Leaves and stems:

Leaves are evergreen, whorled or nearly so but spirally arranged with 8 to 10 leaves in a cycle, appearing as 8 to 10 columns when viewed from the side of the stem (8 to 10-ranked), and round in cross-section (like a bottle brush). Leaves are mostly spreading to ascending, up to ¼ inch (4 to 6 mm) long, to .9 mm wide, lance-linear, broadest near the base, dark green, toothless, and usually have a pale, sharp, spine-like tip. Stomata (pores) are usually moderately abundant on the upper surface.

Stems are horizontal, running above ground or buried just below the surface of the mossy floor, but not underground. At fairly regular intervals, erect shoots emerge that have up to 10 branches, most of which originate near the base of the shoot. Each year's new growth is marked by a distinct constriction where the annual bud grew, typically with a whorl of smaller leaves at that point. Horizontal stems are up to 6 feet long and the erect shoots up to 14 inches tall.

Spores:

Spores develop in spike-like or cone-like structures called strobili. Strobili are single at branch tips, ½ to 1 inch (1.5 to 2.5 cm) long, and stalkless. Each tiny spore sac is attached to a scale (sporophyll) that is about 1/8 inch (3mm) long, generally triangular and tapering to a slender, sharply pointed tip but lacks any hair-like extension. Scales are initially light green and tightly appressed, turning yellowish as they mature and light brown when dry, then become more spreading to release the spores in late summer into fall. The strobili persist through winter.

Notes:

Northern Clubmoss is a species of cool, shady conifer swamps and bogs, usually growing in a thick carpet of sphagnum moss, and reaches the southern edge of its range in Minnesota's northeastern counties. It is among the species formerly all lumped into Lycopodium, which have now been split into several genera. Distinguishing characteristics of these new genera are: whether spores develop in cone-like strobili or in leaf (or leaf-like) axils, whether strobili are stalked or stalkless, whether horizontal stems are above or below ground, whether branching on erect shoots is tree-like or not, the number of leaves in a spiral cycle, whether leaves are scale-like or not and whether they have a hair-like tip.

Northern Clubmoss is one of two Spinulum species known to be in Minnesota. It is distinguished by stalkless strobili that are single at branch tips, erect shoots have up to 10 branches, horizontal stems are above ground (or running through living moss), leaves are 4 to 6 mm long, not scale-like, broadest towards the base, have a minute spine-like tip, scattered stomata on the upper surface, and number 8 to 10 in a spiral cycle. The above ground stems, branching, and toothless leaves that lack a hair-like tip can help identify it even when strobili are not present.

The only other Spinulum species currently known to be in Minnesota is Stiff Clubmoss (S. annotinum), which is similar in all respects but is a more stout plant, leaves are larger, mostly more than 6 mm long, broadest above the middle, usually minutely toothed on the tip half, and lack stomata on the upper surface. The two were previously treated as vars of the same species, with S. canadense known as Lycopodium annotinum var. pungens or subsp. alpestre. Some references still lump them both under S. annotinum.

Compare with other clubmosses with cone-like strobili: Lycopodium species have long-stalked strobili and hair-like extensions on leaf tips, Dendrolycopodium have stalkless strobili but tree-like branching, and Diphasiastrum have stalked strobili and scale-like leaves. While several different clubmoss species may grow side by side, hybridization is not common.