The New Genus Calyptranthera (Asclepiadaceae) from Madagascar

Abstract

A species previously identified as Toxocarpus caudiclavus Choux (Asclepiadaceae, Secamoneae) is outside the morphologic and phylogenetic bounds of this genus. Instead, it is more closely related to the Malagasy endemic genus Pervillea Decaisne (Secamoneae), with which it shares some gynostegium characters. Toxocarpus caudiclavus differs from Pervillea, however, in several characters and is best placed in a new genus, Calyptranthera, which is herein described and illustrated. During a survey of the tribe Secamoneae in Madagascar for the Flore de Madagascar et des Comores, I came across a taxon of Toxocarpus, TI caudiclavus Choux, that has been misplaced. Toxocarpus caudiclavus was described by Choux (1914: 415), who with some hesitation placed the taxon in this genus. Toxocarpus Wight & Arnott is a primarily Asian genus, with a few species described from the African mainland and Madagascar. The type species, T kleinii Wight & Amrnott, which is distributed in India and Sri Lanka, is characterized by a two-parted dorsiventrally flattened corona lobe, a stigma head placed directly on the ovary with a thick lower part and a long thin upper part distinctly projecting above the staminal column. The likewise paleotropical Secamone R. Brown, the other large genus within the tribe Secamoneae, also described from Asia, differs primarily from Toxocarpus by having small flowers, laterally compressed corona lobes, and a short stigma head that does not project above the staminal column. Outside Asia, however, the distinction between these two genera is less marked, and several species of Toxocarpus might be better placed in Secamone, or both taxa may need to be divided into several smaller monophyletic genera (for discussion and references, see Klackenberg, 1992: 8). In Madagascar none of the diagnostic characters for the two genera holds true, and most Malagasy Secamoneae have hitherto been included in Secamone sensu lato. However, a handful of distinctly different Malagasy taxa with large flowers and dorsiventrally flattened corona lobes have been considered to be congeneric with the Asian Toxocarpus. Recent studies have shown that the Malagasy Toxocarpus is a paraphyletic group composed of species better placed in at least three other genera, i.e., Secamone s.1. (Klackenberg, 1992: 20), Pervillea (Klackenberg, 1995 and in prep.) and Calyptranthera (see below). Toxocarpus caudiclavus fits neither in Toxocarpus s. str. as it is circumscribed in Asia, nor in Secamone s.1. as it is known in Madagascar. It differs by its long projecting connectives and by having a discoid stigma head abruptly narrowed into a style and topped by a short broad upper part. This structure is found also in, e.g., Periplocaceae and the Malagasy endemic genus Pervillea, but not in Secamone/Toxocarpus (see above). Furthermore, in T caudiclavus the four pollinia are adnate to a very thin U-like folded corpusculum without caudicle. These three characters, which distinguish Toxocarpus caudiclavus from Toxocarpus/Secamone, ally it, however, to Pervillea. Pervillea was described by Decaisne (1844: 613) as a monotypic genus (P tomentosa), but was later included in Toxocarpus by Jumelle and Perrier de la Bathie (1907: 389, 1908: 214). However, it has recently been shown that due to several distinguishing characters, particularly the long projecting connectives, this taxon must be excluded from Toxocarpus, and Pervillea has been reinstated as a separate genus (Klackenberg, 1995). Furthermore, Pervillea is no longer monotypic but comprises, in addition to P tomentosa, two more species: P. decaryi (Choux) Klackenberg (= Toxocarpus decaryi Choux) and P. venenata (Baillon) Klackenberg ( Menabea venenata Baillon) (Klackenberg 1995 and in prep.). Toxocarpus caudiclavus differs from Pervillea and Toxocarpus/Secamone by the fused connectives forming a calyptra at the top of the gynostegium, the club-shaped appendages on long strings at the top of the prolonged connectives, the filaments with cuplike projections below the anther wings forming the pollinium entrance, the short recurved corona lobes, and the thin hairy submarginal fold at the corolla lobes. None of these features have been observed elsewhere in the tribe Secamoneae. Toxocarpus caudiclavus also lacks the unique feature of distinctly curled leaf hairs with much reduced or NovoN 6: 25-27. 1996. This content downloaded from 207.46.13.176 on Mon, 20 Jun 2016 06:15:47 UTC All use subject to http://about.jstor.org/terms