豆科长柄山蚂蝗属的分子系统学研究

The genus Hylodesmum comprises about 13 species of the family Leguminosae and it is disjunctively distributed in eastern Asia and eastern North America, with the center of distribution in China. The morphological studies have suggested that the genus Hylodesmum as currently circumscribed may be an unnatural group for the following four reasons: 1) Hylodesmum menglaense was transferred into the genus Verdesmum as V. menglaense based on the fruit characters, but the features of the inflorescence and flowers support it is kept in Hylodesmum; 2) It is long controversial in the generic affiliation of Hylodesmum sect. Repanda: some authors kept it in the genus Hylodesmum, while others placed it in the genus Desmodium; 3) Three species of the genus Desmodium (D. vidalii, D. axillare, and D. wydlerianum) share many important features with Hylodesmum, especially in the fruit characters, and thus they may be transferred into the latter; 4) Hylodesmum has an unclear relationship with Monarthrocarpus and Verdesmum due to the overlap in morphological characters. Additionally, within the genus Hylodesmum, the phylogenetic relationship between eastern Asian and eastern North American species remains unclear. In this study, we will perform a comprehensive molecular analysis based on extensive sampling of Hylodesmum and the related genera using eight DNA regions (ITS, ETS, trnK/matK, rbcL, trnL-F, rpl16, rpl32-trnL, and trnH-psbA), to test the monophyly of Hylodesmum, to evaluate its phylogenetic relationships with the related genera, and to construct their biogeographical diversification history. The completion of this project may throw light on the temporal and spatial evolutionary processes of the disjunction between eastern Asia and eastern North America, and will be as a part of our endeavor for the molecular systematic study of the polyphyletic genus Desmodium.

长柄山蚂蝗属是豆科中一个间断分布于东亚与北美东部的小属，约13种，我国是其分布中心。形态学研究表明：(1)目前界定的长柄山蚂蝗属可能不是一个单系类群，对于勐腊长柄山蚂蝗是否应该从该属中转移出去、长萼齿组是否应该保留在该属中、山蚂蝗属的3个种是否应该被纳入该属，以及该属与春带豆属、单节豆属之间的系统学关系如何，亟需分子系统学上的证据；(2)长柄山蚂蝗属的北美种与东亚种的系统学关系也不确定。本项目拟利用2个nrDNA片段和6个cpDNA片段，重建长柄山蚂蝗属及其近缘属的系统发育，据以验证属的单系性，评价属间关系，从而明确长柄山蚂蝗属的范围，解决北美种与东亚种的系统学关系。在重建的系统发育基础上，利用豆科丰富的化石记录，估算该属的分化时间，揭示其生物地理分化历史，并进一步探讨该属在东亚与北美东部间断分布格局的形成机制。本项目的开展，也能为近缘的山蚂蝗属的分子系统学研究奠定良好的工作基础。

长柄山蚂蝗属是豆科中一个间断分布于东亚与北美东部的小属，全世界13种4亚种，我国有10种4亚种，是该属的分布中心。本项目经过3年，(1)野外调查了全部13种4亚种，尤其仔细观察了每种的花和果实形态；(2)查阅国内外标本馆1万余份标本，发现我国特有的2种植物(浅波叶长柄山蚂蝗和云南长柄山蚂蝗)在邻近国家也有分布；(3)基于形态和分子系统学证据，将勐腊长柄山蚂蝗从春带豆属重新转入长柄山蚂蝗；(4)对全部13种4亚种共37个样品进行分子测序获得了完整叶绿体基因组数据，以此构建了高支持率的系统发育树，确认长柄山蚂蝗属为单系类群，发现传统定义的长萼齿组是并系因而需要重新定义，北美3个种属于不同的3个分支因而不是单次起源，疏花长柄山蚂蝗、长柄山蚂蝗、及尖叶长柄山蚂蝗均非单系类群。本项目的执行，使得长柄山蚂蝗属的大多数分类学和系统学问题得到较好地解决，同时也加深了对东亚与北美东部间断分布的时空进化过程的理解。