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Phylogenetics of Darwiniothamnus (Asteraceae: Astereae) – molecular evidence for multiple origins in the endemic flora of the Galápagos Islands

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Abstract Aim 

The aims of this study were (1) to investigate whether the two growth forms of Darwiniothamnus Harling (Asteraceae) originated from the colonization of a single ancestor, (2) to identify the closest relative(s) of Darwiniothamnus, and (3) to review molecular phylogenies from other plant groups to infer the origin of Galápagos endemics. Location 

Darwiniothamnus is endemic to the Galápagos Islands. Methods 

All putative relatives of Darwiniothamnus plus 38 additional species were included. Nucleotide sequences of the internal transcribed spacers of the nuclear ribosomal DNA were used for Bayesian and parsimony analyses. Results 

Darwiniothamnus is polyphyletic. Two species (D. lancifolius (Hook. f.) Harling and D. tenuifolius (Hook. f.) Harling) are woody shrubs that usually grow to 1–2 m in height; they belong to a clade composed of species otherwise restricted to the Caribbean. These two species are sister to Erigeron bellidiastroides Griseb., a herbaceous species endemic to Cuba. The third species (D. alternifolius Lawesson & Adsersen) is a perennial herbaceous plant, woody at the base and reaching only up to 50 cm in height. It is sister to two Chilean (Coquimbo–Valparaiso region) species that also have a perennial herbaceous habit: E. fasciculatus Colla and E. luxurians (Skottsb.) Solbrig. They are placed in an assemblage restricted to South America. The review of previous molecular phylogenetic studies revealed that two of the endemic genera and endemic species of three non-endemic genera have their closest relatives in South America. Endemic species belonging to three non-endemic genera have sister species in North America or the West Indies. One endemic genus and endemic species in three non-endemic genera have sister taxa with a widespread continental distribution, or their molecular phylogenies yielded equivocal results. Main conclusions 

The flora of Galápagos has affinities with both North America (including the Antilles) and South America. Darwiniothamnus exhibits both patterns: two species of this genus are sister to a taxon endemic to Cuba, supporting a connection between the Cocos plate and the West Indies; the third species, D. alternifolius, provides a link with the Coquimbo–Valparaiso region, suggesting a biogeographical connection between the Nazca plate and southern South America.
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Keywords: Caribbean Islands; DNA markers; Darwiniothamnus; Neotropics; Pacific Islands; critically endangered species; oceanic islands; phylogeography; trans-oceanic dispersal

Document Type: Research Article

Affiliations: 1: 2925 Hartwood Drive, Fort Worth, TX, USA 2: Center for Plant Conservation, Fairchild Tropical Botanic Garden, Coral Gables, FL, USA 3: Department of Biology, 180 Lewis Science Center, University of Central Arkansas, Conway, AR, USA 4: Charles Darwin Research Station, Puerto Ayora, Isla Santa Cruz, Galápagos, Ecuador

Publication date: 01 June 2009

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