Hoya ruthiae Rodda, 2015

Rodda, Michele, 2015, Two new species of Hoya R. Br. (Apocynaceae, Asclepiadoideae) from Borneo, PhytoKeys 53, pp. 83-93 : 84

Hoya ruthiae Rodda sp. nov. Figs 1 , 2

Diagnostic characters.

Similar to Hoya uncinata Teijsm. and Binn as both species have clear exudate, deeply lobed rotate corolla and corpusculum of the pollinarium almost as large as the pollinium. The flattened corolla is smaller (1.5-1.7 cm in diameter) with ovate lobes in Hoya uncinata , while the corolla of Hoya ruthiae is 1.8-2.2 cm in diameter with narrowly lanceolate lobes.

Type.

Malaysia, Sabah, Lahad Datu, Bukit Baturong, on limestone, 7 July 2000, Kiew R RK5029 (SING, holotype; barcode SING0077484).

Description.

Delicate lithophytic climber with clear exudate in all vegetative parts; all vegetative parts glabrous. Leafy stems cylindrical, slender, up to 4 mm in diameter, dark brown or grey, with membranaceous peeling bark; internodes 5-15 cm long. Petioles terete, fleshy, 5-15 × 1.5-3 mm in diameter, lamina lanceolate, fleshy, (5-)7-15 × 1.5-3 cm, apex acute-acuminate, base cuneate, light green above turning red in bright light with numerous grey spots, lighter green underneath; penninerved, secondary veins obscure. Inflorescences pseudo-umbelliform or globular, 3-4 cm in diameter, 4-20 flowered; peduncles persistent, extra-axillary, terete, 1-3 cm × 1.5-2.5 mm in diameter, glabrous; pedicels 10-15 mm × 0.5-0.8 mm in diameter, glabrous. Buds conical with a 5-ridged base, ca. 10 × 6 mm. Calyx lobes triangular, white-pink 1.3-1.5 × 0.7-1 mm, apex rounded, glabrous; basal colleters 1 in each sepal sinus, ovoid. Corolla rotate, deeply lobed, 1-1.5 cm in diameter, 1.8-2.2 cm when flattened, white tinged pink, thinly and minutely pubescent inside, outside glabrous, tube 1.5-2 mm long; corolla lobes narrowly lanceolate with a triangular acuminate apex, 9-10 × 3-4 mm, laterally revolute, lobe tips recurved. Gynostegium stalked, corona column conical 1-1.2 × ca. 2 mm diam, glabrous; corona staminal, 2.5-3 mm high, 6-7 mm in diameter, fleshy, yellow with a purple centre; corona lobes laterally compressed, ovate above, with revolute margins beneath, 2.8-3.2 mm × 1-1.2 mm, inner process erecto-patent, linear with an acute tip, as high as the anthers, outer process round. Anthers ovate, 650-750 × 300-400 µm, with apical round membranaceous appendage as high as the style-head apex. Pollinia oblong, with obliquely truncate apex and round base and evident pellucid margin, 550-630 × 150-200 μm; caudicles attached at the base of the retinaculum, elongate, ca. 150 µm long, corpusculum 600-650 × 250-300 μm; style-head 5-angled in cross section, with 5 spreading lobes alternating with the stamens; style-head apex columnar, 1-1.2 mm long, ca. 0.5 mm broad at the base, apex conical; ovary linear, ca. 2 mm long, each carpel ca. 0.5 mm wide at the base. Fruits and seeds unknown.

Etymology.

This species is named after Ruth Kiew (1946-), tropical botanist based at the Forest Research Institute Malaysia and author of numerous publications on Begonia L. and Gesneriaceae , among others.

Distribution and ecology.

Hoya ruthiae is only known from Bukit Baturong, Sabah, Malaysia, where it was found growing on limestone.

Conservation status.

The distribution area, population size and possible threats to the habitat of Hoya ruthiae are not known, as it is only known from the type specimen and unlocalised cultivated material. It is therefore considered Data Deficient (DD) ( IUCN 2014).

Notes.

The most striking feature of Hoya ruthiae is its lack of coloured latex. Other species lacking coloured latex are the type species of the genus Hoya carnosa R.Br. and several morphologically similar taxa ( Rodda and Simonsson Juhonewe 2012). All these have rotate corollas with thickly pubescent lobes within and rhomboid corona lobes with narrow inner and outer corona lobe processes. In Borneo only Hoya monetteae T. Green belongs to this group. Hoya ruthiae , as mentioned above, is morphologically very similar to Hoya uncinata , another non-laticiferous species known to occur in Java and Sumatra. Both species have deeply lobed rotate corollas, laterally compressed corona lobes and corpusculum of the pollinarium almost as large as the pollinium. Hoya ruthiae has larger flowers (1.8-2.2 cm in diameter when flattened vs. 1.5-1.7 cm) and the corolla lobes are narrowly lanceolate (vs. ovate in Hoya uncinata ). The corona lobes of both species are ovate but in Hoya ruthiae the outer process is round while in Hoya uncinata it terminates in an incurved membranaceous apiculate appendage. Flowers of Hoya uncinata are illustrated in Fig. 2 .

Additional specimens examined.

Unlocalised (nursery origin), Cultivated in Thailand, Ratchaburi Prov., Ratchaburi, 23 March 2014, Rodda M MR606 (SING).

Figures

Figure 1. Hoya ruthiae photographed from Rodda M. MR 606 (SING) prior to pressing A Flower, lateral view with two corolla lobes removed B Corolla, underneath C Corolla and corona, top view D Corona, underneath E Pedicel, calyx and ovaries F Pollinarium with twin pollinia. (Photographs by M. Rodda)

Figure 2. Hoya ruthiae photographed from Rodda M. MR 606 (SING) prior to pressing A Inflorescence D, E, F, G Two leaves (D, F adaxial surface E, G abaxial surface). Hoya uncinata photographed from Rodda M MR 607 (SING) prior to pressing B Flower, lateral view C Flower, top view. (Photographs by M. Rodda)