The remarkable morphological diversity of the palm subfamily Calamoideae provides a paradigm for evolutionary studies of palm structure and function. Phylogenetic relationships among the 22 calamoid genera are investigated here in simultaneous analyses of morphological data and DNA sequences from nuclear ITS regions and the chloroplast rps16 intron. The resultant hypotheses of relationship are used to explore morphological character evolution through an examination of character state optimisations. The evolution of habit and its associated characters is found to be highly homoplasious; for example, multiple origins of both the acaulescent and climbing growth forms have been identified. Similarly, life history and reproductive characters show complex patterns of evolution with few primary homology assessments proving to be effective judgements of synapomorphy. Many of these homoplasious characters were emphasized in the previous classification of the Calamoideae and consequently some non-monophyletic groups were recognized formally. We present a new classification in which a number of unexpected, group-defining characters, such as the number of pollen apertures, have been identified. The classification comprises three tribes and nine subtribes, including one newly described tribe Eugeissoneae. However, the morphology of many well supported clades remains poorly understood, creating further challenges for future studies in calamoid phylogeny.

Communicating Editor: Alan Whittemore