Diphasiastrum alpinum is a creeping clubmoss (Lycopodiaceae) with unstalked strobili, and branched erect stems which are square in cross section. Diphasiastrum alpinum is typically found in alpine heaths and meadows in snowbed areas. Horizontal stems are up to 50 cm long, erect stems reach up to 10 cm high. It has a bluish-green appearance, and strongly overlapping, four-ranked leaves in two shapes: lanceolate and appressed on the dorsal side, and deltoid-ovate laterally. The 'strobili' are not stalked and are solitary at the branch tips, which (along with habitat differences) distinguishes it from the other common clubmoss of this genus found in the park, Diphasiastrum complanatum. It could also be confused with the rare Diphasiastrum sitchensis that occurs only on the south side of the Alaska Range in Denali, which has five-ranked leaves all the same shape and a stem round in cross section.
Diphasiastrum alpinum is an evergreen perennial. Spores are produced in mid-summer.
The visible portion of Diphasiastrum alpinum is a diploid sporophyte. These plants are produced from a haploid lifecycle, which lives underground and is entirely dependent on mycorrhizae for its survival. The haploid gametophyte self-fertilizes (rarely out-crossing) and produces an independent, photosynthetic sporophyte (the plant described and pictured). sporophytes produce single-celled spores, which are wind-dispersed and develop into new underground gametophytes.
The fungus Leptoshpaeria lycopodina has been documented infecting the leaves and bracts of Diphasiastrum alpinum (Ellis and Ellis 1997 In Peat et al. 2015). The larvae of a micro-moth, Catoptria furcatellus, feed on the leaves of species in the family Lycopodiaceae (Emmet 1991 In Biological Records Centre 2008).
The clubmosses (Diphasiastrum and Lycopodium are used by the Dena'ina to make an eye wash (Kari 1995). Other species in these genera which occur primarily in forested areas were used medicinally by indigenous people throughout North America and Europe (Moerman 1998, Schofield 1989).
Alpine clubmoss is an incompletely circumpolar species with a boreal-montane distribution. Diphasiastrum alpinum occurs in Iceland, Norway, Russia, Siberia, the Russian Far East, and in North America from Greenland to Alaska, and south to British Columbia, Michigan, Washington and Montana. This species is common in sub-alpine and alpine plant communities throughout Alaska except for north of the Brooks Range. It occurs in scattered sites on both side of the Alaska Range in Denali (although it is most common on the south side).
Alpine clubmoss occurs at 338 -1352 m elevation in Denali, however most of the occurrences are above 900 m. Of the seven other clubmosses occurring in the park, it is most similar in elevation to another clubmoss Huperzia selago. It occurs more frequently on south-facing slopes (50% of occurrences), then on north-facing slopes (36% of occurrences) but at similar altitudes. It occurs on slopes with inclines up to 45 degrees, but more frequently with mild to moderate inclines between 12 and 28 degrees.