The spores of Lycopodium deuterodensum germinate after 3 weeks in the dark on a nutrient medium containing inorganic nutrients and glucose. The dark grown prothalli have the characteristics associated with Type I and II gametophytes – a ring meristem, radial symmetry, and lack paraphyses and photosynthetic lobes. The younger gametophytes have the carrot shape of a Type II gametophyte with a tapering base, a constricted neck, and a gametangial cap with antheridia. With additional growth, the gametophytes become as wide as long and finally wider than long. The wider than long gametophytes are the first to have both antheridia and archegonia on their gametangial caps. The largest gametophytes grown in culture are Type I with irregular disk shapes. The antheridia on all gametophytes are sunken and, for the Lycopodiaceae, the archegonia have medium sized necks with only 3–4 neck canal cells. Although the specific type of gametophyte has not been determined for this species, those grown in culture have the characteristics recognized for subterranean, nonphotosynthetic, mycorrhizal gametophytes of the Lycopodiaceae.