Dalechampia

Results from recent collaborative phylogenetic studies in the pantropical genus Dalechampia (Euphorbiaceae)

Since 1994, Bruce Baldwin, Bridget Wessa, and W. Scott Armbruster (Trondheim University, Norway) have collaboratively studied molecular phylogenetics of Dalechampia (Euphorbiaceae), a pantropical genus of ca. 120 species. They emphasized sampling of the poorly-known paleotropical taxa, in part for purposes of taxonomic revision. Bruce and Scott conducted plant collecting and pollination studies in Madagascar and Scott worked in Africa, the two major centers of Dalechampia diversity in the paleotropics (samples of neotropical taxa and one Asian species were obtained earlier). DNA sequences of the ITS region of 18-26S nuclear rDNA and of the trnK intron of cpDNA were obtained from one or more populations of 42 species spanning all sections and geographical/morphological groups in the genus. Phylogenetic analyses based on the acquired data were conducted and resulting data used to analyze historical biogeography, character evolution, and pollination-system evolution in Dalechampia.

Results of phylogenetic analyses and character/ecological reconstructions support: (1) a neotropical origin of Dalechampia, with dispersal to Africa followed by dispersal from Africa to Madagascar and Asia, (2) a novel shift from specialized to generalized pollination (i.e., resin- to pollen-reward) in Madagascar, associated with resin-gland loss (through loss of bractlet fusion) and evolution of inflorescence architecture closely paralleling that of the neotropical pollen-reward taxa, (3) evolution of buzz-pollination (first report for Euphorbiaceae) in Madagascar, apparently by neoteny in staminate flower development, (4) three origins of fragrance-reward in neotropical Dalechampia, and (5) recognition of two undescribed species in Africa and Madagascar. Continuing collaborative research with Armbruster (with his remaining funds) will emphasize expanding sampling of Asian taxa and conducting combined phylogenetic analyses of morphological and molecular data for additional resolution of morphological evolution and for taxonomic revision of the genus.

For more on this fascinating genus and the research results of their recent studies see the following paper and abstracts:

Armbruster, W. S. & B. G. Baldwin. 1998. Switch from specialized to generalized pollination. Nature 394: 632.

Armbruster, W. S. & B. G. Baldwin. 1997. A neotenous origin of buzz pollination in Malagasy Dalechampia vines. Bull. Ecol. Soc. Amer. 78 (4, supplement): 47.

Baldwin, B. G., W. S. Armbruster & B. L. Wessa. 1996. Molecular evidence for independent origins of similar pollination systems and inflorescence architectures in New World and Madagascar Dalechampia (Euphorbiaceae). Amer. J. Bot. 83 (6, supplement): 139.

This material is based upon work supported in part by the National Science Foundation under Grant No. DEB-9596019 to BGB.