Schmidt Sabrina A, Schmiedel Ute, Carstens Frederic, Rau Anna-Lena, Rudolph-Bartsch Barbara
Institute of Plant Science and Microbiology, University of Hamburg, Hamburg, Germany.
Centre of Methods, Leuphana University Lüneburg, Lüneburg, Germany.
Ann Bot. 2025 Mar 13;135(4):735-756. doi: 10.1093/aob/mcae207.
Oophytum (Aizoaceae) is a locally endemic genus of the extremely fast-evolving subfamily Ruschioideae and consists of only two formally accepted species (Oophytum nanum and Oophytum oviforme). Both species are leaf-succulent dwarf shrubs and habitat specialists on quartz fields in the Knersvlakte, a renowned biodiversity hotspot in the arid winter-rainfall Succulent Karoo Biome of South Africa. Quartz fields present specialised patchy habitats with an island-like distribution in the landscape. Oophytum oviforme grows in the south-western part, whereas O. nanum covers most of the remaining Knersvlakte. These species co-occur in a small area, but within different quartz islands. We investigated the effects of the patchy distribution, environmental conditions and potential effects of palaeoclimatic changes on the genetics of Oophytum.
Phylogenetic and population genetic analyses of 35 populations of the genus, covering its entire distribution area, were conducted using four chloroplast DNA markers and an amplified fragment length polymorphism dataset. These were combined with environmental data via a principal component analysis and comparative heatmap analyses.
The genetic pattern of the Oophytum metapopulation is a tripartite division, with northern, central and western groups. This geographical pattern does not correspond to the two-species concept of Oophytum. Only the western O. oviforme populations form a monophyletic lineage, whereas the central populations of O. oviforme are genetic hybrids of O. nanum populations. The highly restricted gene flow often resulted in private gene pools with very low genetic diversity, in contrast to the hybrid gene pools of the central and edge populations.
Oophytum is an exceptional example of an extremely fast-evolving genus that illustrates the high speciation rate of the Ruschioideae and their success as one of the leading plant groups of the drought-prone Succulent Karoo Biome. The survival strategy of these dwarf quartz-field endemics is an interplay of adaptation to diverse island habitats, highly restricted gene flow, occasional long-distance dispersal, migration, founder effects and hybridisation events within a small and restricted area caused by glacial and interglacial changing climate conditions from the Pleistocene to the Present. These findings have important implications for future conservation management strategies.
卵叶花属（番杏科）是快速演化的露子花亚科中的一个地方特有属，仅包含两个正式认可的物种（卵叶花和卵形卵叶花）。这两个物种均为叶肉质矮灌木，是南非干旱冬雨型多肉植物卡鲁生物群落中著名的生物多样性热点地区克尼斯纳夫特石英地的栖息地特化物种。石英地呈现出特殊的斑块状栖息地，在景观中呈岛状分布。卵形卵叶花生长在西南部地区，而卵叶花覆盖了克尼斯纳夫特其余大部分地区。这两个物种在一个小区域内共存，但分布在不同的石英岛中。我们研究了斑块状分布、环境条件以及古气候变化对卵叶花属遗传学的潜在影响。
利用四个叶绿体DNA标记和一个扩增片段长度多态性数据集，对该属涵盖其整个分布区域的35个种群进行了系统发育和种群遗传学分析。通过主成分分析和比较热图分析将这些数据与环境数据相结合。
卵叶花复合种群的遗传模式呈三分法，分为北部、中部和西部群体。这种地理模式与卵叶花属的两物种概念不相符。只有西部的卵形卵叶花种群形成一个单系谱系，而卵形卵叶花的中部种群是卵叶花种群的遗传杂交种。与中部和边缘种群的杂交基因库相比，高度受限的基因流常常导致具有极低遗传多样性的特有基因库。
卵叶花属是快速演化属的一个特殊例子，说明了露子花亚科的高物种形成率以及它们作为干旱多发的多肉植物卡鲁生物群落中主要植物类群之一的成功。这些矮生石英地特有物种的生存策略是在一个小而受限的区域内，通过适应多样的岛屿栖息地、高度受限的基因流、偶尔的长距离扩散、迁移、奠基者效应以及由更新世至今的冰川和间冰期气候变化导致的杂交事件之间的相互作用。这些发现对未来的保护管理策略具有重要意义。
