ARENARIA, or chickweed, in botany, a genus of the decandria trigynia class. The calix has five open leaves; the petals are five, and entire; the capsule is unifocular, and contains many seeds. There are 17 species of arenaria, only 7 of which are natives of Britain, viz. the peploides, or sea-chickweed; the trinervia, or plantain-leaved chickweed; the serpyllifolia, or least chickweed; the faxatilis, or mountain-chickweed; the laricifolia, or larch-leaved chickweed; the tenuifolia, or fine-leaved chickweed; and the rubra, or purple-flowered chickweed.