Hoya uncinata Teijsm. & Binn., Tijdschr. Nederl. Ind.

Rodda, Michele & Rahayu, Sri, 2018, A revision of the Hoya uncinata complex (Apocynaceae, Asclepiadoideae), with description of a new species, Phytotaxa 383 (3), pp. 252-258 : 253-256

Hoya uncinata Teijsm. & Binn., Tijdschr. Nederl. Ind. 25: 408 (1863) ( Fig. 1 )

Type:— Indonesia, Java and Sumatra “In silvis Javae et Sumatrae ins. prov. Palembang’ (not traced) ; ibid., auf Bäumen bei Padang, 900 m, 20 Jan. 1907, R. Schlechter 15916 (neotype, B [ B100277224 ] here designated) .

Hoya padangensis Schltr., Beih. Bot. Centralbl. 34(2): 15 (1916) syn. nov.

Type:— Indonesia, Sumatra, auf Bäumen bei Padang, 900 m, 20 Jan. 1907, R. Schlechter 15916 (lectotype, B [ B 100277224] here designated).

Delicate epiphytic climber with clear latex in all vegetative parts; all vegetative parts glabrous. Leafy stems cylindrical, slender, up to 4 mm in diam., dark brown or grey, with membranaceous peeling bark; internodes 5–15 cm long. Petioles terete, fleshy, 5–10 × 2–3 mm in diam.; lamina elliptic-lanceolate, fleshy, 7–10 × 1.5–3 cm, apex acute-acuminate, base rounded or cuneate, dark green above with numerous grey spots, lighter green underneath, venation pinnate, very faintly visible above, not visible beneath. Inflorescences sciadioidal, ca. 4 cm in diam., 8–22 flowered; peduncles extra-axillary, negatively geotropic or horizontal, terete, 1.5–5 cm × 2–3 mm in diam., glabrous; pedicels upright, 10–15 mm × 0.5–0.8 mm in diam., purplish-green, glabrous. Calyx lobes ovate, slightly spatulate, red or pink 1.8–2.5 × 0.7–1.3 mm, apex obtuse or round, glabrous; basal colleter 1 in each sepal sinus, triangular, 0.2–0.3 mm long. Flower buds globular, truncate at top, with 5 distinct lateral ridges, c. 6 mm in diam. before anthesis. Corolla rotate, deeply lobed, 1.5–1.7 cm in diam. when flattened, white tinged pink, thinly and minutely pubescent inside, outside glabrous, tube 2–3 mm long, 3–4 mm in diam., lobes laterally recurved, ovate with a triangular acute apex, slightly ascending, 6–7(–9) × 4.4–5.5 mm. Gynostegium stalked, stalk 0.5–0.8 mm tall, 1.5–1.8 mm in diam. (base); Corona staminal, 3–4 mm tall, 5.5–7 mm in diam., fleshy; corona lobes ovate, laterally compressed and slightly convex above, with revolute margins beneath, 3–4 × 1–1.5 mm, 3–4 mm tall, inner process erecto-patent with an acute tip c. 1 mm long, as long or slightly longer than the anthers, light pink, outer process ending in an incurved membranaceous appendage c. 0.5 mm, sometimes much reduced, white or light yellow. Anthers ovate, 0.8–0.85 × 0.45–0.5 mm, with apical round membranaceous appendage as long as the style-head apex. Pollinia oblong, with round apex and base and evident pellucid margin, 600–650 × 150–180 μm; caudicles attached at the base of the corpusculum, winged, corpusculum 600–650 × 250–300 μm; style-head 5 angled in cross section, with 5 spreading lobes alternating with the stamens, style-head convex, stipitate, as tall as the anther appendages, c. 0.8 × 0.6 mm. Ovary linear, 2–2.5 mm long, ca. 0.5–0.7 mm wide at the base. Immature fruits linear, c. 12 cm long, c. 5 mm diam., brownish-violet; seed not seen.

Notes: — Hoya uncinata was described based on materials collected from Java and Sumatra. Its flowers were originally described as being negatively geotropic (i.e., ‘ flores erecti ’), a rare occurrence in Hoya . Peduncles in Hoya are commonly positively geotropic, less frequently neither positively or negatively geotropic “laterally held” and very rarely negatively geotropic ( Lamb & Rodda 2016). Within each inflorescence the orientation of flowers depends on the inflorescence type. In globose inflorescences individual flowers range from positively to negatively geotropic, while in flat or concave/convex inflorescences all flowers are either positively or negatively geotropic. Species with both peduncles and individual flowers negatively geotropic are for example Hoya mitrata Kerr (1940 : t. 3406) and Hoya oreostemma Schlechter (1913: 126) . Hoya uncinata has negatively geotropic peduncles (sometimes laterally held) and individual flowers that range from negatively geotropic to horizontal (rarely some flowers are positively geotropic in very rich inflorescences). Hoya uncinata was observed alive by Teijsmann and Binnendijk as they noted the tropism of the flowers, impossible to study on herbarium materials, as well as leaves and flowers colours. Apart from the erect flowers the species is characterised by laterally compressed corona lobes, convex above and bearing an apiculate, hooked and inflexed outer process that however is sometimes much reduced. Hoya padangensis Schltr. , also described from Sumatra, bears this set of characters and is here treated as a new synonym of Hoya uncinata .

At BO only one original specimen of Hoya apiculata Scheffer (1876: 37) (= Hoya australis Traill [1830: 28] ) was found, which is a Teijsmann collection ( Forster & Liddle, 1994). Numerous original specimens of Hoya species described by Teijsmann and Binnendijk have been located at L and U. After an accurate examination of all Hoya materials at BO, L and U we were unable to trace any original material of Hoya uncinata . It is possible that the original material of H. uncinata was lost or that the taxon description was based on live plants only. We therefore designate R. Schlechter 15916 ( B) as neotype for H. uncinata . The same specimen is here designated as lectotype for Hoya padangensis , in accordance with Art 9.1 & 9.3 of the ICN ( Turland et al. 2018). Therefore, the two names are homotypic synonyms.

Distribution and ecology: — Indonesia, Java and Sumatra. Records of Hoya uncinata are few and based mostly on old and / or unlocalised materials. It was described from materials collected in Java and Sumatra, without specific location and elevation. According to the herbarium records Hoya uncinata collected at Gunung Pantjar, Bogor, West Java, was growing close to warm spring water, at 500 m altitude and a specimen collected at Padang Panjang, West Sumatra, was growing at 900 m.

Conservation status: — A rarely collected species from Java and Sumatra. The most recently collected specimen was collected in 1963 in Java is Nengah Wirawan 128 ( SING) ; however, because of the heavily damaged flowers it is impossible to confirm its identity. The earlier record for the island is Backer 9040 ( BO), collected in 1913. In Sumatra no collections have been made since Schlechter’s type specimen Schlechter 15916 ( B). Without any information on population size and decline, the preliminary conservation assessment for Hoya uncinata is Data Deficient ( DD, IUCN 2017 )

Figures

FIGURE 1. Comparison between the species in the Hoya uncinata complex. A, Hoya corneri. Based on M. Rodda MR647 (SING); B, Hoya uncinata, based on Rodda M MR609 (SING); C. Hoya ruthiae, based on M. Rodda MR606 (SING). Photos by M. Rodda.