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Inflorescence development in the Vitis-Ampelocissus clade of Vitaceae: the unusual lamellate inflorescence of Pterisanthes
Article
Abstract
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Pterisanthes (Vitaceae) is a genus of c. 20 species of scandent climbers endemic to Southeast Asia with unusual lamellate inflorescences. Molecular phylogenetic analysis supports its relationship in the well-supported Vitis-Ampelocissus-Nothocissus-Pterisanthes clade (i.e. the Ampelocissus-Vitis clade). Shoot tips and floral buds were collected from wild and greenhouse-grown P. eriopoda at different developmental stages and were examined using epi-illumination, light and scanning electron microscopy. Inflorescence and floral ontogeny was studied to discover how the lamellate inflorescence evolved and to make morphological comparisons to infer relationships with closely related members of Vitaceae. The second-order branches in P. eriopoda are racemose and develop helically around the inflorescence axis in a similar fashion to Vitis and Ampelocissus. Inflorescence branching is restricted to the second order in P. eriopoda, whereas in Vitis and most Ampelocissus species subsequent branching orders culminate in the typical vitaceous determinate dichasium. In P. eriopoda subsequent lateral growth of the second-order branches combined with the inhibition of peduncle or pedicel formation and loss of dichasial branching results in the unique lamellae in Pterisanthes, on which the floral primordia arise directly in a helical pattern. Floral development in P. eriopoda is the same as in other genera of Vitaceae examined to date with initiation of floral whorls centripetally, the calyx ring developing first and calyx lobes fused to cover the petals and stamen primordia. Given the recent phylogenetic results that placed Pterisanthes firmly within Ampelocissus, the most likely scenario is that the Pterisanthes inflorescence is derived from the thyrse of an Ampelocissus-like ancestor and that the thyrse is a morphological synapomorphy of the Ampelocissus-Vitis clade. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179, 725-741.
