Leaves and stems:

Leaves are of two types: fertile (sporophylls) bearing spore sacs, and sterile (trophophylls) lacking spores. Both are evergreen, similar in shape, narrowly triangular, broadest at the base, pointed at the tip, toothless, with stomates (pores) on both the upper and lower surface, the larger leaves with 35 to 60 per half leaf on the upper surface. Leaves on the lower stem (juvenile portion) are longest, 4 to 6 mm (to ¼ inch) long and spreading to ascending; leaves on the upper stem (mature portion) are shorter, about half the size of the longest leaves, and ascending to appressed. In shady habitats, leaves tend to be longer and more spreading than in sunnier habitats.

Leaves may appear whorled or nearly so but are spirally arranged with about 8 leaves in a cycle, more or less evenly spaced and may appear as columns when viewed from the side of the stem (8-ranked). Stems are erect, single or multiple from the base, unbranched or with forked branches, the branches mostly erect. Each year's new growth is not marked by any conspicuous constriction where the annual bud grew.

Spores:

Spore sacs (sporangia) develop on most of the current year's growth, one sac attached to the base of each sporophyll on the upper stem and branches, turning yellow as they mature and light brown when dry, splitting open to release the spores in late summer into fall. Old, dried sporangia from previous years persist on the stem.

Leaf-like propagules (gemmae) are also produced on claw-shaped branchlets distributed throughout the stem. Gemmae are flattened fan-shaped, 3 to 4 mm long with 3 main leaves, the central leaf oblong and the 2 lateral leaves more elliptic, .5 to 1 mm wide, and all 3 pointed at the tip.

Notes:

Appalachian Firmoss, formerly known as Huperzia appalachiana, or included with Lycopodium selago in older references, is one of 4 Huperzia species known to be in Minnesota and one of the rarest. According to the DNR, only about 20 small populations are known, mostly concentrated in Lake County near the shore of Lake Superior. The cliff and talus microhabitats required by this species are vulnerable to human activities from rock climbing to logging. It was listed as a Special Concern species in 2013 and is currently also Special Concern in Wisconsin.

Appalachian Firmoss has the smallest leaves and gemmae of the Minnesota Huperzia species, but it is most easily recognized by the distribution of the gemmae all along the stem, where the other species have gemmae only whorled around the annual bud. The claw-shaped branchlets persist long after the gemmae have dropped off so it can be identified any time of year. It hybridizes with both Northern Firmoss (Huperzia selago) and Shining Firmoss (Huperzia lucidula). Hybrids may have intermediate characteristics but have aborted spores.