Arenaria congesta is a species of flowering plant in the pink family known by the common name ballhead sandwort. It is native to western North America from central Canada to the American southwest. This is a perennial herb forming a tuft of slender upright stems up to about 40 centimeters tall. The leaves are needlelike to thready, up to 8 centimeters long and only a few millimeters wide. They may be fleshy or flat and they often have a very sharp tip. Most of the leaves are located in a patch at the base of the plant, and there are a few scattered along the mostly naked stem. The flower cluster is an open or rounded cyme of five-petalled white flowers. The fruit is a toothed capsule containing several reddish seeds. The plant was used for a variety of medicinal purposes by Native American groups, including the Shoshone.