Abstract
The pan-tropical genus Clerodendrum s.l. is polyphyletic. While subgenus Cyclonema and section Konocalyx have been removed to the resurrected genus Rotheca, and the monotypic genus Huxleya has been combined into Clerodendrum in recent studies, whether the presently circumscribed Clerodendrum is monophyletic still remains unclear, particularly in relation to the currently recognized American genera Aegiphila, Amasonia, and Tetraclea. This phylogenetic study employs four relatively fast-evolving chloroplast DNA regions, trnT-L, trnL-F, trnD-T, and trnS-fM, to clarify the generic boundary of Clerodendrum and its relationship to allied genera. The results corroborate previous studies that there are three well-supported clades in the currently recognized Clerodendrum: an Asian clade, an African clade, and an Oceanic Coastal clade. The Asian clade and African clade are sister groups and together form a monophyletic group. However, the Oceanic Coastal clade is more closely related to the three New World genera, which together are supported as a monophyletic group, than it is to the other two Clerodendrum clades. This suggests that the currently recognized Clerodendrum is paraphyletic in relation to the New World clade. We propose to separate the Oceanic Coastal clade in reviving the genus, Volkameria, and restrict Clerodendrum to the Asian and African clades. Within the New World clade, the relationship between Aegiphila, Amasonia, and Tetraclea are poorly resolved. Low sequence divergences, particularly in the African Clerodendrum clade, indicate a recent diversification of these taxa and suggest that dispersal rather than vicariance accounts for the geographic distribution of Clerodendrum s.s., Volkameria, and their New World relatives.