General: Perennial herb from a simple or branched stem-base; stems erect, several, branched above, long woolly-hairy and more or less glandular-hairy, 20-60 cm tall.
Leaves: Basal leaves few, soon deciduous; stem leaves opposite, 4-7 pairs, oblanceolate below to lanceolate above, long woolly-hairy and more or less glandular-hairy, 6-7 cm long, 0.5-1.5 cm wide, unstalked and slightly fused; stipules lacking.
Flowers: Inflorescence of several to many flowers in a leafy and usually compact cluster; petals 5, white, stalklike at the bases, the stalks about 15 mm long, the blades very short, egg-shaped, about 2 mm long, entire or shallowly notched at the tip, the appendages 4 (5-6); sepals 5, united, forming a tube about 15 mm long at flowering time, becoming more nearly club- or bell-shaped in fruit, 10-nerved.
Fruits: Capsules oblong, 1-celled; seeds light brown, 2.0 mm long, corrugate-wrinkled and inflated.
Silene scouleri is also glandular and has white flowers, but the blades of the petals are 6-7 mm long and deeply lobed, in contrast to those of Silene spaldingii which are only 2 mm long and unlobed or only shallowly notched. The stem leaves of S. scouleri are strongly reduced upwards, and the lower leaves exceed 7.5 cm and are long-tapering with an narrowly acute apex. In contrast, the stem leaves of S. spaldingii are only weakly reduced upwards, longer than 7.5 cm, and broadly lanceolate.
