Colloquium: The flora of Madagascar: research needs and research progress
Wahlert, G. A. , Ballard, H. E. .
Rinorea section Verticillatae (Violaceae): An Endemic Malagasy Lineage of Tree-Violets.
Rinorea (Violaceae) is a pantropical genus of shrubs and small trees containing about 300 species. In the course of revising the ca. 40 species of Rinorea from Madagascar, an endemic lineage of opposite-leaved Rinorea has been identified. The Malagasy species can divided into two groups: 1) species with alternate leaves and 2) species with opposite leaves. This dichotomy reflects a biogeographic pattern among Malagasy and African Rinorea: the alternate-leaved Malagasy species are closely related to—or conspecific with—species in mainland Africa (e.g., R. ilicifolia, R. angustifolia, R. squamosa), whereas the opposite-leaved species (section Verticillatae Engl.) are endemic to Madagascar and the Comoros Islands. The opposite-leaved species have several morphological characters that are coordinate with the opposite leaf arrangement, including structure of the androecium, floral symmetry, plant architecture, and characters of the inflorescence. It is not yet known what species are most closely related to the opposite-leaved Malagasy and Comorian species. While there are ca. 33 opposite-leaved Rinorea species from the Neotropics, the species from mainland Africa and Asia are strictly alternate-leaved. Based on morphological divergence, there is ample justification to recognize the opposite-leaved Malagasy group as a segregate genus. However, a preliminary phylogeny inferred from chloroplast rbcL and trnL-F sequences places the opposite-leaved Malagasy species among a group of African taxa. In addition, the opposite-leaved Rinorea from Madagascar and the Comoros Islands are monophyletic and they show no close relationship to the opposite-leaved species from the Neotropics, suggesting multiple origins of opposite phyllotaxy in the mostly alternate-leaved Violaceae. Additional taxon sampling of African taxa for a chloroplast DNA phylogeny may lead to the identification of the closest relative to the opposite-leaved Malagasy and Comorian clade.
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1 - Ohio University, Department of Environmental & Plant Biology, Porter Hall, Richland Avenue, Athens, Ohio, 45701-2979, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Blair B/Gage
Date: Tuesday, July 29th, 2008
Time: 10:30 AM