Ellison Nick W, Liston Aaron, Steiner Jeffrey J, Williams Warren M, Taylor Norman L
Grasslands Research Centre, AgResearch, Private Bag 11008, Palmerston North, New Zealand.
Mol Phylogenet Evol. 2006 Jun;39(3):688-705. doi: 10.1016/j.ympev.2006.01.004. Epub 2006 Feb 17.
Trifolium, the clover genus, is one of the largest genera of the legume family. We conducted parsimony and Bayesian phylogenetic analyses based on nuclear ribosomal DNA internal transcribed spacer and chloroplast trnL intron sequences obtained from 218 of the ca. 255 species of Trifolium, representatives from 11 genera of the vicioid clade, and an outgroup Lotus. We confirm the monophyly of Trifolium, and propose a new infrageneric classification of the genus based on the phylogenetic results. Incongruence between the nrDNA and cpDNA results suggests five to six cases of apparent hybrid speciation, and identifies the putative progenitors of the allopolyploids T. dubium, a widespread weed, and T. repens, the most commonly cultivated clover species. Character state reconstructions confirm 2n=16 as the ancestral chromosome number in Trifolium, and infer a minimum of 19 instances of aneuploidy and 22 of polyploidy in the genus. The ancestral life history is hypothesized to be annual in subgenus Chronosemium and equivocal in subgenus Trifolium. Transitions between the annual and perennial habit are common. Our results are consistent with a Mediterranean origin of the genus, probably in the Early Miocene. A single origin of all North and South American species is hypothesized, while the species of sub-Saharan Africa may originate from three separate dispersal events.
三叶草属（Trifolium）是豆科中最大的属之一。我们基于核糖体DNA内部转录间隔区以及叶绿体trnL内含子序列，对约255种三叶草中的218种、蚕豆状分支11个属的代表植物以及外类群百脉根属（Lotus）进行了简约法和贝叶斯系统发育分析。我们确认了三叶草属的单系性，并根据系统发育结果提出了该属新的属下分类。核核糖体DNA（nrDNA）和叶绿体DNA（cpDNA）结果之间的不一致表明存在五到六个明显的杂交物种形成案例，并确定了广泛分布的杂草——可疑三叶草（T. dubium）和最常种植的三叶草物种——白车轴草（T. repens）这两个异源多倍体的假定亲本。性状状态重建证实2n = 16是三叶草属的祖先染色体数，并推断该属至少有19次非整倍体事件和22次多倍体事件发生。推测祖先的生活史在时间半莲亚属（Chronosemium）中为一年生，在三叶草亚属（Trifolium）中不明确。一年生和多年生习性之间的转变很常见。我们的结果与该属起源于地中海地区、可能是在中新世早期的观点一致。假设所有北美和南美物种都有单一的起源，而撒哈拉以南非洲的物种可能起源于三次独立的扩散事件。
