Castilleja caudata is a tufted perennial herb with narrow-lanceolate leaves and a spike of pale yellow flowers, typically found in open floodplains and open soil on well-drained slopes. Plants grow 20-40 cm tall from a branched taproot.
The leaves are alternately arranged and without petioles, with parallel, curving veins. Lower leaves are narrowly lanceolate, becoming broader and shorter further up the stems. The stems are purple reddish, unbranched. The lower half of the plant is hairless, becoming short-pubescent, and long white-haired in the inflorescence.
At the top of the stem, the plant produces a dense cluster of several yellow flowers. Flower buds are also sometimes produced in the upper axils. The bracts below the flowers are entire to deeply cleft into narrow segments, greenish or reddish in color. They subtend the four-lobed, yellow calyx, which is nearly as long as the petals. The petals are two-lipped, the upper lip more than 5 times as long as the lower lip. The species' fruit is a dry capsule, 9-10 mm long, which splits along one seam to release numerous seeds.
This is the only pale yellow-flowered paintbrush species in Denali, the other member of the genus is the usually magenta-flowered and appropriately named tundra species C. elegans. Species of the genus Castilleja are hemi-parasites: they produce their own sugars through photosynthesis, but also form connections to the roots of other plants to divert nutrients and water for their own use.
Castilleja caudata is a semi-parasitic perennial species, re-sprouting every year from its taproot. This species flowers in mid to late summer.
Castilleja caudata is monoecious with bisexual flowers. Pale-flowered Castilleja species tend to be either insect pollinated (by Bombus bees) or self-fertile (Duffield 1972). The reproductive biology of C. caudata has not been studied. The species' fruit is a dry capsule, which splits along one seam to release numerous seeds, dispersed by gravity and water. Species of the genus Castilleja are hemi-parasites: they produce their own sugars, but also form connections to the roots of other plants to steal nutrients and water.
Castilleja caudata is an amphi-Beringian endemic species. Castilleja caudata occurs from Chukotka across Alaska to western Northwest Territories. In Alaska, Castilleja caudata occurs from the Arctic slope to the mountain ranges in the southcentral region. In Denali, this species occurs along rivers and terraces in the northern half of the Park.
The average elevation of a site is 505 meters, the majority of specimens occurring between 400-800 meters. The average site incline is 4.6 degrees. Those few plants found on higher slopes were found on southern aspects.