Phylogenetic relationships between Clerodendrum (Lamiaceae) and other Ajugoid genera inferred from nuclear and chloroplast DNA sequence data

Abstract

Over the last two centuries the circumscription of the large, pan-tropical genus Clerodendrum (Lamiaceae) has changed frequently, as different authorities have added or removed taxa on the basis of various morphological characters. With the development of molecular methods for systematic research the process of circumscribing taxa has become increasingly analytical. When morphology signals the possibility that taxa are closely related, molecular methods can be used to test the hypothesis objectively. Aegiphila, Amasonia, Huxleya, and Kalaharia are similar morphologically to Clerodendrum. In this paper we use nuclear ribosomal ITS and chloroplast ndhF sequence data to clarify the positions of these four genera relative to Clerodendrum. We show that the Australian monotypic genus Huxleya evolved from within Clerodendrum. Accordingly, we sink Huxleya into Clerodendrum and make a new combination, Clerodendrum linifolium.