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Madagascar is surrounded by archipelagos varying widely in origin, age and structure. Although small and geologically young, these archipelagos have accumulated disproportionate numbers of unique lineages in comparison to Madagascar, highlighting the role of waif-dispersal and rapid in situ diversification processes in generating endemic biodiversity. We reconstruct the evolutionary and biogeographical history of the genus Psiadia (Asteraceae), a plant genus with near equal numbers of species in Madagascar and surrounding islands. Analyzing patterns and processes of diversification, we explain species accumulation on peripheral islands and aim to offer new insights on the origin and potential causes for diversification in the Madagascar and Indian Ocean Islands biodiversity hotspot. Our results provide support for an African origin of the group, with strong support for non-monophyly. Colonization of the Mascarenes took place by two evolutionary distinct lineages from Madagascar, via two independent dispersal events, each unique for their spatial and temporal properties. Significant shifts in diversification rate followed regional expansion, resulting in co-occurring and phenotypically convergent species on high-elevation volcanic slopes. Like other endemic island lineages, Psiadia have been highly successful in dispersing to and radiating on isolated oceanic islands, typified by high habitat diversity and dynamic ecosystems fuelled by continued geological activity. Results stress the important biogeographical role for Rodrigues in serving as an outlying stepping stone from which regional colonization took place. We discuss how isolated volcanic islands contribute to regional diversity by generating substantial numbers of endemic species on short temporal scales. Factors pertaining to the mode and tempo of archipelago formation and its geographical isolation strongly govern evolutionary pathways available for species diversification, and the potential for successful diversification of dispersed lineages, therefore, appears highly dependent on the timing of arrival, as habitat and resource properties change dramatically over the course of oceanic island evolution.

Erigeron geiseri Shinners is a tap-rooted herbaceous daisy occurring from south-eastern Texas to southern Oklahoma. Our study of pollen quality from 67 herbarium specimens supports the hypothesis that the species comprises sexual diploid populations, restricted to southern locations, and polyploid, putatively apomictic, populations that are widespread. We successfully amplified and sequenced ITS and ETS spacer regions of nrDNA for five specimens (two putative sexual diploids, three putative apomictic polyploids). Phylogenetic analysis conducted using maximum likelihood and Bayesian methods support a topology showing that 1) sexual and apomictic populations of E. geiseri form a well-supported monophyletic group, and, 2) E. geiseri is sister to E. strigosus of eastern North America. The results support the classification of E. geiseri with E. strigosus in E. sect. Phalacroloma. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Complex geographical distribution patterns and agamospermy have united to obscure systematic relationships in the genus Erigeron (400+ species). Sequence data were analyzed from the internal transcribed spacer region of nrDNA (ITS) and 5.8S cistron for 77 taxa including 63 Erigeron species. Results support the North American origin of Erigeron and document that Aphanostephus, Conyza, and three small genera restricted to South America ( Apopyros, Hysterionica, Neja) are all derived from within Erigeron. Phylogenetic data indicate that agamospermy has arisen at least three times in Erigeron and that autogamy has evolved independently in Conyza and in E. sect. Trimorpha. [ABSTRACT FROM AUTHOR]