Abstract Succulence is widely interpreted as an adaptation to drought, usually associated with CAM and xeromorphic features among arid-adapted plants. However, this syndrome can also be observed in species typical of mesic and even hydric environments. The leaf-succulent genus Crassula (Crassulaceae) occurs in contrasting habitats in all nine biomes of southern Africa. This study represents the first to compare leaf traits in Crassula species which in nature are confined to diverse habitats in southern Africa. To determine their potential adaptive significance, we investigated leaf succulence and several morpho-anatomical traits of five southern African Crassula species (C. ausensis, C. brevifolia, C. multicava, C. nudicaulis, C. tecta), which occur naturally in habitats of differing aridity; all plants were grown under glasshouse conditions. For each species, we recorded water content, leaf anatomy, and leaf surface structure and hydrophobicity. We found that water content is relatively consistent in Crassula regardless of natural habitat. In contrast, most leaf morpho-anatomical traits examined here are related to macroclimatic conditions. We hypothesize that differences in mesophyll traits in Crassula are potentially linked to water storage and CAM performance, while differences in leaf surface properties are more closely related to water conservation and probably also to water uptake through hydathodes.

中文翻译：

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干旱栖息地的进化成功：南部非洲景天属植物多汁叶片的形态解剖学

摘要 多肉植物被广泛解释为对干旱的适应，通常与适应干旱的植物的 CAM 和异形特征有关。然而，这种综合征也可以在典型的中等甚至氢环境的物种中观察到。叶肉质植物景天属（景天科）出现在非洲南部所有九个生物群落的对比生境中。这项研究首次比较了景天属植物的叶子特征，景天属植物在自然界中仅限于南部非洲的不同栖息地。为了确定它们的潜在适应性意义，我们调查了五种南部非洲景天属植物（C. ausensis、C. brevifolia、C. multicava、C. nudicaulis、C. tecta）的叶肉质和几种形态解剖特征，它们在栖息地中自然发生不同的干旱；所有植物都在温室条件下生长。对于每个物种，我们记录了含水量、叶片解剖结构、叶片表面结构和疏水性。我们发现无论自然栖息地如何，景天树的含水量相对一致。相比之下，这里检查的大多数叶片形态解剖特征与大气候条件有关。我们假设景天树中叶肉性状的差异可能与储水和 CAM 性能有关，而叶表面特性的差异与节水更密切相关，也可能与通过水源吸收的水分有关。这里检查的大多数叶片形态解剖特征与大气候条件有关。我们假设景天树中叶肉性状的差异可能与储水和 CAM 性能有关，而叶表面特性的差异与节水更密切相关，也可能与通过水源吸收的水分有关。这里检查的大多数叶片形态解剖特征与大气候条件有关。我们假设景天树中叶肉性状的差异可能与储水和 CAM 性能有关，而叶表面特性的差异与节水更密切相关，也可能与通过水源吸收的水分有关。