Big-leaved sandwort is a low (5-20 cm tall) understory species in moist forests. It is a rhizomatous perennial that forms loose mats. The leaves are opposite and narrowly lance-shaped. The flowers are small with 5 pointy-tipped sepals and 5 white petals about the same length as the sepals. This species has also been called Arenaria macrophylla, and there are 7 additional species of Arenaria that can be found in western Washington.