Data from: Insights on the evolution of plant succulence from a remarkable radiation in Madagascar (Euphorbia)

Patterns of adaptation in response to environmental variation are central to our understanding of biodiversity, but predictions of how and when broad scale environmental conditions such as climate affect organismal form and function remain incomplete. Succulent plants have evolved in response to arid conditions repeatedly, with various plant organs such as leaves, stems, and roots physically modified to increase water storage. Here we investigate the role played by climate conditions in shaping the evolution of succulent forms in a plant clade endemic to Madagascar and the surrounding islands, part of the hyper-diverse genus Euphorbia (Euphorbiaceae). We used multivariate ordination of 19 climate variables to identify links between particular climate variables and three major forms of succulence – succulent leaves, cactiform stem succulence, and tubers. We then tested the relationship between climatic conditions and succulence, using comparative methods that account for shared evolutionary history. We confirm that plant water storage is associated with the two components of aridity, temperature and precipitation. Cactiform stem succulence, however, is not prevalent in the driest environments, countering the widely-held view of cactiforms as desert icons. Instead, leaf succulence and tubers are significantly associated with the lowest levels of precipitation. Our findings provide a clear link between broad scale climatic conditions and local adaptation in land plants, and new insights into the climatic conditions favoring different forms of succulence. This evidence for adaptation to climate raises concern over the evolutionary future of succulent plants as they, along with other organisms, face anthropogenic climate change.生物应对环境变化的适应模式，是解析生物多样性的核心研究主题，但针对气候等大范围环境条件如何、何时影响生物体形态与功能的预测，仍有待完善。多肉植物（succulent plants）多次独立演化以适应干旱环境，其叶、茎、根等多种器官发生形态特化，以提升储水能力。本研究以隶属于大戟科（Euphorbiaceae）超多样大戟属（Euphorbia）的马达加斯加及周边群岛特有植物支系为研究对象，探讨气候条件在其肉质形态演化过程中所发挥的作用。我们通过对19个气候变量开展多元排序分析，识别出特定气候变量与三类主要肉质性状——叶肉质化、仙人掌状茎肉质化以及块茎之间的关联。随后，我们采用考虑共同演化历史的比较分析方法，检验了气候条件与肉质性状之间的关联。本研究证实，植物储水能力与干旱的两个核心要素——温度与降水密切相关。但仙人掌状茎肉质化并未在最干旱的环境中最为普遍，这与学界及大众将仙人掌状植物视为沙漠标志性物种的普遍认知相悖。与之相反，叶肉质化与块茎性状显著关联于降水水平最低的生境。本研究结果明确了大范围气候条件与陆地植物局部适应之间的直接关联，同时为解析青睐不同肉质形态的气候条件提供了全新视角。由于多肉植物与其他生物一样，正面临人为引发的气候变化，本研究中关于气候适应的相关发现，也为多肉植物的演化前景敲响了警钟。