3. Lycopodium tristachyum Pursh (blue ground-cedar)
Pl. 19i,j; Map 41
Diphasiastrum tristachyum (Pursh) Holub
Rhizomes 5–15 cm below the surface of the soil. Aerial stems erect, with
spreading to recurved branches. Ultimate branches flattened in cross-section.
Leaves of the ultimate branches 4-ranked, scalelike, those of the upper surface
1–2 mm long, appressed, those of the sides 3.5–5.5 mm long, spreading, those of
the lower surface 1–2 mm long, lanceolate, not overlapping. Strobili 3–4 at the
tips of the main aerial stems, 1–3 cm long, the tips obtuse to acute but not
attenuate with sterile portions, the leaves bearing the sporangia, 2.0–3.5 mm
long, dense, triangular. July–September.
Uncommon in Ste. Genevieve County (northeastern U.S.
and Canada south to Georgia and Alabama;
Asia). Moist ledges of shaded sandstone
bluffs.
As with L. dendroideum, the populations of L. tristachyum are
about 500 km disjunct from the nearest localities in Indiana
and Tennessee.
This species also has been interpreted as a relict from Pleistocene times.