Hooded ladies tresses is a wetland orchid with a spiraling spike of delicate white flowers. This species grows in wet meadows in the boreal zone in Denali on both sides of the Alaska Range. Plants grow 10-30 cm tall, with a few linear basal leaves. The roots are fleshy and tuberous. Stem leaves are sheathing and alternate. The upper leaves are highly reduced bracts. The inflorescence is a dense cylindrical spike, with flowers arranged in spirals of four. Flowers are bilaterally symmetric and have specialized morphology typical to orchids. Flowers are white at the tips, becoming greenish at the base. The upper petal and the two sepals are fused to form a curved hood, the lower lip curves back towards to stem. Fruits are cylindric capsules containing many tiny seeds. Spiranthes romanzoffiana could potentially be confused with Platanthera dilatata, another orchid with a spike of spiraling white flowers, if one hadn't seen both species. In that species, the flowers have elongate, wing-like petals. Spiranthes romanzoffiana has a much thicker, tightly spiraled inflorescence, and the flowers are more tubular.
Hooded ladies tresses is perennial. The flowers appear in mid-summer and are protandrous-the stamens developing before the stigmas.
Like all orchids, each flower contains a set of pollinia. These packages of pollen attach to bees, which in turn pollinate other flowers. Hooded ladies tresses is an outcrossing species (Catling 1982). The capsules release hundreds of minute, dust-like seeds, which are wind-dispersed. Like all orchids, the species is dependent on its mycorrhizae for its establishment and nutrition.
Spiranthes romanzoffiana occurs broadly in North America and is endangered in the British Isles (Ireland & western Scotland). In North America, the species occurs throughout Canada, except for the high arctic, to the Great Lakes and New England in the East, and in most of the Western states, with an interrupted distribution in the Southwest. In Alaska, Hooded lady's-tresses is known from the southern edge of the Brooks Range, to Unimak Island in the eastern Aleutians, through the mainland of Alaska and southeastern panhandle. In Denali, this species occurs in boreal lowlands of the Park, both north and south of the Alaska Range.
Hooded lady's tresses grows from low elevations to the subalpine, average site at 370 m. This species is almost always on flat areas, the few plants found above five degrees incline in Denali were on low south-facing slopes.