The genus is generally divided into two groups: broad-leaved and linear-leaved. The broad-leaved group includes such species as "P. natans", "P. perfoliatus" and "P. alpinus". The linear-leaved group includes such species as "P. rutilus", "P. compressus" and "P. berchtoldii". Series "Batrachoseris" historically contained only one species, "Potamogeton crispus," however more recent research has also added "P. maackianus" and "P. robbinsii" into this grouping. These general divisions have been supported by molecular analysis, except that "P. crispus" clusters with broad-leaved species in section "Potamogeton".