Lycopodium porophilum F. E. Lloyd & L. Underwood, Bull. Torrey Bot. Club 27(4): 150. 1900; L. lucidulum Michaux var. porophilum (F. E. Lloyd & L. Underwood) Clute; L. selago var. porophilum (F. E. Lloyd & L. Underwood) Clute; Urostachys lucidulus (Michaux) Nessel var. porophilus (F. Lloyd & L. Underwood) Nessel

Shoots erect, determinate, occasionally indeterminate, 12--15 cm, clustered to short-decumbent, leaves of mature portion slightly smaller than leaves of juvenile portion; annual constrictions distinct to indistinct; juvenile growth erect. Leaves reflexed at base, ascending at stem apex (forming cluster) and spreading for most of stem length, sparse, yellow-green (juvenile portion) to yellow-green to green (mature portion), lustrous; largest leaves lanceolate with roughly parallel sides, 5--8 mm; smallest leaves triangular, widest at base, 3--6 mm; margins almost entire with low papillae or a few large teeth; stomates on both surfaces, few (1--25 per 1/2 leaf) on adaxial surface. Gemmiferous branchlets produced in 1--3 pseudowhorls at end of annual growth; gemmae 4--5 X 3--4 mm; lateral leaves 1--1.5 mm wide, acute, widest above middle. Spores 29--38 µm.

On damp, shaded, acidic sandstone, rarely on shale or exposed sandstone; 50--1200 m; Ala., Ill., Ind., Iowa, Ky., Minn., Mo., Ohio, Pa., Tenn., Va., W.Va., Wis.

Huperzia porophila occurs in several disjunct populations, most notably in the Driftless Area of Iowa, Minnesota, and Wisconsin. A sterile hybrid between H . porophila and H . lucidula , H . × bartleyi , occurs throughout the range of H . porophila . It reproduces vegetatively by gemmae and is common in habitats intermediate between those of the two parents. In Ohio the hybrid may occupy sites to which H . porophila would otherwise be restricted, thus reducing the sites available for colonization by H . porophila (A. W. Cusick 1987).