Systematics Section / ASPT
Koopman, Margaret M. , Smith, Stacey D. , Baum, David A. .
Preliminary evidence for the monophyly and diversification within the Malagasy Hibisceae.
Eumalvoideae (which approximates the traditional Malvaceae) has been shown by molecular phylogenetic work to be a clade of about 1700 species whose basal branches are Australasian mangroves and littoral treelets that have traditionally been placed in the (paraphyletic) tribe Hibisceae. Madagascar boasts a significant radiation of Hibiscus, including most notably 13 species in H. sect. Azanzae (Hochreutiner) and 21 species in six endemic genera that are generally assigned to Hibisceae (Helicteropsis, Humbertianthus, Humbertiella, Jumelleanthus, Megistostegium and Perrierophytum). These genera exhibit unique morphological features. Megistostegium, for example, has an enlarged and brightly colored epicalyx while Humbertiella exhibits unusual staminal glands. The genus Macrostelia is disjunct between Australia and Madagascar. In an attempt to elucidate the placement of these taxa within Eumalvoideae matK and ndhF sequences were obtained for two Malagasy endemic genera (Megistostegium and Humbertiella) and Malagasy representatives of Hibiscus, Macrostelia and Kosteletzkya. The rapid evolution within Eumalvoideae permitted good resolution. MatK/ndhF data strongly support a clade that includes all but one of the accessions from Madagascar. The endemic genera form a clade embedded within a grade of Malagasy members of Hibiscus sect. Azanzae and Kosteletzkya. The data suggest a close relationship between Humbertiella and Megistostegium, a result that gains support from morphology (both have an enlarged cushion-like anther connective, Dorr, 1990) and ecology (both occur in xeric scrub and desert settings; all Megistostegium and some Humbertiella are bird pollinated). However, these two taxa differ greatly in their flowers. The Malagasy accession of Macrostelia is sister to Australian members of this group, suggesting long-distance dispersal. Further sampling of the endemic genera and throughout Hibiscus sect. Azanzae is clearly necessary.
1 - University of Wisconsin-Madison, Botany, 430 Lincoln Drive, Madison, Wisconsin, 53706-1381, USA
Presentation Type: Poster
Location: Special Event Center (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 12:30 PM