C. cordata is what's known as a "superspecies" or "species complex" that is, it is not a single plant but extremely polymorphic, possibly more so than other Cryptocoryne species.
These are some of the species, all uniquely identifiable plants, that we now know are just cordata.
Most of these were described by Rataj, and while it may be true to say if he'd looked at the karyotype might have noticed they were all the same or very similar hinting at a single spcies, it's also true that even if they aren't all still species this information is useful to demonstrate some of the types of COR and SIA that exist and the range and limits of polymorphism that occurs with very plastic species.
