Several strains of terrestrial algae isolated from biological soil crusts in Germany and Ukraine were identified by morphological methods as the widely distributed species Dictyosphaerium minutum (=Dictyosphaerium chlorelloides). Investigation of the phylogeny showed their position unexpectedly outside of Chlorellaceae (Trebouxiophyceae) and distantly from Chlorella chlorelloides, to which this taxon was attributed after revision of the genus Chlorella based on an integrative approach. SSU rRNA phylogeny determined the position of our strains inside a clade recently described as a new genus of the cryptic alga Xerochlorella olmiae isolated from desert biological soil crusts in the United States. Investigation of the morphology of the authentic strain of X. olmiae showed Dictyosphaerium‐like morphology, as well as some other characters, common for our strains and morphospecies D. minutum. The latter alga was described as terrestrial and subsequently united with the earlier described aquatic representative D. chlorelloides because of their similar morphology. The revision of Chlorella mentioned above provided only one aquatic strain (D. chlorelloides), which determined its position in the genus. But terrestrial strains of the morphospecies were not investigated phylogenetically. Our study showed that the terrestrial D. minutum is not related to the morphologically similar D. chlorelloides (=Chlorella chlorelloides, Chlorellaceae), and instead represented a separate lineage in the Trebouxiophyceae, recently described as genus Xerochlorella. Therefore, revision of Xerochlorella is proposed, including nomenclatural combinations, epitypifications, and emendations of two species: X. minuta and X. dichotoma. New characters of the genus based on investigation of morphology and ultrastructure were determined.

中文翻译：

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陆生藻类中的类盘藻形态：什么是小球藻（Trebouxiophyceae，Chlorophyta）？ 1．

从德国和乌克兰的生物土壤结皮中分离出的几种陆生藻类通过形态学方法被鉴定为广泛分布的物种Dictyosphaerium minutum (= Dictyosphaerium chlorelloides )。对系统发育的调查显示它们的位置出乎意料地在小球藻科（Trebouxiophyceae）之外并且远离小球藻（Chlorella chlorelloides），这是在基于综合方法对小球藻属进行修订后归因于该分类群。SSU rRNA 系统发育确定了我们的菌株在进化枝中的位置，该进化枝最近被描述为神秘藻类Xerochlorella olmiae的新属从美国沙漠生物土壤结皮中分离出来。对真正的X. olmiae菌株形态的调查显示，类似于Dictyosphaerium的形态，以及我们的菌株和形态种D. minutum常见的一些其他特征。后一种藻类被描述为陆生藻类，随后与早期描述的水生代表D. chlorelloides结合在一起，因为它们的形态相似。上述小球藻的修订只提供了一种水生菌株（D. chlorelloides)，这决定了它在该属中的位置。但是没有对形态物种的陆生菌株进行系统发育研究。我们的研究表明，陆生D. minutum与形态相似的D. chlorelloides（= Chlorella chlorelloides , Chlorellaceae）无关，而是代表了最近被描述为小球藻属的 Trebouxiophyceae 中的一个独立谱系。因此，提议对小球藻进行修订，包括命名组合、表型和两个物种的修正：X. minuta和X. dichotoma。基于形态学和超微结构的研究确定了该属的新性状。