The periphytic diatoms attached to Polygonum hydropiperoides Michaux were studied with sampling, in the reservoir of the Passaúna river, Paraná State, Brazil. Parts of the macrophyte were scraped to remove the periphytic matrix which was cleaned to make permanent slides. One hundred and six taxa were determined. Fragilariaceae was the most representative family, with eight genera. Navicula Bory, Gomphonema Ehrenberg and Nitzschia Hassall showed the greater species richness among the 39 genera observed. Fifteen taxa are new records to Paraná state.
Diatomeae; lentic environment; epiphyton; taxonomy
