Nodularia Mertens ex Bornet & Flahault originally established in 1822, has had a total of 28 taxa described. It is restricted in distribution primarily to brackish coastal waters and inland lakes and ponds. In British Columbia (Canada) these lakes and ponds have extreme ranges of salinity (4–400‰) and temperature (0–35 °C). Laboratory studies of 16 isolates indicated maximum growth at 5–10‰, salinity (range 1–60‰), 25–30 °C, pH 10.0–10.5 (range 7.0–10.5) at light intensity of 6000 lx. No preference was shown for dominant anions (Na+, Mg2+) or cations (Cl−, CO32−, S42−). Sheath and akinete characteristics were variable, whereas vegetative cell shape, heterocyst location, and akinete formation were more stable. Investigation of field-collected material, laboratory-grown cultures, and study of herbarium specimens indicate that all the described taxa belong to either N. harveyana [Thwaites] Thuret ex Bornet & Flahault 1886 or N. spumigena Mertens ex Bornet & Flahault 1886. The latter is named the syntype and lectotype material is designated.