Alexandrium is a genus of dinoflagellates, with many species related to toxin production leading to paralytic shellfish poisoning. The dinoflagellate cysts produced by this species are considered much more toxic than swimming cells. Enzyme electrophoretic data and RNA genetic analysis show two of the species, Alexandrium fundyense and A. tamarense to be closely related, while mating compatibilities even suggest them to be varieties of a single heterothallic species.