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(American Journal of Botany. 2006;93:1065-1080.)
© 2006 Botanical Society of America, Inc.

Systematics and Phytogeography

Homoplasious character combinations and generic delimitation: a case study from the Indo-Pacific arecoid palms (Arecaceae: Areceae)1

Maria Vibe Norup5, John Dransfield, Mark W. Chase, Anders S. Barfod, Edwino S. Fernando and William J. Baker

2Department of Systematic Botany, University of Aarhus, Ny Munkegade, Building 540, 8000 Aarhus, Denmark; 3Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, UK; 4Department of Forest Biological Sciences, The University of the Philippines, Los Baños, College, 4031 Laguna, Philippines

ABSTRACT

The complex distributions of morphological character states in the Indo-Pacific palm tribe Areceae (Arecaceae; Arecoideae) are potentially challenging for the delimitation of its genera. In the first exhaustive sampling of all 65 genera of the Areceae, we examined relationships of two of the tribe's most problematic genera, Heterospathe and Rhopaloblaste, using portions of the low-copy nuclear genes phosphoribulokinase (PRK) and RNA-polymerase II subunit B (RPB2). Both genera fell within a highly supported clade comprising all Areceae genera, but are clearly unrelated. Rhopaloblaste was strongly supported as monophyletic and is most closely related to Indian Ocean genera. Heterospathe was resolved with strong support within a clade of western Pacific genera, but with the monotypic Alsmithia nested within it. Ptychosperma micranthum, which has previously been included in both Heterospathe and Rhopaloblaste, is excluded from these and from Ptychosperma, supporting its recent placement in a new genus Dransfieldia. Morphological comparisons indicate that the crownshaft is putatively synapomorphic for the Areceae with numerous reversals within the clade and some independent origins elsewhere. The putative diagnostic characters of Heterospathe show high levels of homoplasy, and the genus can only be distinguished by a suite of characters, whereas Rhopaloblaste is more clearly defined. Our results have implications not only for the two genera in focus, but have also been influential for the new classification of the Areceae.

Key Words: Arecaceae • biogeography • Heterospathe • low-copy nuclear DNA • molecular phylogenetics • morphology • pseudomonomery • Rhopaloblaste






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