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Evolution of Tidestromia (Amaranthaceae) in the deserts of the southwestern United States and Mexico

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Tidestromia (Gomphrenoideae, Amaranthaceae) is a monophyletic genus restricted to deserts of North America with the highest levels of endemism centered in the Chihuahuan desert. Tidestromia is morphologically distinct from related genera which caused researchers difficulty in identifying its phylogenetic affinities. Recent molecular phylogenetic evidence suggests that a monophyletic Tidestromia is related to Alternanthera and Pedersenia in a well-supported linage referred to as the Alternantheroid clade. Preliminary species circumscription of Tidestromia suggested six species, two subspecies and two varieties. However, this study revealed problems in the current infraspecific classification based on morphology. The current study aims at testing the phylogenetic relationships within the genus using nuclear (ITS), chloroplast (rpl16, trnL-F), and morphological data and examine the role that soils, climate, and habitat have had on speciation in the genus. Earlier researchers hypothesized these environmental features were reproductive barriers driving speciation; however, incongruency between the chloroplast and nuclear datasets with additional support from previous cytogenetic data suggests that hybrid speciation has played a larger role. The total evidence results in a fully resolved ingroup and suggests that all infraspecific taxa are distinct species requiring nomenclatural taxonomic changes. Contrary to previous findings, the annual habit has evolved twice in the genus.


Document Type: Research Article

Publication date: 2010-02-01

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