Systematics Section / ASPT
Koopman, Margaret M. , Baum, David A. .
A phylogenetic analysis of the Hibisceae (Malvaceae) radiation on Madagascar.
Recent molecular systematic studies have shown that Hibisceae (Malvaceae) and its largest genus, Hibiscus, as traditionally circumscribed are paraphyletic. Madagascar boasts a substantial radiation within Hibisceae, whose relationships to other elements of Hibiscus s.l. are poorly known. In addition to 20 species in five endemic genera (Helicteropsis, Humbertiella, Jumelleanthus, Megistostegium and Perrierophytum) the island harbors approximately 32 endemic species traditionally assigned to Hibiscus s.l., as well as endemic representatives of two other widespread genera: Macrostelia (including Humbertianthus) and Kosteletzkya. Molecular data was used to determine the number of invasions of Madagascar and to assess the relationships among the endemic taxa. mat K and ndh F sequences were obtained for representatives of the endemic genera as well as Malagasy Hibiscus, Macrostelia and Kosteletzkya. Phylogenetic analysis of these data along with a sampling of outgroups and other lineages of Hibisceae, strongly supports one major Malagasy radiation. However, the Malagasy Macrostelia, which have radiated exclusively in the eastern littoral rainforests, appear to be related to Australian taxa formerly also assigned to Macrostelia (but recently transferred to Hibiscus) rather than to the main Malagasy clade. The major clade includes the endemic genera embedded within a grade of Malagasy members of Hibiscus and Kosteletzkya. In contrast to Macrostelia, members of this clade are restricted to dry habitats mainly in western and southern Madagascar. The historical recognition of these segregate genera reflects the existence of considerable morphological diversity within the group. Humbertiella, for example, has an inflated or petaloid anther-connective whereas Megistostegium possesses a red, petaloid epicalyx. In part this morphological diversity likely reflects differences in pollination mode and ecological specialization for desert environments. Further work is needed to clarify patterns of morphological evolution in the major Malagasy clade and to shed light on the timing of its invasion and radiation in Madagascar.
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1 - University of Wisconsin Madison, Department of Botany, Birge Hall, 430 Lincoln Drive, Madison, Wisconsin, 53706-1381, USA
Presentation Type: Oral Paper
Date: Tuesday, August 16th, 2005
Time: 4:00 PM