Leaves and stems:

Leaves are of two types: fertile (sporophylls) bearing spore sacs, and sterile (trophophylls) lacking spores. Both are evergreen, dark green, mostly spreading to reflexed, somewhat shiny, pointed at the tip, and with stomates (pores) only on the lower surface. The largest leaves are 7 to 11 mm (to nearly ½ inch) long, broadest at or above the middle, minutely and irregularly toothed on the tip half with 1 to 8 teeth per side. The shortest leaves are around the annual bud, about half the size of the largest leaves and broadest at or below the middle.

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), though not always strongly so. Leaves form a wavy outline of long and short leaves along the stem, the short leaves marking the annual constriction. Stems are single or multiple from the base, unbranched or with forked branches, the branches mostly erect, the lower stem initially erect but may become prostrate with age then rise at the tip (decumbent). Plants may form colonies.

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 late in the season on claw-shaped branchlets in a single whorl around the tip of the current year's growth. Gemmae are flattened fan-shaped, 4 to 6 mm long with 3 main leaves, the central leaf oblong and the 2 lateral leaves broader and somewhat angular, broadest near the tip, 1.5 to 2.5 mm wide, and all 3 with a minute point at the tip (mucronate).

Notes:

Shining Firmoss, known as Lycopodium lucidulum in older references, is the most common of the 4 Huperzia species known to be in Minnesota. It has the largest leaves and gemmae of the Minnesota Huperzia species, but it is most easily recognized by the toothed leaves broadest above the middle with stomates only on the underside (magnification required to see), and the single whorl of gemmae branchlets around the annual bud. The claw-shaped branchlets persist long after the gemmae have dropped off so that can be seen any time of year. This species can form sizable colonies, unlike the others.

Shining Firmoss is also almost always found in soil, in moist to wet woods and rarely on rocks, which distinguishes it from both Rock Firmoss (Huperzia porophila) and Appalachian Firmoss (Huperzia appressa, a.k.a. H. appalachiana), which are always found on rock, usually cliff ledges and crevices or talus slopes. The wavy outline of alternating long and short leaves along the stem is a trait shared with H. porophila, but leaf size, shape and habitat distinguishes these two, and also contrasts with Northern Firmoss (Huperzia selago), which has leaves mostly all of similar size that are narrowly triangular in shape, not toothed, and more often ascending to appressed rather than spreading or reflexed. H. lucidula hybridizes with both H. selago and H. porophila; hybrids may have intermediate characteristics and scattered stomates on the upper leaf surface, but have aborted spores.