This study focused on the genus Phacus Duj. of "Lago da Ponte," located in the Jardim Botânico of Porto Alegre, Rio Grande do Sul (30°03'05"S and 51°10'34"W). The study of "Lago da Ponte" aimed to identify Phacus species from 24 samples collected monthly (from July/2007 to June/2008) using a plankton net along two margins of the lake. Other goals of this study were to compare the richness of this genus in this environment because it was transformed from a swamp to a lake, and to supply with the amplitude of the environmental variable of occurrence of each taxon. Based on the qualitative analysis, 22 specific and infra-specific taxa were recorded. These were distributed in 18 typical varieties, three varieties that were not typical of the species, and one in a form that was not typical. Phacus brachykentron Pochm. and P. stokesii Lemm. are cited for the first time for Rio Grande do Sul. The most frequent taxa were the following: Phacus brachykentron Pochm., P. longicauda (Ehr.) Duj., P. hamatus Pochm, P. orbicularis Hübner and P. raciborskii Drez.var. longus Conf. The comparison of richness of the swamp versus lake, according to the Sörensen index, indicated low similarity between these aquatic biotopes, with a greater Phacus richness in the lake system.
Euglenophyta; taxonomy of Phacus; distribution; south of Brazil
