Molecular systematics and biogeography of Crawfurdia, Metagentiana and Tripterospermum (Gentianaceae) based on nuclear ribosomal and plastid DNA sequences.
OBJECTIVE
The systematic position of the genus Metagentiana and its phylogenetic relationships with Crawfurdia, Gentiana and Tripterospermum have not been explicitly addressed. These four genera belong to one of two subtribes (Gentianinae) of Gentianeae. The aim of this paper is to examine the systematic position of Crawfurdia, Metagentiana and Tripterospermum and to clarify their phylogenetic affinities more clearly using ITS and trnL intron sequences.


METHODS
Nucleotide sequences from the internal transcribed spacers (ITS) of nuclear ribosomal DNA and the plastid DNA trnL (UAA) intron were analysed phylogenetically. Ten of fourteen Metagentiana species were sampled, together with 40 species of other genera in the subtribe Gentianinae.


RESULTS
The data support several previously published conclusions relating to the separation of Metagentiana from Gentiana and its closer relationships to Crawfurdia and Tripterospermum based on studies of gross morphology, floral anatomy, chromosomes, palynology, embryology and previous molecular data. The molecular clock hypothesis for the tested sequences in subtribe Gentianinae was not supported by the data (P < 0.05), so the clock-independent non-parametric rate smoothing method was used to estimate divergence time. This indicates that the separation of Crawfurdia, Metagentiana and Tripterospermum from Gentiana occurred about 11.4-21.4 Mya (million years ago), and the current species of these three genera diverged at times ranging from 0.4 to 6.2 Mya.


CONCLUSIONS
The molecular analyses revealed that Crawfurdia, Metagentiana and Tripterospermum do not merit status as three separate genera, because sampled species of Crawfurdia and Tripterospermum are embedded within Metagentiana. The speciation and rapid radiation of these three genera is likely to have occurred in western China as a result of upthrust of the Himalayas during the late Miocene and the Pleistocene.
Chen
Shengyun
S
Laboratory of Qinghai-Tibet Biological Evolution and Adaptation, Northwest Plateau Institute of Biology, Chinese Academy of Sciences, Xining 810001, PR China.
Xia
Tao
T
Wang
Yujin
Y
Liu
Jianquan
J
Chen
Shilong
S
D018744:DNA, Plant / Q000235:genetics*; D004275:DNA, Ribosomal; D003710:Demography; D019143:Evolution, Molecular; D029965:Gentianaceae / Q000145:classification* / Q000235:genetics*; D010802:Phylogeny; D018087:Plastids; D013045:Species Specificity
D018744:DNA, Plant; D004275:DNA, Ribosomal