New Neidium (Neidiaceae: Bacillariophyta) Pfitzer species from a clear water lake in the Brazilian Amazon (Santarém, Pará, Brazil)

Two new species of Neidium, Neidium saire and Neidium mocorongo, are described from Verde Lake, located in the lower central region of the Amazon Basin, Brazil. Verde Lake is a clear water lake characterized by low pH (5.5–5.9), low conductivity (5.4–7.6 µS cm-1), and shallow Secchi depth (0.8–1.45 m). The lake has poorly buffered waters with seasonal algal blooms, driven by natural and anthropogenic disturbances. The new species contributes to a diverse flora of unique species from the Amazon region. Currently, more than 25 Neidium taxa are recognized in the Amazon, comparable to species numbers in other parts of South America and North America. In this study, similarities in valve morphologies between the North American species and Amazonian species of Neidium are considered, suggesting possible similarities in morphological development between continents.