Three Unusual New Species of Plukenetia (Euphorbiaceae) from Madagascar: Species Radiation and Convergent Evolution in P. sect. Madagascarienses

Abstract

Abstract— We describe three unusual new species of Plukenetia sect. Madagascarienses from eastern Madagascar based on morphology, pollen, and molecular data. Plukenetia analameranensis is unusual in the genus and section for its flat androecium of sessile anthers on a flat receptacle and is most similar to P. ankaranensis sharing obovoid stylar columns. Plukenetia antilahimenae and P. randrianaivoi are distinct in sect. Madagascarienses and among palaeotropical species for their elliptic or obovate-elliptic, pinnately veined leaf blades. They differ primarily in indumentum characters, including stems and inflorescence axes pubescent versus glabrous, and stipule size. Pollen of the new species (unknown in P. randrianaivoi) have reticulate or finely reticulate exines, while that of P. ankaranensis has a rugulate exine; this pollen morphology contrasts with that of all other palaeotropical species, which have foveolate exines. Phylogenetic analysis of nuclear ribosomal ETS and ITS data show that P. randrianaivoi is firmly embedded in the sect. Madagascarienses clade and sister to P. ankaranensis (the other two new species could not be sequenced). Based on these molecular and pollen results, together with floral characters (most importantly completely connate styles), we suggest that the three new species and P. ankaranensis form a subclade, sister to the other two Malagasy species, P. decidua and P. madagascariensis. With the description of these three new species, sect. Madagascarienses (6 spp.) becomes substantially more diverse morphologically. This species radiation in Madagascar resulted in the independent evolution of several leaf and pollen characters that previously were thought to distinguish the two major clades of Plukenetia, specifically pinnately veined leaf blades and reticulate pollen that look remarkably similar to the leaves and pollen of the neotropical pinnately veined clade. An emended description of section Madagascarienses, a key to the species of sect. Madagascarienses, and an updated key to the sections of Plukenetia are provided.