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AOBPreview published online on July 1, 2005
Annals of Botany, doi:10.1093/aob/mci188
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© The Author 2005. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oupjournals.org
Received November 25, 2004
Revised March 8, 2005
Accepted May 4, 2005

Article

Molecular Systematics and Biogeography of Crawfurdia, Metagentiana and Tripterospermum (Gentianaceae) Based on Nuclear Ribosomal and Plastid DNA Sequences

SHENGYUN CHEN 1, TAO XIA 1, YUJIN WANG 1, JIANQUAN LIU 2, and SHILONG CHEN 2*

1 Laboratory of Qinghai-Tibet Biological Evolution and Adaptation, Northwest Plateau Institute of Biology, Chinese Academy of Sciences, Xining 810001, P. R. China; Graduate School of the Chinese Academy of Sciences, Beijing 100039, China
2 Laboratory of Qinghai-Tibet Biological Evolution and Adaptation, Northwest Plateau Institute of Biology, Chinese Academy of Sciences, Xining 810001, P. R. China

* To whom correspondence should be addressed.
SHILONG CHEN, E-mail: chenshil{at}public.xn.qh.cn


  Abstract

• Background and Aims 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.

• Key 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 11·4-21·4Mya (million years ago), and the current species of these three genera diverged at times ranging from 0·4 to 6·2Mya.

• 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.

Keywords: Asia, biogeography, Crawfurdia, Gentiana, Gentianeae, Gentianaceae, Metagentiana, molecular systematics, ITS, trnL (UAA) intron, Tripterospermum.
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