Phenotypic plasticity is common in aquatic monocots, but is sometimes mistaken with heteroblasty. In Eriocaulaceae, aquatic and amphibious species may present interesting adaptive morphological features. However, Paepalanthus saxicola var. pilosus is unusual by having two leaf morphotypes and scapes that can be partially submerged or completely exposed. This taxon also presents an uncertain identity due to its incomplete morphological description. Here, we studied the morphology and anatomy of both leaf morphotypes and of scapes of P. saxicola var. pilosus to understand if the morphological differences in leaves correspond to phenotypic plasticity or heteroblasty; and the ecological and systematic significance of its leaves and scapes. Besides, we describe its morphology to evaluate its identity. The short curved leaves show supporting tissue and three vascular bundles, while the long filiform ones lack supporting tissue and have a single vascular bundle. All specimens share anatomical characteristics of scape. We raised this taxon to the species level, giving it a replacing name, Paepalanthus amphibius. We observed that P. amphibius is the first confirmed report of heterophylly in Eriocaulaceae. The anatomy of its short leaves and scapes reflects adaptations to a xeric environment, while the anatomy of the long leaves shows characteristics adapted to an aquatic habit. Possibly, such degree of plasticity is underreported in the family, so we stress the importance of seasonal studies to understand the morphology and taxonomy of the amphibious species.

表型可塑性在水生单子叶植物中很常见，但有时会误认为是异源性。在鸢尾科，水生和两栖物种可能会表现出有趣的适应性形态特征。但是，Paepalanthus saxicola var。毛虫具有两种叶片形态和花序，可以部分浸没或完全暴露，因此是不寻常的。由于其形态描述不完整，该分类单元也呈现出不确定的身份。在这里，我们研究了P. saxicola var叶片形态和花scape的形态和解剖结构。皮洛苏斯了解叶片的形态差异是否对应于表型可塑性或异胚性；以及其叶子和花的生态和系统意义。此外，我们描述其形态来评估其身份。弯曲的短叶显示出支持组织和三个维管束，而长丝状的叶片缺乏支持组织并具有单个维管束。所有标本都具有花的解剖特征。我们将此分类单元提高到物种级别，并为其取了一个替代名称Paepalanthus amphibius。我们观察到两栖对虾是首次在鸢尾科中证实了杂种。它的短叶和花的解剖结构反映了对干燥环境的适应，而长叶的解剖图则显示了适应水生习性的特征。可能这样的可塑性程度在家庭中被低估，因此我们强调季节性研究对了解两栖动物的形态和分类学的重要性。