1. Sporangia borne in the axils of regular leaves, not in strobili; stems bearing flattened, two-lobed gemmae that fall off and serve in vegetative reproduction.
1. Sporangia always born in terminal, differentiated strobili; gemmae absent.
2. Sporophylls (bracts subtending sporangia) green, leaf-like; erect branches with soft, herbaceous leaves, deciduous, unbranched (rarely forked) and always bearing terminal strobili; horizontal stems leafy, attached to substrate surface and rooting at frequent intervals.
2. Sporophylls yellowish, scale-like; sterile erect or ascending branches often present, these sometimes branched, all branches with evergreen, leathery leaves; horizontal stems either deeply buried or ± on the surface and rooting at irregular intervals.
3. Strobili sessile.
4. Leaves of sterile branches opposite and in ranks of 4, the branches ±square in cross-section.
4. Leaves of sterile branches in 5 or more ranks, the branches plus leaves flattened to rounded in cross-section.
5. Aerial stems simple or occasionally forked once with ascending branching; horizontal stems at the ground surface; strobilus one per upright shoot.
5. Aerial stems much branched and “tree-like,” with the branches often spreading; strobili usually several per upright shoot.
3. Strobili elevated on distinct peduncles.
6. Leaves spreading, lanceolate, acuminate and ending in a whitish, hair-like bristle.
6. Leaves appressed, partially fused with the stem, ± scale-like, in opposite pairs, the tips acute to acuminate, but lacking a whitish bristle.
Diphasiastrum (in part)