This is a widespread eastern species, but generally absent on base-rich soils. Some colls. may need rechecking for tristachyum (Cranfill 1980), and rare hybrids with tristachyum (L. X habereri House) may be expected (FNA 2). The genus Diphasiatrum differs from other Lycopodioideae (Lycopodium, Dendrolycopodium, Spinulum) as folllows (FNA 2, W): branches 1-6 mm wide including the leaves (versus 4-12 mm), generally compressed to quadrangular (versus terete to somewhat compressed), with 4-5 ranks of leaves (versus 6 or more), mostly imbricate (versus not so); branching of strobilus stalks, if present, dichotomous (versus pseudomonopodial, falsely appearing to have a main axis from which branches alterantely arise); gametophytes carrot-shaped (versus disc-shaped).