Arnica lessingii is a member of the aster family (Asteraceae) with solitary nodding yellow flowering heads and black anthers. This perennial herb grows up to 30 cm tall from a rhizome, found in cool, moist sites in alpine areas in meadows on tundra and most often in mossy ericaceous dwarf shrub tundra. The leaves are mainly basal, simple, lanceolate or elliptic, entire or toothed, pubescent above. The stem leaves are oppositely arranged close to the base of the stem and up to 14 cm long and 2.5 cm wide. Stems are also densely pubescent. The flowering heads are solitary, and usually nodding. The ray and tube flowers are yellow; the rays (petals) are oblong and toothed at the apex. The involucralbracts are moderately long-hairy with brown hairs and up to 17 mm tall. In fruit, the flowering head matures into many narrow achenes, each topped with a tuft of brown or tawny hairs, the pappus. Black anthers and a brown pappus distinguish this Arnica species from others that occur in the park.
Nodding arnica flowers from June through August.
The showy yellow flowers of this species are likely insect pollinated, but its reproductive biology has not been studied. Plants are monoecious. The seeds have a tuft of hairs to aid in wind dispersal. Plants may also reproduce vegetatively.
Nodding arnica is an amphi-Beringian endemic species occurring in Alaska, northern British Columbia, Yukon Territory, Northwest Territories and eastern Asia. This species occurs occasionally in arctic-alpine regions of Alaska and on both sides of the Alaska Range and foothill ranges in Denali.
Nodding arnica is a primarily alpine plant in Denali with a preference for moderate slopes. It occurs almost as frequently on north-facing slopes as it does on south-facing slopes at a wide range of elevations (500 - 1500 m) and on a wide range of inclines in both slope classes (1 - 41 degrees). The average elevations and inclines are similar for both aspect classes (approximately 1100 m elevation and a 16 degree incline).