Molecular Phylogenetic and Morphological Evidence Supports Recognition of Gereaua, a New Endemic Genus of Sapindaceae from Madagascar.

Abstract

A recent worldwide phylogeny of Sapindaceae inferred from nuclear and plastid DNA regions segregated the Malagasy Haplocoelum perrieri Capuron from the African Haplocoelum foliosum (Hiern) Bullock. Additional phylogenetic analyses conducted here (including material of Haplocoelum inopleum Radlk., the generic type) supported the result from the previous analysis and showed that maintaining a broad circumscription of Haplocoelum to include the Malagasy species would render the genus polyphyletic. To maintain monophyly, it is necessary to exclude H. perrieri, which we transfer to a new, monotypic genus, described here as Gereaua. This taxon is easily distinguished from the species retained in Haplocoelum by the following morphological characters: (1) sexually dimorphic inflorescences in racemules (vs. monomorphic inflorescences in fascicule of cymes); (2) 2-locular ovary (vs. 3-locular ovary); (3) rudimentary pistillode in staminate flowers (vs. no pistillode in staminate flowers); (4) corolla with 4 or 5 petals (vs. apetalous); (5) pubescent fruit (vs. glabrous fruit). Relationships between the new genus and its most closely related genera, included in the Macphersonia group, are discussed in light of molecular, morphological and biogeographic evidence. A preliminary threat assessment of Gereaua perrieri using the IUCN Red List criteria indicates a status of Least Concern.