Huperzia haleakalae is a common alpine clubmoss with strobili borne along the stem in the axils of its needle-like fertile leaves, not in terminal 'cones' as occurs in the genus Lycopodium. This species occurs primarily in alpine tundra and openings in shrub tundra areas, particularly in mossy places dominated by heath species and snowbed sites. As is true of all our clubmosses, its stems are covered in scale-like leaves with single, unbranched veins. Stems of one plant reach the same height, and can grow 8-12 cm tall. Leaves are triangular. Unlike other clubmosses, Huperzia haleakalae does not produce separate spore-producing structures (strobilii) above the vegetative stems. Instead, these structures occur in axils of fertile spore-producing leaves along the stem. These occur in distinct rows.
Huperzia haleakalae is perennial and evergreen. Each year, stems initially grow a set of photosynthetic leaves and then a row of fertile leaves. You can thus roughly determine a plant's age. Spores are produced in mid-summer.
The visible portion of Huperzia selago is a diploid sporophyte. These plants are produced from a haploid gametophyte, which lives underground and is entirely dependent on mycorrhizae for its survival. The haploid gametophyte self-fertilizes 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. Plants also produce vegetative propagules (gemmae). These are leaf-like, produced between leaves along the stem, they easily break off and spread the plant.
Huperzia haleakalae is an amphi-Beringian species occurring in mountainous areas. In North America, H. haleakalae ranges from the Manitoba in the east to Alaska, and south along the Rocky Mountains to Colorado (and also in Hawaii, as its name implies). Within Alaska, Huperzia haleakalae occurs across mountainous areas of the state, although it is not common north of the Brooks Range. It is widespread and reasonably common in Denali, occurring on both sides of the Alaska Range with some isolated occurrences in the northwestern lowlands.
Huperzia selago is an alpine species, most frequently found above 1100 meters. It has a marked preference for northern aspects, and plants found on those sites occur over a wider range of elevations and slopes. It occurs most commonly on steep slopes (20-28 degrees).