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Phylogeny and Biogeography of Wajira (Leguminosae): A Monophyletic Segregate of Vigna Centered in the Horn of Africa Region

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Abstract:

Evidence from chloroplast trnK and nuclear ribosomal ITS sequences and morphological data reveals that the monotypic legume genus Wajira is nested within a clade comprising the species of Vigna subgen. Macrorhynchus. This Wajira -containing clade is basally branching in a larger clade that contains many of the genera traditionally referred to as tribe Phaseoleae subtribe Phaseolinae. Wajira is thus recircumscribed to include Vigna subgen. Macrorhynchus. Given the heterogeneity of floral morphology of its constituent species, Wajira is apomorphically diagnosed by woody stems and a pollen brush that comprises an introrse linear array of unicellular hairs. This recircumscribed genus now comprises five species, one of which is described as new, Wajira danissana Three species require new nomenclatural combinations, Wajira grahamiana , Wajira praecox , and Wajira virescens . Wajira albescens , W. danissana , W. praecox, and W. virescens are woody climbers that are each narrowly distributed in the arid Somalia-Masai region characterized by sparse ground cover not subjected to seasonal burning. Wajira grahamiana has a thick woody subterranean rootstock that resprouts stems, and is widespread in the Sudano-Zambezian Region, southern India, and Sri Lanka, where grasslands subjected to seasonal burning predominate. This species is resolved in all phylogenetic analyses as derived from within the Somalia-Masai clade. An evolutionary rates analysis of trnK sequences suggests that the Wajira stem clade diverged from its closest relatives just over 10 million years ago, the extant diversification of the genus began around 6–7 million years ago, and Wajira grahamiana attained its widespread distribution during the last 2 million years.

Document Type: Regular Paper

DOI: http://dx.doi.org/10.1600/0363644042451035

Publication date: October 1, 2004

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