Hoya, Rodda, Michele & Ercole, Enrico, 2014

Rodda, Michele & Ercole, Enrico, 2014, --- Hoya- -- papaschonii- -- (Apocynaceae: Asclepiadoideae), a new species from southern Thailand with a peculiar corona, Phytotaxa 175 (2), pp. 97-106 : 101-104

Hoya ­­­ papaschonii ­­­ Rodda, spec. nov. ( Figs. 3 & 4 )

Similar in habit to Hoya multiflora , and in corolla morphology to Hoya telosmoides but the gynostegial corona presents a unique combination of both staminal and interstaminal lobes.

Type:— THAILAND. Original collection in Yala: Betong , cultivated in Thailand , Ratchaburi Province, Ratchaburi, November 2012, Papaschon Chamwomg KEW2012-011 (holotype BKF, isotypes BCU, K, SING) .

Epiphytic shrub, with white latex in all vegetative parts. Roots only basal, no adventitious roots observed. Stems slender, 2–4 mm diam., bright green, sparsely pubescent; older stems grey, glabrous; internodes (1.5) 4–8 cm. Leaf blades thin, not succulent, chartaceous when dry, lanceolate, base acute, apex acuminate, 7–12 × 2–4 cm, dark green on adaxial surface, lighter green on abaxial surface, glabrous, venation pinnate, midrib slightly depressed on adaxial surface, convex on abaxial surface, secondary veins 5–7 pairs, basal colleters absent; petioles terete channelled above, (5)10– 15(20) × (1.5) 2–3 mm in diam., green, sparsely pubescent. Inflorescences umbelliform, convex, of 4–10(15) flowers, peduncles extra-axillary, negatively geotropic or rarely horizontal, unbranched, 1 or rarely 2 at each node, producing flowers only once, terete, 2–25 mm × 1–1.5 mm, green, sparsely pubescent just below the rachis, otherwise glabrous; rachis with membranaceous bracts at the base of each pedicel, triangular, ca. 1 × 1 mm, glabrous. Flowers with terete pedicels 4–10 mm × ca. 1 mm in diam, light green, glabrous. Calyx lobes ovate- broadly triangular, apex round, 1.8–2.2 × 1–2 mm, light green, glabrous, basal colleters absent. Corolla tube basally bulbous, tightly enveloping the corona, with a contracted throat, a short almost straight tube and free, lanceolate, spreading lobes, white-cream coloured; basal bulbous part 1.8–2.2 mm tall, 3–4 mm diam., tube ca. 2.5 mm long, ca. 2 mm wide at the base, ca. 3 mm at the apex, free lobes triangular, valvate in bud, laterally recurved outward, 2.5–3.5 × 1.5–2 mm, tube sparsely pubescent inside, lobes glabrous. Corona gynostegial, stiff and waxy-looking with staminal (Cs) and interstaminal C (is) elements, 2–2.5 mm high, 3–4 mm in diam., ivory white; Cs inner lobes erect, recurved inward, oblong, alternating with the pollinaria, ca. 1.5 × 0.5 mm, Cs outer lobes missing; C (is) forming 5 globose lobes with an umbonate tip. Guide rail terminating in the umbo. Anthers broadly triangular, ca. 1 × 0.7 mm, with apical round membranaceous appendage just shorter than the style-head apex. Pollinia oblong, narrowing towards the base with a round base and apex, 380–420 × 80–110 μm; pellucid margin apical, short, limited to the upper outer half of the pollinium; caudicles much reduced, 60–70 µm long; retinaculum ovoid, 120–140 × 50–60 µm; style-head 5 angled in cross section, with 5 spreading lobes alternating with the stamens, style-head apex conical, 1–1.5 mm long, 0.8–1 mm broad at the base, apex acute; ovary bi-carpellate, ovoid, apex narrowed, truncate, 1.5–2 mm high. Fruits single or paired fusiform follicles, held at ca. 90° to each other when paired, 7–9 cm × 3–5 mm, light green when immature, light brown at maturity, glabrous. Seeds 15–30 in each follicle, slightly flattened, without differentiated margins, 4–5 × ca. 1 mm, long-comose, coma 3–4 cm long.

