Botrychium lunaria is a deciduous, perennial and somewhat fleshy, fern, 2-12 cm tall, most commonly found in open soil or meadows on slopes and floodplains. It is one of the diploid moonwort species having once-pinnate trophophores (vegetative leaves). Compared to other species of moonwort it is relatively uniform in morphology. The trophophores (vegetative leaves) are green, oblong, with 4-9 pairs of pinnae. The pinnae are fan shaped, symmetrical, usually overlapping each other but not the rachis, with entire to undulate margins. The basal pinnae are broadly fan-shaped with a span of 120 to 180 degrees, sessile or nearly so. The spore producing leaves (sporophores) are up to 2 times the length of the trophophore when spores are released and are 1-2 pinnate. Common moonwort, appropriately, is probably the most common moonwort in both Denali and interior Alaska. It looks most like B. tunux and B. yaaxudakeit. B. tunux has asymmetrical pinnae with sporophores that are shorter or equal in length to the trophophore and B. yaaxudakeit has basal pinnae that span greater than 180 degrees with pinnae that overlap the rachis.

Botrychium lunaria is perennial yet ephemeral, usually appearing in the spring and withering soon after spore release.

Moonworts have two generations: an underground haploid lifestage (gametophyte) and an aboveground diploid phase (sporophyte). The underground stage is much longer-lived and is entirely dependent on mycorrhizae for its survival. The gametophyte typically self-fertilizes and the movement of sperm underground is highly limited. The fertilized plant produces diploid tissues, several years later this will produce an aboveground, diploid plant. The aboveground plant is a single frond, with a sterile, photosynthetic leaf and a fertile leaf, bearing spores. The single-celled spores produced are dispersed by wind, becoming buried underground and developing into new gametophytes. Common moonwort sometimes hybridizes with other moonworts.

Occurs in well drained to moist sites.