The morphology of 61 planktonic populations of the genus Anabaena with coiled trichomes was studied under natural conditions. Samples were collected from Czech water bodies and represent all morphospecies of coiled Anabaena that have previously been reported from the Czech Republic. Using the Principal Component Analysis (PCA) and paired t-tests, the existence of clear morphological boundaries of these morphospecies was tested. The only clearly delimited morphospecies found was A. compacta, which is defined by the width of vegetative cells, the shape of akinetes and the regularity of coiling. The other morphospecies formed a morphological continuum and no clear-cut boundaries could be observed. Defined groups of morphotypes were thus proposed for practical usage, specifying also the morphological criteria (A. mendotae & A. sigmoidea, A. flos-aquae & A. spiroides, and A. circinalis & A. crassa). Identification of the studied Anabaena morphotypes at a lower taxonomic level is not feasible based only on morphology. Moreover, A.lemmermannii taxon appears to be morphologically heterogeneous and requires a thorough taxonomic revision.