The Systematics Of Dombeya Cav. And Its Near Relatives (Dombeyaceae)

The species-rich and morphologically diverse genus Dombeya Cav. (Dombeyaceae) is a spectacular example of the remarkable diversity of the biota of Madagascar where evolution has followed a unique trajectory. Like other large genera, Dombeya remains a taxonomic hurdle in understanding the Malagasy flora. Over 5000 base pairs of sequence data from five noncoding plastid markers and ITS of Dombeya and relatives, including 87 accessions from 68 species and 10 genera, are used to investigate patterns of molecular evolution in Dombeya and hypothesize a phylogeny using parsimony and Bayesian methods. These results are synthesized with morphological observations and used as a means for evaluating the generic delimitation and infrageneric taxonomy of Dombeya. Plastid introgression is invoked to explain incongruence between closely related taxa in plastid versus ITS phylogenies. The topology of the combined analysis of all molecular regions generally corresponds with morphology and includes four major groups. The majority of the Malagasy species and all African species of Dombeya sampled form a monophyletic clade and are defined as Dombeya sensu stricto. A second clade includes winged-seed dombeyoids: the highly autapomorphic Eriolaena, Helmiopsis, Helmiopsiella and D. linearfolia. This molecular data and morphology support the transfer of D. linearifolia to Helmiopsis. A third, morphologically coherent clade of D. subsect. Macranthae plus D. moratii are consistently excluded from Dombeya s. str. in both plastid and nuclear phylogenies; these taxa are segregated from Dombeya as the new genus Andringitra. The fourth clade contains only Mascarene endemics: Trochetia, Ruizia, and a portion of the Dombeya from these islands. Differing relationships between these four groups in plastid versus ITS phylogenies suggest incomplete lineage sorting, possibly indicating the rapid divergence of these lineages. Molecular data provide little support for the infrageneric taxonomy of Dombeya. Revisionary work needed in Dombeya is begun with a study of section Astrapaea, a group distinguished by pendulous inflorescences and long staminal tubes. Broader species circumscriptions than those previously adopted are proposed because traditional taxonomic characters in the section overlap between species and sometimes vary within individuals or populations. One new species, D. gautieri, and one new subspecies, D. cannabina subsp. antsifotrensis, are described

Recent assembly of the Cerrado, a neotropical plant diversity hotspot, by in situ evolution of adaptations to fire

The relative importance of local ecological and larger-scale historical processes in causing differences in species richness across the globe remains keenly debated. To gain insight into these questions, we investigated the assembly of plant diversity in the Cerrado in South America, the world's most species-rich tropical savanna. Time-calibrated phylogenies suggest that Cerrado lineages started to diversify less than 10 Mya, with most lineages diversifying at 4 Mya or less, coinciding with the rise to dominance of flammable C4 grasses and expansion of the savanna biome worldwide. These plant phylogenies show that Cerrado lineages are strongly associated with adaptations to fire and have sister groups in largely fire-free nearby wet forest, seasonally dry forest, subtropical grassland, or wetland vegetation. These findings imply that the Cerrado formed in situ via recent and frequent adaptive shifts to resist fire, rather than via dispersal of lineages already adapted to fire. The location of the Cerrado surrounded by a diverse array of species-rich biomes, and the apparently modest adaptive barrier posed by fire, are likely to have contributed to its striking species richness. These findings add to growing evidence that the origins and historical assembly of species-rich biomes have been idiosyncratic, driven in large part by unique features of regional- and continental-scale geohistory and that different historical processes can lead to similar levels of modern species richness

One thousand plant transcriptomes and the phylogenomics of green plants

Abstract: Green plants (Viridiplantae) include around 450,000–500,000 species1, 2 of great diversity and have important roles in terrestrial and aquatic ecosystems. Here, as part of the One Thousand Plant Transcriptomes Initiative, we sequenced the vegetative transcriptomes of 1,124 species that span the diversity of plants in a broad sense (Archaeplastida), including green plants (Viridiplantae), glaucophytes (Glaucophyta) and red algae (Rhodophyta). Our analysis provides a robust phylogenomic framework for examining the evolution of green plants. Most inferred species relationships are well supported across multiple species tree and supermatrix analyses, but discordance among plastid and nuclear gene trees at a few important nodes highlights the complexity of plant genome evolution, including polyploidy, periods of rapid speciation, and extinction. Incomplete sorting of ancestral variation, polyploidization and massive expansions of gene families punctuate the evolutionary history of green plants. Notably, we find that large expansions of gene families preceded the origins of green plants, land plants and vascular plants, whereas whole-genome duplications are inferred to have occurred repeatedly throughout the evolution of flowering plants and ferns. The increasing availability of high-quality plant genome sequences and advances in functional genomics are enabling research on genome evolution across the green tree of life