Evolution of plastid genomes of Holcoglossum (Orchidaceae) with recent radiation.

BACKGROUND: The plastid is a semiautonomous organelle with its own genome. Plastid genomes have been widely used as models for studying phylogeny, speciation and adaptive evolution. However, most studies focus on comparisons of plastid genome evolution at high taxonomic levels, and comparative studies of the process of plastome evolution at the infrageneric or intraspecific level remain elusive. Holcoglossum is a small genus of Orchidaceae, consisting of approximately 20 species of recent radiation. This made it an ideal group to explore the plastome mutation mode at the infrageneric or intraspecific level. RESULTS: In this paper, we reported 15 complete plastid genomes from 12 species of Holcoglossum and 1 species of Vanda. The plastid genomes of Holcoglossum have a total length range between 145 kb and 148 kb, encoding a set of 102 genes. The whole set of ndh-gene families in Holcoglossum have been truncated or pseudogenized. Hairpin inversion in the coding region of the plastid gene ycf2 has been found. CONCLUSIONS: Using a comprehensive comparative plastome analysis, we found that all the indels between different individuals of the same species resulted from the copy number variation of the short repeat sequence, which may be caused by replication slippage. Annotation of tandem repeats shows that the variation introduced by tandem repeats is widespread in plastid genomes. The hairpin inversion found in the plastid gene ycf2 occurred randomly in the Orchidaceae.

Begonia medogensis, a new species of Begoniaceae from Western China and Northern Myanmar.

Begonia medogensis JianW.Li, Y.H.Tan & X.H.Jin, a new species of Begoniaceae, is described and illustrated by colour photographs. Begonia medogensis is distributed in western China and northern Myanmar. It has erect stems, is tuberless, has many triangular to lanceolate leaves, base slightly asymmetric, margins remotely and irregularly denticulate; staminate flowers have 4 perianth segments, with outer 2 segments broadly ovate, inner 2 spathulate; pistillate flowers have 5 perianth segments, unequal, outer 4 broadly ovate, inner 1 spathulate. The new species is assigned to section Platycentrum and can easily be distinguished from the other species in the section.