The objective of this study was to evaluate the taxonomic composition and richness of the genera Trachelomonas and Strombomonas (pigmented Euglenophyceae) in a subtropical urban lake (30º03'05"S; 51º10'34"W) within the Botanical Garden, in the city of Porto Alegre, located in the state of Rio Grande do Sul, Brazil, in order to contribute to the floristic knowledge of Euglenophyta in artificial urban lakes. From July 2007 to June 2008, we collected samples monthly from two sampling stations, using a 25-µm mesh plankton net. The samples were preserved in 4% formaldehyde. We evaluated the following environmental variables related to the water in the lake: ammonia content, silica content, organic matter content, dissolved oxygen concentration, temperature, pH, depth, transparency, electrical conductivity and rainfall. To study the species composition in relation to environmental factors, we used cluster analysis, principal components analysis, canonical correspondence analysis and indicator species analysis. At the specific and infraspecific level, 22 taxa were identified, Trachelomonas elliptica (Playf.) Defl. and T. gracillima Bal. & Dast. representing new records for the state of Rio Grande do Sul. The cluster analysis indicated seasonal variation, species richness being highest in the spring of 2007. Seven indicator species were characterized as acid-tolerant.

O objetivo foi realizar um estudo taxonômico do gênero Strombomonas Deflandre em três trechos do arroio Bom Jardim, Município de Triunfo, RS, ampliando o conhecimento da sua riqueza e distribuição geográfica. As amostras foram coletadas mensalmente (2002-2006), com rede de plâncton e conservadas com formaldeído. Simultaneamente foram realizadas coletas d'água para medição de variáveis físico-químicas. Foram identificadas 26 espécies de Strombomonas, sendo que oito táxons apresentam distribuição cosmopolita e os demais estão restritos no máximo a três continentes. O agrupamento indicou que a maior similaridade ocorreu entre os trechos T2 e T3, igual a 82%, diferentemente de T1 (nascente). Esta diferença explica-se considerando que em T1 houve a presença exclusiva das espécies S. brevicaudata,S. scabra var. labiata e S. rotunda. S. brevicaudata Conf. é citada pela primeira vez para o Estado. S. eurystoma (Stein) f. incurva (Buz.) Pop. e S. recurvata Conf. & Joo são novos registros para o Brasil.

A taxonomic study of the genus Strombomonas Defl. was carried out in three reaches of the stream Bom Jardim, Municipality of Triunfo, Rio Grande do Sul State, expanding the knowledge of its richness and geographical distribution. Samples were collected monthly (2002-2006), with plankton net and preserved with formaldehyde. Simultaneously, water samples for measurement of physicochemical variables were collected. Twenty-six species of Strombomonas were identified; eight taxa have cosmopolitan distribution and the remainder are restricted to a maximum of three continents. The cluster analysis indicated that the greatest similarity occurred between the stream sections T2 and T3, equal to 82%, differently from T1 (upper reaches). This difference can be explained considering that in T1 the exclusive presence of the species S. brevicaudata,S. scabra var. labiata, and S. rotunda was verified. Strombomonas brevicaudata Conf. is registered for the first time in the State. Strombomonas eurystoma (Stein) f. incurva (Buz.) Pop., and S. recurvata Conf. & Joo are new records for Brazil.