A Molecular and Morphological Survey of Generic Limits of Acsmithia and Spiraeanthemum (Cunoniaceae)

Abstract

A phylogenetic analysis was conducted on the tribe Spiraeanthemeae (Cunoniaceae) to clarify relationships of Acsmithia and Spiraeanthemum. Three molecular markers, one plastid region (trnL intron and trnL-trnF intergenic spacer) and two nuclear single copy genes (ncpGS and PHYC), were sequenced for this purpose. The independent analysis of the three markers and a combined analysis all showed that Acsmithia is paraphyletic since Spiraeanthemum is nested within it. A morphological survey of all species in the tribe confirmed the existence of two groups within Acsmithia. One comprises the species from Australia, New Guinea, and A. densiflora from New Caledonia and is characterised by multiple ovules per carpel. The other group contains all the remaining New Caledonian species plus A. vitiensis from Fiji and is characterized by a single ovule per carpel. The study shows that characters previously used to distinguish Acsmithia and Spiraenthemum, phyllotaxy and sexual system, are homoplasious as in several other groups of Cunoniaceae. A broad circumscription of the genus Spiraeanthemum is adopted here that includes the species formerly placed in Acsmithia. Two new combinations are proposed: Spiraeanthemum collinum and Spiraeanthemum meridionale. Spiraeanthemum austrocaledonicum is considered a synonym of Spiraeanthemum densiflorum.