NOTES: See the parent taxon for further description. The two varieties differ primarily in the size of the fruit, the Arizona specimens are of the common var. heterophylla with fruits 0.6-0.8 mm long, rather than in var. bolanderi (Hegelm.) Fassett with fruits 0.8-1.3 mm long. 2n = 20. Lakes, ponds and slow-moving streams: Apache, Cochise, Coconino, Gila, Graham, Pima, Pinal cos.; 900-2750 m (3000-9000 ft); Feb-Aug (fr. May-Oct); throughout N. Amer., scattered in W. Ind., C. Amer., S. Amer. and New Zealand. REFERENCES: Ricketson, Jon. 1995. Callitrichaceae. J. Ariz. – Nev. Acad. Sci. 29(l): 15.