Phylogeny and Historical Biogeography of the Genus Bromheadia (Orchidaceae)

Abstract

The phylogeny of the orchid genus Bromheadia (26 species) has been analyzed using 27 characters. Bromheadia is a monophyletic genus with one very distinctive apomorphy, the shape of the stipe of the pollinia. Because of the distinct morphology of the genus only the genus Claderia seemed to resemble Bromheadia sufficiently to act as an outgroup. The analysis resulted in a single cladogram with a length of 78 steps. Bromheadia has traditionally been subdivided into two sections. Section Aporodes appeared to be monophyletic (unique characters are laterally flattened leaves and the presence of sterile bracts). Section Bromheadia is paraphyletic and should include the other section to be monophyletic, or alternatively, it has to be subdivided into three monophyletic groups. A historical biogeographic analysis regrettably had to unite all distinct areas in Borneo due to imprecise data. It resulted in a mainly sympatric speciation scenario for Bromheadia, with one vicariance event, and several dispersals. The method used, Brooks' Parsimony Analysis, is questioned for its seemingly artificial rooting (all-zero area) and consequently, usually sequential splitting of areas with an increasing number of present taxa and ancestral taxa. The Ancestral Area method of Bremer mainly indicated Borneo as the only area of origin of Bromheadia.