Silene williamsii is a perennial herb in the pink family (Caryophyllaceae) that is endemic to Alaska and the Yukon Territory and occurs in floodplains and dry slopes in the northern foothills of Denali. This species has notched petals and a green, urn-shaped calyx, and is covered with sticky-viscid glands that make it easy to recognize. Plants grow 5-30 cm tall from a branched rootstock. Leaves are mostly attached to the stem, oppositely arranged, lanceolate, and hairy on both sides. The stems are much-branching and with sticky, glandular hairs. The flowers are arranged in a terminal cyme. Sepals are fused into an urn-shaped calyx 12 mm long. Petals are white and notched, shorter than the calyx. The fruit is a light brown capsule containing many red-brown seeds. This plant can be distinguished from other species of Silene in Denali by its much branched habit, the fact that the plant is sticky due to viscid glands, and its large, green, urn-shaped calyx.
Silene williamsii typically flower mid-June to July.
S. williamsii is monoecious and insect pollinated. Seeds have no special adaptation for dispersal and are likely wind and gravity disseminated.
Silene williamsii is endemic to Alaska and adjacent areas including Yukon Territory. In Alaska, this species only occurs in the mountains of the eastern and central interior (mostly south of the Yukon River). In Denali, this species occurs in the northeastern corner of the park.
S. williamsii is found growing in the park at elevation from 275 m to 978 m with an average site elevation of 633 m. This species is more commonly seen on south-facing slopes. It prefers steep slopes with an average site slope angle of 15 degrees.