The Morton Arboretum, 4100 Illinois Route 53, Lisle, IL 60532-1293, USA.
Mol Phylogenet Evol. 2012 Jun;63(3):650-5. doi: 10.1016/j.ympev.2012.02.005. Epub 2012 Feb 19.
The sedge family (Cyperaceae: Poales; ca. 5600 spp.) is a hyperdiverse cosmopolitan group with centres of species diversity in Africa, Australia, eastern Asia, North America, and the Neotropics. Carex, with ca. 40% of the species in the family, is one of the most species-rich angiosperm genera and the most diverse in temperate regions of the Northern Hemisphere, making it atypical among plants in that it inverts the latitudinal gradient of species richness. Moreover, Carex exhibits high rates of chromosome rearrangement via fission, fusion, and translocation, which distinguishes it from the rest of the Cyperaceae. Here, we use a phylogenetic framework to examine how the onset of contemporary temperate climates and the processes of chromosome evolution have influenced the diversification dynamics of Carex. We provide estimates of diversification rates and map chromosome transitions across the evolutionary history of the main four clades of Carex. We demonstrate that Carex underwent a shift in diversification rates sometime between the Late Eocene and the Oligocene, during a global cooling period, which fits with a transition in diploid chromosome number. We suggest that adaptive radiation to novel temperate climates, aided by a shift in the mode of chromosome evolution, may explain the large-scale radiation of Carex and its latitudinal pattern of species richness.
莎草科（莎草目：Cyperaceae；约 5600 种）是一个超多样化的世界性群体，其物种多样性中心位于非洲、澳大利亚、东亚、北美和新热带地区。莎草属（Carex）是该科物种最丰富的属之一，约占该科物种的 40%，在北半球温带地区的物种多样性最为丰富，这使得它在植物中与众不同，因为它反转了物种丰富度的纬度梯度。此外，莎草属通过分裂、融合和易位发生染色体重排的速度非常快，这使其与莎草科的其他属区别开来。在这里，我们使用系统发育框架来研究当代温带气候的出现和染色体进化过程如何影响莎草属的多样化动态。我们提供了多样化率的估计值，并绘制了主要的四个莎草属分支的进化历史上的染色体转变图。我们表明，莎草属的多样化率在渐新世到上新世之间的某个时候发生了变化，这与二倍体染色体数目的转变相吻合。我们认为，对新型温带气候的适应性辐射，加上染色体进化模式的转变，可能解释了莎草属的大规模辐射及其物种丰富度的纬度模式。
