Jaffrea, a new genus of Rhamnaceae endemic to New Caledonia, with notes on Alphitonia and Emmenosperma

Abstract

Molecular phylogenetic and morphological data show that two species of Rhamnaceae endemic to New Caledonia, Alphitonia xerocarpa and A. erubescens, are misplaced. They form a clade that is sister to Emmenosperma, and they differ from Alphitonia s.s. in their indumentum, venation, lower leaf surface, flowers, fruits and seeds. Although morphologically closer to Emmenosperma, both their flowers and fruits are distinct from those of Emmenosperma s.s., and so a new genus, Jaffrea H. C. Hopkins & Pillon, is described to accommodate them, and the combinations Jaffrea xerocarpa (Baill.) H. C. Hopkins & Pillon and Jaffrea erubescens (Baill.) H. C. Hopkins & Pillon are published. Members of this new genus have a conical hypanthium, petals somewhat incurved at anthesis, a thick disc that is either ± lumpy or annular but not or only partly covering the semi-inferior ovary, and fruits that are ovoid-ellipsoid, strongly beaked and tardily dehiscent. As in Emmenosperma and most species of Alphitonia, the seeds in Jaffrea can remain attached to the base of the fruit after most of the pericarp has fallen. Alphitonia is now represented in New Caledonia by a single species, A. neocaledonica, and its nomenclature and types are reviewed. The generic description of Alphitonia is amended to include the unique fruits of the New Guinean endemic A. macrocarpa, which are much larger than those of its congeners, strongly beaked, lacking a mealy endocarp, and with seeds that fall before the persistent valves. Relationships within Emmenosperma s.l., especially the affinities of E. papuanum and E. micropetalum, require further investigation.