in botany, a genus of the triandria digynia clas. The calyx consists of two valves, and the florets are thick and downy. There are six species of arundo, four of which are natives of Britain, viz., the phragmitis, or common red-grass; the calamagrostis, or branched red-grass; the epigejos, or small red-grass; and the arenaria, or sea red-grass.