No abstract

Species radiations, despite immense phenotypic variation, can be difficult to resolve phylogenetically when genetic change poorly matches the rapidity of diversification. Genomic potential furnished by palaeopolyploidy, and relative roles for adaptation, random drift and hybridisation in the apportionment of genetic variation, remain poorly understood factors. Here, we study these aspects in a model radiation, Syzygium, the most species-rich tree genus worldwide. Genomes of 182 distinct species and 58 unidentified taxa are compared against a chromosome-level reference genome of the sea apple, Syzygium grande. We show that while Syzygium shares an ancient genome doubling event with other Myrtales, little evidence exists for recent polyploidy events. Phylogenomics confirms that Syzygium originated in Australia-New Guinea and diversified in multiple migrations, eastward to the Pacific and westward to India and Africa, in bursts of speciation visible as poorly resolved branches on phylogenies. Furthermore, some sublineages demonstrate genomic clines that recapitulate cladogenetic events, suggesting that stepwise geographic speciation, a neutral process, has been important in Syzygium diversification.

Rachunia, a new genus of Gesneriaceae from Thailand, is described with a single species, Rachunia cymbiformis. Its relationship to the rest of subtribe Didymocarpinae is investigated through a phylogenetic study based on Bayesian Inference and Parsimony analyses of nuclear ITS and plastid trnL‐trnF (intron‐spacer) sequences. Morphologically, Rachunia differs from the related genera Codonoboea in the large boat‐shaped bracts and orthocarpic vs plagiocarpic fruit; from Microchirita in the bracts, wiry vs fleshy stem, the campanulate vs tubular corolla and the clavate vs chiritoid stigma, and from Henckelia in the clavate vs chiritoid stigma, large boat‐shaped bracts in the inflorescence, free and imbricate sepals, short and campanulate corolla, clavate stigma, and relatively robust orthocarpic fruit.

Five new species of Henckelia are described, two from Myanmar: Henckelia campanuliflora and H. candida, and the others from Thailand: H. amplexifolia, H. nakianensis and H. dasycalyx. A key to the 1 to 2-leaved species of the genus is given, as well as photographs, ecology, and also IUCN conservation status for the new species.

The new species Raphiocarpus axillaris D.J.Middleton from Tam Đảo National Park in northern Vietnam is described and illustrated.