Hoya tamdaoensis Rodda & T.B.Tran, 2015

Rodda, Michele, Tr ần, Th ế Bách & Nguy ễn, Qu ốc Bình, 2015, Hoya tamdaoensis (Apocynaceae, Asclepiadoideae), a new species from Vietnam, Phytotaxa 217 (3), pp. 288-292 : 288-291

Hoya tamdaoensis Rodda & T.B.Tran spec. nov. ( Figs. 1 & 2 )

Similar to Hoya siamica Craib (1910: 419) in exhibiting inflorescences positively geotropic, convex, flowers numerous, corollas white, pubescent within, and leaves glabrous, but distinguished by the corolla size (1.8–2.2 cm diam. vs. <1 cm diam. in H. siamica ) and the lamina shape (base attenuate-rounded and apex caudate vs. base cuneate or acute and apex acute or acuminate in H. siamica ).

TYPE:— VIETNAM, Vĩnh Phúc prov., Tam Đ ảo N. P., Máy Gi ấy trail, 1072 m, 20 September 2011, Nguyễn Qu ốc Bình, Jana Leong- Škorničková, Trần Hữu Đăng VNM-B1465 (holotype, SING!; isotypes HN!, VNMN!) .

Lithophytic climber with white exudate in all vegetative parts, glabrous, except young stems sparsely pubescent with retrorse hairs. Stems slender, internodes (5–)8–12(–15) cm × 1.5–3 mm, dark green to brownish purple; adventitious root sparsely produced along the stem. Leaves wine-red when young; petiole recurved, held at an almost right angle to the lamina, 0.8–2 cm × 1.5–2.5 mm, dark green to brownish purple; lamina oblong-lanceolate, (4–)5–10 × (1.5–) 2–3 cm, base attenuate-rounded, apex caudate, margin entire, reflexed in older leaves; venation pinnate, secondary veins in 4–7 pairs, borne at 70 o –90 o to midrib, anastomosing, tertiary venation reticulate, dark green above, glossy with occasional grey spots, midrib depressed above, raised underneath, lighter green with a slightly darker midrib and edge underneath; colleters one at each lamina base, triangular, 0.8–1 × 0.8–1 mm. Inflorescence pseudo-umbellate, convex; peduncle 3–10 cm × 1.8–2.5 mm diam., dark green to purplish brown, glabrous. Flowers (4–)10–15 per inflorescence; pedicel 2–2.5 cm × 0.8–1.2 mm diam., light green, glabrous. Calyx lobes broadly triangular, 1.5–2 × 1–1.5 mm wide, light green with purple spots, glabrous; basal colleter one per calyx lobe sinus, ovate to triangular, 1.5–2 × 1–1.2 mm, apex rounded. Corolla rotate, flat, 1.8–2.2 cm diam., tube 5–6 mm long, thickly pubescent inside, glabrous outside, lobes broadly triangular, 6–8 × 5.5–7 mm, white, margin recurved, apex acute, revolute, thickly pubescent inside with glabrous apex, glabrous outside. Corona staminal, 9–10 mm diam., 4–5 mm high, lobes ovate, 3.5–4.5 × 2.3–2.6 mm, concave above, underneath sulcate with inrolled margins, outer process apex rounded, inner process acuminate. Anthers ovate, ca. 1.3 × 1.2 mm, with apical round membranaceous appendage exceeding the style-head by 0.5–0.7 mm. Pollinia clavate, 650–750 × 270–320 μm, narrowing towards the base, apex truncate, sterile edge all along the outer edge of the pollinium; corpusculum rhomboid, 300–400 × 180–220 μm, apex acute; caudicle broad, spathulate, hyaline, ca. 150 × 100 μm at the widest. Style-head 5-angled in cross section, with 5 lobes alternating with the stamens, style-head apex round, ca. 1 mm long, 2–2.5 mm broad at the base. Ovaries 2, ovate, 1.5–2 mm × ca. 1 mm wide at the base, light green, apex narrow. Fruit and seed not seen.

Etymology: —The new species is named after the collection locality, Tam Đảo National Park, Vietnam.

Distribution and ecology: —Only known from the type locality in Tam Đảo National Park, Vietnam. Hoya tamdaoensis was found growing epilithically on limestone covered by moss in evergreen lower montane forest.

Conservation status: —Known from only one locality; the preliminary conservation status of Hoya tamdaoensis is Data Deficient (DD; IUCN 2014).

Notes: — Hoya tamdaoensis is morphologically similar to the Hoya siamica species complex that has been well documented in Thailand ( Tungmunnithum et al. 2011). The complex is very variable in vegetative and reproductive morphology and is likely to include more than one taxon. Both H. tamdaoensis and members of the H. siamica complex exhibit inflorescences positively geotropic, corollas rotate, pubescent within, and corona lobes ovate. The leaves of H. siamica are very variable, ovate, obovate, elliptic, lanceolate, and oblanceolate.

Hoya tamdaoensis can be distinguished from H. siamica by corolla size (1.8–2.2 cm diam. vs. <1 cm diam. in H. siamica ) and the lamina shape (base attenuate-rounded and apex caudate vs. base cuneate or acute and apex acute or acuminate in H. siamica ). The abaxial laminar surface of H. tamdaoensis is light green with a slightly darker midrib and edge, while in H. siamica it is uniformly coloured. Young leaves of H. tamdaoensis are dark wine-red in colour, while the young leaves of H. siamica are pale green. Lastly, the petioles of H. tamdaoensis form an acute to often almost right angle with the lamina, while in H. siamica the petiole and lamina form an almost 180 o angle.

Additional specimens examined:—UNLOCALISED. (nursery purchase), 27 Aug 2014, M. Rodda MR729, collected from material cultivated at the Singapore Botanic Gardens (SING!).

Figures

FIGURE 2. Photographs of flower details of Hoya tamdaoensis cultivated at the Singapore Botanic Gardens (M. Rodda MR729, SING): a. Three single flowers with evident corolla and corona; b. Corolla, abaxial view; c. Corona, top view; d. Corona, underneath; e. Corona, side view; f. Flower, longitudinal section; g. Calyx and ovaries, side view; h. Calyx and ovaries, top view; i. Immature peduncle borne on a young pubescent branch; j. Pollinarium. Photographs by M. Rodda.

FIGURE. 1. Photographs of a living plant of Hoya tamdaoensis cultivated at the Singapore Botanic Gardens (M. Rodda MR729, SING) a. Inflorescence, adaxial view; b. Inflorescence, abaxial view; c. Branch, peduncle, and pendulous inflorescence; d. Leaves, four leaves from mature to immature (left to right), each leaf adaxial (right) and abaxial (left); e. Leaves, side view, with evident attachment of the petiole to the lamina at almost right angle. Photographs by M. Rodda.