The taxonomy of the genus Zannichellia is complex, with one species recognised throughout much of the World but with many taxa recognised at or below species level in different regions. The distinguishing characters for some taxa appear to be useful, but others appear to have been described based on very few samples and relatively minor morphological differences. Most taxa described to-date are treated as Z. palustris by Kew (The Board of Trustees of the Royal Botanic Gardens, Kew 2010). Multivariate analysis of morphometric data based on the Czech material did not support existence of any morphologically distinguishable taxa (Kaplan 2010).