter when flattened, glabrous inside, and lasting one day.

Figures

Fig. 1. Flowers. A, C, E. Top view of the flower. B, D, F. Side view of the flower, with part of corolla removed. A–B. H. danumensis subsp. amarii S.Rahayu & Rodda subsp. nov. (Amar Husein Sitompul s.n. leg., BO). C–D. H. solokensis S.Rahayu & Rodda sp. nov. (Fadly s.n. leg., BO). E–F. H. rigidifolia S.Rahayu & Rodda sp. nov. (S. Rahayu 865 leg., BO). Drawing: X. Y. Loh.