Etymology:— The new species is named after the collector and Hoya enthusiast Mr. Papaschon Chamwong who, in 2012, sent a specimen of the new species to Singapore Botanic Gardens for identification.

Distribution and ecology:— Hoya papaschonii is only known from two collections in Betong District, Yala Province in southern Thailand. It was collected in evergreen forest, where it was growing epiphytically.

Conservation status:— Known only from two collections from Yala Province in Thailand. The distribution area, the population size and the possible threats to the habitat are unknown. We therefore consider H. papaschonii as Data Deficient (DD) ( IUCN 2014).

Notes:— Hoya papaschonii exhibits a pellucid margin along the outer portion of the pollinium, a character typical of Hoya ( Wanntorp & Kunze 2009) .

Among species of Hoya , the tubular corolla with free spreading lobes of H. papaschonii , is only similar to that of H. telosmoides , a species from the highlands of Borneo. The two taxa are closely related and belong to Clade III ( Fig. 1 ). However, in H. telosmoides the base of the corolla is inflated and does not tightly envelop the corona, the corona is staminal and the corona lobes present the Hoya -typical inrolled anther skirt. Among genera closely related to Hoya , similar corollas are also encountered in Oreosparte celebica Schlechter (1916: 16) ( Rodda & Omlor 2014), in Dischidia and in unpublished taxa of Oreosparte and Hoya .

The general morphology of the corona of H. papaschonii is dissimilar from all known species belonging to the genus, but instead superficially resembles the corona of a group of species of Cynanchum formerly included in Sarcostemma ( Meve & Liede-Schumann 2012) , in which the corona exhibits 5 distinct erect staminal lobes and a continuous basal ring of staminal and interstaminal elements. However, in Cynanchum the guide rails are linear and terminate shortly below the pollinaria, while in H. papaschonii they are very long and terminate at the umbonate tip of the interstaminal lobe. A separation of guide rail and nectar tube as suggested by Kunze & Wanntorp (2008a) is not evident in H. papaschonii .

Additional specimens examined:— THAILAND. Yala, Betong, Hala-Bala , 22 June 1999, C . Niyomdham 5715 ( BKF!)

Figures

FIGURE 1. Best-known ML tree obtained from the combined nuclear ribosomal regions ITS and 5’-ETS and psbA-trnH and trnT-trnL intergenic spacers data set. The tree is rooted under the assumption that Dischidia and Hoya are mutually monophyletic. The part of the tree including clades V and VI, here contracted, is presented in Fig. 2. Bootstrap support values>60 (based on 100 replicates) are indicated at branches. Voucher information and GenBank accession numbers for H. papaschonii can be found in the Materials and Methods section. For voucher information and GenBank accession numbers of all other sequences see Wanntorp et al. (2014, electronic supplement S1). Species with a shrubby habit are marked by a round symbol; species with short-lived peduncles are marked by a square symbol. In the case names have been updated, the original name is indicated in brackets.

FIGURE 3. Hoya papaschonii: a. Whole plant; b. Flower, lateral view; c & d. Corona, lateral view; e. Corona, top view; f. Flower, longitudinal section; g. Pollinarium. Drawn by M. Rodda, based on Papaschon Chamwomg KEW2012-011 (SING)

FIGURE 4. Photographs of a living plant of Hoya papaschonii cultivated at the Singapore Botanic Gardens (acc. no. 20132440): a. Flowering branch and paired fruits; b. Bud; c. Flower, lateral view; d. Flower with two corolla lobes removed, showing the position of the corona basally enveloped by the corolla lobes; e. Flower, longitudinal section; f. Flower, viewed from above; g. Calyx lateral view; h. Calyx and ovaries, viewed from above; i. Corona, lateral view; j. Corona, top view; k. Flower, longitudinal section with the position of the guide rail highlighted in black; l. Anther and anther appendages (after removal of one staminal corona lobe). Photographs by M. Rodda. The parts of the gynostegium are labelled as:A = Anther;Aa =Anther appendage; C(is) = interstaminal corona lobe; Cs = Staminal corona lobe; G = Guide rail; Re = Retinaculum; S = Stigma; Sh = Stigma head.