King's sandwort is a small perennial with numerous slender rhizomes which forms loose mats or patches of plants up to 20 cm in diameter. The herbage of the lower stems is glabrous to minutely haired and lightly glandular on the upper stems and amidst the inflorescence. The erect flowering stems rise from 10-30 cm high. The numerous basal leaves are all narrowly linear, erect or ascending, and somewhat recurved. The basal leaves measure 2-4 cm long and from 0.5-1 mm wide. The individual leaves are somewhat flexible and soft in texture (not sharp as in Arenaria aculeata). The 2-4 pairs of stem leaves are about half as long to as long as the basal leaves.
The flowers are found in small, open cymes at the terminus of the stems. The sepals are broadly lanceolate or narrowly ovatein shape with acute to accuminat tips. They range from 3.5-6 mm long. The sepals are also somewhat membranous-margined and purplish in color. The 5 white petals range from 1.5-2 times longer than the sepals and are entire to three-cleft at the tip. The 10 ascending to spreading stamens are about as long as the petals and bear reddish to brownish anthers at their tips. The pistil typically bears 3 short styles.
Prickly Sandwort (Arenaria aculeata): The sepals are ovate in shape and obtusely- or shortly acute-tipped. Typically has shorter lower leaves less than 2 cm long that are sharp-tipped with the 2-4 pairs of stem leaves short, typically less than one-half the length of the lower leaves.
Mountain Sandwort (Arenaria capillaris): The sepals are ovate in shape and obtusely- or shortly acute-tipped. Typically has lower leaves longer than 2 cm in length, softer in texture at the tips with the 2-4 pairs of stem leaves over one-half the length of the lower leaves.
King's sandwort may be found from the sagebrush foothills to the rocky slopes at timberline in the mountains.
King's sandwort may be found from southeastern Oregon east to central Idaho and south to east-central California. In Oregon it may be found from western Lake County east to northern Malheur County.