The occurrence of epidermal crystals in the species of the genus Acalypha (Euphorbiaceae, Acalyphoideae) is described and analyzed. The epidermal surface of 190 Acalypha specimens, belonging to 110 species and subspecies, was studied with a scanning electron microscope (SEM), and the elemental composition of the found crystals was examined using energy-dispersive X-ray spectroscopy (EDS). The results show that 96.4 % of the studied species have epidermal crystals, mainly located on the leaf surface, but also on the bracts and flowers. The crystals exhibit significant variation, and four types of crystals are recognized: prismatic, styloids, stellate, and druses, which are, respectively, designated with Ac, Bc, Cc and Dc letters. We have not found any reference to stellate crystals in the angiosperm morphological or anatomical literature, and druses are observed and described under SEM in Acalypha for the first time. The elemental composition of the crystals shows that all of them exhibit typical peaks of calcium. We discuss the possible taxonomic importance of crystals, due to the association that some of these types of crystals have with groups of closely morphologically related species. We have not found a relation between the presence or the type of crystals and the habitat or distribution of the species that present them. We do not know other genera of Euphorbiaceae where the presence of crystals is so widespread, so we propose that they should be considered as a distinctive feature of this genus.

中文翻译：

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Acalypha（大戟科，Acalyphoideae）中的表皮晶体作为该属的新分类特征

描述和分析了 Acalypha 属（大戟科，Acalyphoideae）中表皮晶体的出现。用扫描电子显微镜 (SEM) 研究了属于 110 个物种和亚种的 190 个 Acalypha 标本的表皮表面，并使用能量色散 X 射线光谱 (EDS) 检查发现的晶体的元素组成。结果表明，96.4%的研究物种具有表皮晶体，主要分布在叶面，但也分布在苞片和花上。晶体表现出显着的变异，可识别出四种类型的晶体：棱柱状、茎状体、星状晶体和晶簇状晶体，分别用 Ac、Bc、Cc 和 Dc 字母表示。我们在被子植物形态学或解剖学文献中没有发现任何对星状晶体的引用，首次在 Acalypha 中在 SEM 下观察和描述了花蕊。晶体的元素组成表明它们都表现出典型的钙峰。我们讨论了晶体可能在分类学上的重要性，因为这些类型的晶体中的一些与形态上密切相关的物种群有关联。我们还没有发现晶体的存在或类型与呈现它们的物种的栖息地或分布之间的关系。我们不知道大戟科的其他属中晶体的存在如此广泛，因此我们建议将它们视为该属的一个显着特征。我们讨论了晶体可能在分类学上的重要性，因为这些类型的晶体中的一些与形态上密切相关的物种群有关联。我们还没有发现晶体的存在或类型与呈现它们的物种的栖息地或分布之间的关系。我们不知道大戟科的其他属中晶体的存在如此广泛，因此我们建议将它们视为该属的一个显着特征。我们讨论了晶体可能在分类学上的重要性，因为这些类型的晶体中的一些与形态上密切相关的物种组有关联。我们还没有发现晶体的存在或类型与呈现它们的物种的栖息地或分布之间的关系。我们不知道大戟科的其他属中晶体的存在如此广泛，因此我们建议将它们视为该属的一个显着特征。