Plants mainly trailing on ground. Roots emerging from point of origin on underside of main stems. Horizontal stems on substrate surface or subterranean, long-creeping. Upright shoots scattered along horizontal stem, 5–16 mm diam., round or flat in cross section, unbranched or with 1–4 lateral branchlets. Leaves not imbricate, linear to linear-lanceolate; leaves on horizontal stems scattered, appressed, membranous; leaves on lateral branchlets mostly 6-ranked or more, monomorphic with few exceptions, appressed, ascending to spreading, margins entire to dentate. Gemmiferous branchlets and gemmae absent. Strobili single and sessile or multiple and pedunculate, apex blunt to acute; peduncle, when present, conspicuously leafy; sporophylls extremely reduced, much shorter than peduncle or stem leaves. Sporangia reniform. Spores reticulate, sides at equator convex, angles acute. Gametophytes nonphotosynthetic, mycorrhizal, subterranean, flat and irregularly button-shaped, with ring meristem around circumference. x = 34.

Distribution

Mainly temperate and subarctic.

Discussion

In striking contrast to Diphasiastrum, Huperzia, and Lycopodiella, interspecific hybridization is practically unknown in Lycopodium. Many of the species now recognized in Lycopodium have been segregated from Lycopodium clavatum, L. annotinum, and L. jussiaei Desvaux ex Poiret. The three groups given in the key below should probably be treated as subgenera.

Species 15–25 (6 in the flora).

Selected References

Hickey, R. J. 1977. The Lycopodium obscurum complex in North America. Amer. Fern J. 67: 45--49.

Wagner, W. H. Jr., J. M. Beitel, and R. C. Moran. 1989. Lycopodium hickeyi: A new species of North American clubmoss. Amer. Fern J. 79: 119--121.

Lower Taxa

Lycopodium annotinum, Lycopodium clavatum, Lycopodium dendroideum, Lycopodium hickeyi, Lycopodium lagopus, Lycopodium obscurum

Key

1	Strobili pedunculate; upright shoots with 2–5 branches, not treelike; leaves with hair tips 1–4 mm (these may fall off early, but remain at shoot apices) (L. clavatum group).	> 2
1	Strobili sessile; upright shoots either unbranched or much branched to produce treelike habit; leaves lacking hair tips.	> 3
2	Strobili mostly solitary on peduncle, if paired then nearly lacking pedicels; leaves 3–5 mm, ascending to appressed; branches 2–3(–4), mostly upright.	Lycopodium lagopus
2	Strobili 2–5, borne on loosely alternate pedicels, 0.5–0.8 cm; leaves 4–6 mm, spreading to somewhat ascending; branches 3–6, mostly oblique or spreading.	Lycopodium clavatum
3	Strobili single at top of upright shoot; shoot unbranched or branched 1–2 times; horizontal stems on substrate surface (L. annotinum group).	Lycopodium annotinum
3	Strobili 1–7 at top of many-branched, upright, treelike shoot; horizontal stems subterranean (L. dendroideum group).	> 4
4	Lateral shoots flat in cross section, leaves unequal in size, lateral leaves spreading and twisted, adaxial surfaces facing upward, proximal leaves much reduced; leaves on main axis dark green, tightly appressed.	Lycopodium obscurum
4	Lateral shoots round in cross section, leaves equal in size, none twisted, adaxial leaf surfaces all facing stem, proximal leaves not reduced; leaves on main axis light or dark green, spreading or appressed.	> 5
5	Leaf ranks 1 on upperside of lateral branch, 2 on each side, and 1 on underside; leaves of main axis below branches dark green, tightly appressed, soft to touch.	Lycopodium hickeyi
5	Leaf ranks 2 on top of lateral branch, 1 on each side, and 2 on underside; leaves of main axis below branches pale green, spreading, prickly to touch.	Lycopodium dendroideum