Leaves and stems:

Leaves are of two types: fertile (sporophylls) bearing spore sacs, and sterile (trophophylls) lacking spores. Both are evergreen, pointed at the tip, narrowly triangular, broadest at or near the base, with stomates (pores) on both the upper and lower surface, the larger leaves with 30 to 90 per half leaf on the upper surface. Leaves are hollow at least at the base, giving them a thickened look. The largest leaves are 4 to 7.5 mm (to ~1/3 inch) long, the shortest leaves are around the annual bud, only slightly smaller than the largest leaves. In sunny habitats, leaves are mostly ascending to appressed and often turn yellow; in shadier habitats, leaves tend to be more ascending to spreading and green.

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 are more or less the same length all along the stem, the shorter leaves not usually marking the annual constriction very conspicuously. 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).

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 in a single whorl around the tip of the current year's growth. Gemmae are flattened fan-shaped, 4 to 5 mm long with 3 main leaves, the central leaf oblong and the 2 lateral leaves slightly broader and rounded to somewhat angular, broadest near the tip, 1.5 to 2 mm wide, and all 3 with a minute point at the tip (mucronate).

Notes:

Northern Firmoss, known as Lycopodium selago in older references, is a circumboreal species present in northern Europe and Asia, most of Canada and just creeping into the US in New England and around the Great Lakes. It has the most varied habitat of the 4 Huperzia species known to be in Minnesota, found in conifer swamps, bogs, forests, mossy banks, peaty shores, cliffs, talus slopes, tailings basins and borrow pits, in sun or shade, soil or rocks, usually moist to wet conditions, sometimes dry.

It is also the most variable Huperzia, depending on environmental conditions: in sunny spots it may have nearly appressed leaves that are all about the same size along most of the stem, can be distinctly yellow with a moderate number of stomates on the upper surface, whereas in shadier places shorter leaves indicate a more conspicuous annual constriction, leaves are more spreading, green, and have abundant stomates on the upper surface. The longest leaves are up to 7.5 mm long, toothless and generally triangular in outline, widest at or near the base, but also has another characteristic that makes it unique: leaves with a hollow core. We learned about this trait on the DNR's Huperzia porophila rare species page and were surprised to discover it is true: the leaves of the other Huperzia species are decidedly flat where H. selago look more inflated (especially towards the base) due to the hollow core, though we have not investigated any differences in sunny vs. shady habitats. Yet.

Of the other Huperzia species in Minnesota, Rock Firmoss (Huperzia porophila) and Appalachian Firmoss (Huperzia appressa, a.k.a H. appalachiana) are always found on rock, usually shady cliff ledges and crevices or talus slopes. H. porophila leaves are mostly linear-oblong, the sides parallel for most of their length before tapering to a pointed tip. H. appressa has smaller leaves (2 to 3.5 mm on the upper stem) and those on the lower stem are usually longest. Shining Firmoss (Huperzia lucidula) is usually found in soil, rarely on rocks, and has the largest leaves (8 to 12 mm) that are broadest above the middle and irregularly toothed. H. selago hybridizes with both H. lucidula and H. appressa; hybrids may have intermediate characteristics and scattered stomates on the upper leaf surface, but have aborted spores.