Fifty years ago, the enigmatic Brazilian myxomycete-species Didymium aquatile was described and analyzed with respect to the structure of the plasmodium and its spores. In this study, we compare this rare plasmodial slime mold with another, temporarily aquatic taxon from Europe, Didymium nigripes. Phenotypic plasticity of D. nigripes was investigated under various environmental conditions. Large changes in the morphology of the plasmodia were observed. For species identification, characteristics of the fruiting bodies are key features. However, Didymium aquatile was only characterized by its “abnormal” plasmodia, but no molecular data were available. Here, we analyzed DNA-sequences of 22 species of the genera Didymium and Diderma with a focus on this South American taxon via molecular genetics. A comparison of 18S-rDNA-sequences from D. aquatile and 21 other Didymium (and Diderma)-species indicates that D. aquatile is a reproductively isolated morpho-species. Phenotypic plasticity of D. nigripes is documented with respect to plasmodium morphology and the formation of fruiting bodies, as an example of an adaptation of a terrestrial species to aquatic environments.

五十年前，人们描述并分析了神秘的巴西粘菌菌种水生镨的疟原虫及其孢子的结构。在这项研究中，我们将这种罕见的疟原虫粘菌与来自欧洲的另一种暂时水生分类群黑镨镨进行了比较。在不同环境条件下研究了D. nigripes的表型可塑性。观察到疟原虫形态的巨大变化。对于物种鉴定，子实体的特征是关键特征。然而，水生镨的特征仅在于其“异常”的疟原虫，但没有可用的分子数据。在这里，我们通过分子遗传学分析了Didymium属和Diderma属 22 个物种的 DNA 序列，重点关注这一南美分类单元。水生D.  aquatile和其他 21 个Didymium（和Diderma）物种的 18S-rDNA 序列的比较表明， D.  aquatile是一种生殖隔离的形态物种。记录了D. nigripes在疟原虫形态和子实体形成方面的表型可塑性，作为陆生物种适应水生环境的一个例子。