Plastome structure, phylogeny and evolution of plastid genes in Reevesia (Helicteroideae, Malvaceae).

Reevesia is an eastern Asian-eastern North American disjunction genus in the family Malvaceae s.l. and comprises approximately 25 species. The relationships within the genus are not well understood. Here, 15 plastomes representing 12 Reevesia species were compared, with the aim of better understanding the species circumscription and phylogenetic relationships within the genus and among genera in the family Malvaceae s.l. The 11 newly sequenced plastomes range between 161,532 and 161, 945 bp in length. The genomes contain 114 unique genes, 18 of which are duplicated in the inverted repeats (IRs). Gene content of these plastomes is nearly identical. All the protein-coding genes are under purifying selection in the Reevesia plastomes compared. The top ten hypervariable regions, SSRs, and the long repeats identified are potential molecular markers for future population genetic and phylogenetic studies. Phylogenetic analysis based on the whole plastomes confirmed the monophyly of Reevesia and a close relationship with Durio (traditional Bombacaceae) in subfamily Helicteroideae, but not with the morphologically similar genera Pterospermum and Sterculia (both of traditional Sterculiaceae). Phylogenetic relationships within Reevesia suggested that two species, R. pubescens and R. thyrsoidea, as newly defined, are not monophyletic. Six taxa, R. membranacea, R. xuefengensis, R. botingensis, R. lofouensis, R. longipetiolata and R. pycnantha, are suggested to be recognized.

Resurrection of Sorbustapashana (Rosaceae) based on molecular and morphological evidence.

Sorbustapashana (Rosaceae) from Taibai Shan, Qinling, China, has been treated as a synonym of S.tianschanica. Both species belong to a distinctive group characterized by white tomentose buds, relatively large flowers, and red fruits. However, these two species do not cluster together in the plastome-based phylogenetic analysis. Morphologically, S.tapashana differs from S.tianschanica by its persistent white tomentose on the peduncle, pedicels, rachis, both sides of the midrib on abaxial surface, its leaflets with 31-51 teeth on each side and much smaller corymbs and fruits. Therefore, S.tapashana is reinstated as a distinct species here.