A reconsideration of the generic circumscription of Heterostemma Wight & Arn. (Asclepiadaceae) and a new species from India

Abstract

Heterostemma Wight & Arn. (Asclepiadaceae) and a new species from India. Heterostemma vasudemni Swarupanandan & Mangaly, a new species belonging to Asclepiadaceae is described and illustrated. The discoid‐urceoloate corolla and the staminal coronal scales with a ventral appendage show this species to be intermediate between the two genera Heterostemma and Oianthus. Basically, the concepts of the two genera differ only in a pair of characters which, in the light of the new species seem not to be particularly diagnostic. On this basis it is proposed to merge the two genera together, by reducing Oianthus as a section under Heterostemma. Consequently, three new combinations are proposed. Examination of recent collections extends the distribution of what was 0. decanense, earlier considered to be endemic to Maharashtra, further south to Kerala.

Magnoliopsida, Gamopetalae, Gentianales, Asclepiadaceae, Heterostemma deccanense (Talb.) Swarup & Mangaly: distribution, extension and geographic distribution map

“…Hence, Nayar and Sastry (1987) included it in Red Data Book of Indian Plants, under endangered and possibly extinct category. Swarupanandan et al (1989), while studying generic circumscription of Heterostemma, Oianthus deccanensis is included in the genus Heterostemma. Sasidharan and Swarupnandan (1994) reported it as a rediscovered species from tropical moist deciduous forests of Peechi in Thrissur district of Kerala (Southern Western Ghats), where they located very few individuals.…”

Checklist and typification of Heterostemma (Apocynaceae, Asclepiadoideae, Ceropegieae)

“…The genus comprises of 30 to 40 species found in Australia, Bangladesh, China, India, Indonesia, Laos, Malaysia, Myanmar, Nepal, New Guinea, Philippines, Sri Lanka, Thailand, Vietnam and Western Pacific Islands (Swarupanandan et al 1989, Forster 1992. The species of Heterostemma are characterised by terrestrial twining habit, thin (non-succulent) lanceolate to orbicular leaves, extraaxillary pseudo-umbelliform to raceme-like inflorescences, rotate to urceolate corollas, staminal corona with five basally connate lobes spreading or sub-erect, with or without an adaxial horned appendage, poorly developed terminal anther appendages, erect subquadrate to oblong pollinia with a germinating mouth on the inner margin, slender single or paired follicles, winged seeds with a long coma (Swarupanandan et al 1989, Forster 1992, Jagtap & Singh 1999.…”

“…Hooker 1883b, Costantin, 1912, Backer & Bakhuizen van den Brink 1965, Swarupanandan et al 1989, Forster 1992, Jagtap & Singh 1999, two new species have been published in recent years (Lin et al 2010, Tran & Kim 2010 and a generic revision is in preparation (Rodda in prep. ).…”

“…Oianthus Bentham (1876Bentham ( : 79, t. 1191) was synonymised with Heterostemma by Swarupanandan et al (1989) and Heterostemma sect. Oianthus Swarupan.…”

“…Heterostemma sect. Oianthus was indicated as endemic to South Asia (Swarupanandan et al 1989), however also Heterostemma fimbriatum King & Gamble (1908: 558) from Peninsular Malaysia has urceolate corollas and may belong to the section.…”