Desmidiales (Desmidiaceae, Zygnematophyceae) from lowland rivers and floodplain lakes of Ecuadorian Amazonia

We present the results of a taxonomic survey of desmidiales (Desmidiaceae Ralfs, Zygnematophyceae Round ex Guiry) in floodplain lakes and tributaries of the Napo-Aguarico River in the Ecuadorian Amazon. Surface water samples were collected for taxonomic analysis at each site during two different hydrological periods in 2021 and 2022. Our sites share a typical blackwater typology, with high water transparency, low conductivity, acidic, and soft waters. In this study we documented 42 specific or infraspecific taxa in 10 genera within the Desmidiaceae family: Bambusina Kützing ex Kützing (1), Cosmarium Corda ex Ralfs (9), Desmidium C.Agardh ex Ralfs (3), Euastrum Ehrenberg ex Ralfs (3), Hyalotheca Ehrenberg ex Ralfs (2), Micrasterias C.Agardh ex Ralfs (12), Pleurotaenium Nägeli (2), Staurastrum Meyen ex Ralfs (6), Staurodesmus Teiling (2), and Xanthidium Ehrenberg ex Ralfs (2). From those taxa, 15 are new records to the lowlands of western Amazonia, and three of them (Cosmarium quadriverrucosum var. supraornatum Skuja, Micrasterias fimbriata var. spinosa Bisset, and Micrasterias furcata var. dichotoma (Wolle) Růžička) to the Amazon Basin. The number of species recorded at various sites differed greatly. We found 28 taxa for the Lagartococha River and 27 for Delfincocha Lake. For the remaining sites, we observed only two to nine species, which may be related to the presence or absence of aquatic macrophytes. All taxa were recorded during 2022, but only 20 out of 42 were observed in 2021. This variation is likely due to the hydrological regime, as it occurs in other Neotropical floodplains. Our findings underscore the importance of conducting additional phycological studies in these largely unexplored ecosystems, which are in peril owing to oil extraction activities in the western region of the Amazon Basin.