Isolates of the genera Monoraphidium Kom.‐Legn., Ankistrodesmus Corda and Raphidocelis Hindák emend. Marvan et al. were cultured from two areas in Minnesota and North Dakota, USA. These isolates were identified to species level (when possible), using light microscopy and standard monographs and then characterized by 18S rDNA sequence analysis. Phylogenetic analyses indicated that in some cases, 18S rDNA sequences from these isolates were very similar, but not identical to the sequences of other isolates of the same morphospecies from different parts of the world. However, some isolates that were identified as the same species actually belong to different lineages within the Selenastraceae, whereas other isolates with identical or nearly identical 18S rDNA sequences possessed rather different morphologies. Overall, our data suggest that the application of a broad morphospecies concept to the Selenastraceae has resulted in an underestimation of the species diversity of this family and probably erroneous conclusions about the distribution of species.

Through the use of molecular techniques, several different types of fusiform and twisted‐fusiform microchlorophyte algae (Monoraphidium, Ankistrodesmus, etc.) have been characterized from samples taken from lakes and ponds of Itasca State Park, MN. PCR–RFLP analysis of 18S ribosomal RNA genes was used to categorize 29 different isolates from the Itasca State Park lakes into nine different types. The 18S ribosomal DNA sequences were determined for one isolate from each type for phylogenetic analysis. Light microscopy was used so that morphological characteristics as well as molecular characteristics can be compared and contrasted. The morphological characteristics were consistent for each PCR–RFLP type. Further discussion will include comparisons of the distribution and diversity of these organisms from Itasca State Park to those from Arrowwood National Wildlife Refuge, ND.

Several types of fusiform microchlorophyte algae (Monoraphidium, Ankistrodesmus, and related genera) have been characterized from lakes and ponds of Itasca State Park, Minnesota, and Arrowwood National Wildlife Refuge, North Dakota. PCR‐RFLP analysis of 18s ribosomal RNA genes was used to categorize 29 different isolates from Itasca State Park into 9 different types, and 15 isolates from the Arrowwood National Wildlife Refuge samples into 8 different types. 18S ribosomal DNA sequences were determined for at least one isolate from each type for phylogenetic analysis. All of these sequences were different than any sequence published in GenBank. None of the types were found in both Itasca State Park and Arrowwood National Wildlife Refuge. These results suggest that fusiform green algae are highly diverse, with little species overlap in different habitats.