The species concept in desmids: the problem of variability, infraspecific taxa and the monothetic species definition

Desmid systematics are much confused due to the existence of a very large number of infraspecific taxa, obscuring a clear species concept. The basis of this confusion is the huge morphological variability of desmid cells. Moreover, these ill-defined forms are frequently recombined back and forth with superficially related species, hence constantly changing species characterizations. In the present contribution the author will argue in favour of the utmost reserve with respect to the description of infraspecific taxa in desmids, the strict use of a monothetic species definition and a clear species concept.