Gardner, Andrew , Emshwiller, Eve .
Re-examining evolution of the North American bulb-forming Oxalis.
The genus Oxalis (Oxalidaceae) is species-rich and morphologically diverse, with shrubs, succulents, and weeds; species that form tubers, corms, and bulbs. Oxalis may be unique among the eudicots in forming bulbs, and has done so with gusto: Over two hundred bulb-forming species have radiated in southern Africa, and there is another more geographically expansive radiation in the New World. We are building a molecular phylogeny of this New World bulbous radiation and using it to structure ecological and morphological data. The North American component of the radiation has been emphasized in previous work. Early taxonomies of the North American bulbous Oxalis (Rose, 1906; Small, 1907) named over 60 species and created considerable disorder. In 1973, Melinda Denton greatly improved the taxonomy, settling on 25 species by recognizing heteroblastic leaf development and heterostyly, and by using numerous bulb, seed, and hair characters. Her work suggested that this group is polyphyletic with six evolutionary lines and that the tristylous breeding system common in Oxalis has evolved toward distyly. Here, we build a phylogeny focusing on the North American component of this radiation, using chloroplast and nuclear sequence data from at least 16 of 21 North American species and from a wide selection of South American bulbous and non-bulbous species. Our current sampling suggests that the North American bulbous Oxalis are a monophyletic radiation derived from South American bulb-bearing taxa. Additionally, there appear to be two major clades: one south of the Mexican transverse volcanic belt composed primarily of tristylous species and another north of this region composed primarily of distylous species. Although this work may contradict Dentonís suggestion that the North American bulbous Oxalis are polyphyletic, it will provide a new structure for understanding the evolution of heterostyly unavailable nearly 40 years ago.
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1 - University of Wisconsin Madison, Department of Botany, Birge Hall, 430 Lincoln Drive, Madison, Wisconsin, 53706-1381, USA
2 - University of Wisconsin-Madison, Department of Botany, Birge Hall, 430 Lincoln Drive, Madison, WI, 53706, USA
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Maybird/Cliff Lodge - Level C
Date: Wednesday, July 29th, 2009
Time: 8:00 AM