Department of Systematic Botany, Justus-Liebig-University, Giessen, Germany.
Plant Biol (Stuttg). 2011 Mar;13(2):368-80. doi: 10.1111/j.1438-8677.2010.00354.x.
Southern Africa is one of the hot spots for plant biodiversity, with ca. 80% of species endemic to this area. Rapid and recent radiations in Southern African plant genera were triggered by fine-scale differences in climate, topography and geology. The genus Lithops (Ruschioideae, Aizoaceae) contains 37 species and is widely distributed in Southern Africa. Species delimitation within the genus is challenging because the limited number of morphological characters in these reduced succulents varies intensely between populations, presumably as adaptations to local geological environments. We analysed phylogenetic relationships within Lithops using non-coding chloroplast DNA (trnS-trnG intergenic spacer), nuclear ribosomal internal transcribed spacer (nrITS) sequences and AFLP data. Genetic variability of the sequence data was very low, but AFLP data detected nine clades within Lithops that do not fit current morphology-based taxonomy. Two of these clades are separated by their distribution on the northern and eastern border of the distribution area, and four clades are found in the Gariep Centre in the estuary of the Orange River. Morphological similarities, especially colour of leaves, evolved repeatedly within the clades, thus we hypothesise that closely related species became adapted to different soil types in a mosaic-like geological environment. One-third of the species are found in the Gariep Centre, characterised by extremely diverse edaphic habitats.
南非是植物生物多样性的热点地区之一，约有 80%的物种为该地区特有。南非植物属的快速和近期辐射是由气候、地形和地质的细微差异引发的。生石花属（Ruschioideae，番杏科）包含 37 个物种，广泛分布于南非。由于这些简化的肉质植物的形态特征数量有限，在种群之间变化剧烈，可能是对当地地质环境的适应，因此该属内的物种划分具有挑战性。我们使用非编码叶绿体 DNA（trnS-trnG 基因间隔区）、核核糖体内部转录间隔区（nrITS）序列和 AFLP 数据分析了生石花属内的系统发育关系。序列数据的遗传变异非常低，但 AFLP 数据检测到生石花属内有九个不适合当前基于形态的分类的类群。其中两个类群分布在分布区的北部和东部边界，四个类群分布在奥兰治河河口的加里卜中心。类群内的形态相似性，特别是叶子的颜色，多次进化，因此我们假设密切相关的物种适应了马赛克状地质环境中的不同土壤类型。三分之一的物种分布在加里卜中心，其特点是土壤类型极其多样化。
