ARENARIA, or SANDWORT, in botany: A genus of the decandria trigynia class; and in the natural method ranking under the 22d order, Caryophyllæ. The calyx has five open leaves; the petals are five, and entire; the capsule is unilocular, and contains many seeds. There are 17 species of arenaria, only seven of which are natives of Britain, viz. the peploides, or sandwort; the trinervis, or plantain-leaved sandwort; the serpylli-folia, or least sandwort; the saxatilis, or mountain-sandwort; the laricifolia, or larch-leaved sandwort; the tenuifolia, or fine-leaved sandwort; and the rubra, or purple-flowered sandwort.