From Flora of the Indiana Dunes (1930) - Donald C. Peattie
L. obseurum L. var. dendroideum (Michx.) D. C. Eaton. Rootstock rope-like, subterranean, the upright stems like little trees, dichotomously forking; leaves very narrow, 6-ranked, incurved or erect; spikes 1-15.—In rich cool woods, Pine and Miller.
Horizontal stems subterranean. Upright shoots treelike, many branched, branchlets numerous and strongly differentiated; annual bud constrictions absent; leaves spreading, pale green below lateral branchlets, prickly needlelike, 3.5--4 X 0.9--1 mm. Lateral branchlets round in cross section, 5--8 mm diam.; annual bud constrictions inconspicuous; leaves spreading to ascending, pale green, in 6 ranks, 2 upperside, 2 lateral, and 2 underside, equal in size, linear, 2.4--5.5 X 0.5--1.2 mm; margins entire; apex acuminate, lacking hair tip. Strobili sessile, 1--7 on tip of upright shoot, 12--55 mm. Sporophylls 3.5 X 3.5 mm, apex short, acute, abruptly narrowing. 2 n = 68. Dry woodlands and second-growth shrubby areas; 50--1800 m; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska, Conn., Idaho, Iowa, Maine, Mass., Mich., Minn., Mo., Mont., N.H., N.Y., Pa., S.Dak., Vt., Va., Wash., W.Va., Wis., Wyo.; Asia.
Perennial fern ally 9 - 30 cm tall Leaves: of lateral branches in six ranks (two ranks each on upper and lower sides, one rank on each lateral side, but all of same size), stalkless, spreading to ascending, non-toothed, pale green, 2.4 - 5.5 mm long, 0.5 - 1.2 mm wide, linear with a long, tapering, narrow, pointed tip (but no hair at very tip). Rhizomes: buried under soil surface. Spores: hundreds per sac, all of one kind, 20 - 40 microns in diameter, thick-walled, veiny, three-sectioned (trilete) with pointed angles. The spores give rise to the gametophyte (the sexual phase of the plant), which is small, flat, disc- or button-shaped, underground, not green, but saprophytic, and inhabited by symbiotic fungi (mycorrhizae). Stems: upright, green, tree-like with many branches and numerous, differentiated, ascending, 5 - 8 mm diameter, lateral branchlets, which are round in cross-section. Below the branches, the main stems are covered with pale green, spreading, prickly, 3.5 - 4 mm long, 0.9 - 1 mm wide, needle-like leaves.
Similar species: Lycopodium dendroideum is incredibly similar to L. hickeyi, but that species has only one rank of leaves on the upper side and underside of the lateral branchlets but two ranks of leaves on each lateral side of the branchlets, and the leaves on the main stem below the branches are dark green, tightly appressed, and soft to the touch. Also very similar is the more northeastern species L. obscurum, but the lateral shoots of that species are flattened in cross-section, the leaves are of unequal sizes, the lateral leaves spread and twist such that the underside of the leaf faces up, and the leaves on the main stem are dark green and tightly appressed.
Habitat and ecology: Rare, in beech-maple woods, and also in wet-mesic swamps behind dunes.
Occurence in the Chicago region: native
Notes: Many floras still refer to this species as Lycopodium obscurum, though that name should only be applied to plants more northeast of the Chicago Region. Lycopdoium dendroideum has the most expansive range of the three species in the L. dendroideum group (this species, L. hickeyi, and L. obscurum).
Author: The Field Museum
Citation: The vPlants Project. vPlants: A Virtual Herbarium of the Chicago Region. http://www.vplants.org
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