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).

Throughout most of its range, there are no significant taxonomic issues associated with this name. However on the southern border of its distribution its taxonomy is less clear (Wiegleb and Kaplan 1998). The ecotype with oblong-lanceolate, 30-40 cm long leaves growing in some rivers in the European part of Russia and Russian Central Asia has been treated as an independent species; Potamogeton longifolius J. Gay. In the southern regions of European Russia smaller forms of P. lucens are found which resemble P. sarmaticus (Tzvelev 2001). Potamogeton lucens has been shown to hybridise with P. alpinus (P. xnerviger Wolfg. in Schult. et Schult.), P. crispus (P. xcadburyae Dandy et G. Taylor), P. gramineus (P. xangustifolius J. Presl in Bercht. et J. Presl), P. natans (P. xfluitans Roth) and P. perfoliatus (P. xsalicifolius Wolfg. in Schult. et Schult.). Of these, P. xsalicifolius is relatively widespread but usually occurs with one or both parents whereas P. xangustifolius is also widespread but is one of the few Potamogeton hybrids which often produces fertile seed and frequently occurs in the absence of both parents. It is possible that these hybrids could obscure the true distribution of P. lucens, but unlikely that they represent a threat to its survival.

Linaria hellenica Turrill is often treated under the synonym Linaria tenuis (Viv.) Sprengel (Commission of the European Communities 2009). Euro+Med Plantbase accepts Linaria hellenica as a valid name.

The genus Scoliodon, represented by S. laticaudus, was previously considered monotypic but now consists of three species with S. macrorhynchus resurrected from the junior synonym of S. laticaudus (White et al. 2010).