Vitex rotundifolia, the roundleaf chastetree or beach vitex, is a species of flowering plant in the sage family Lamiaceae. It is native to seashores throughout the Pacific. Its range includes continents and islands stretching from India east to Hawaii and from Korea south to Australia. This shrub typically grows approximately 1 m in height. It has a sprawling growth habit and produces runners that root regularly at nodes. This rooting pattern allows the plant to spread rapidly. At maturity, V. rotundifolia produces blue-purple flowers that are borne in clusters and ultimately yield small brown-black fruits. Its leaves are rounded at the tips with green upper surfaces and silver lower surfaces. While the plant is a seashore obligate, it grows over a wide latitude range. It has been used for medicinal purposes throughout its native range. More recently, it was imported to the eastern United States where it has become a seashore invasive. Control efforts are presently underway to protect the fragile beach dune ecosystem. Description Vitex rotundifolia is a sprawling shrub that can grow as tall as 1.5 m though it typically ranges from 0.5 to 1 m in height. As a product of its rapid nodal rooting, the plant can form dense mats reaching in excess of 10 m from the parent plant. Stems New stems are green, square and fleshy initially before maturing brown and woody. Older, large-diameter stems are covered with heavily fissured bark. Running horizontal stems produce frequent upright branches. Leaves are strongly aromatic, intensifying when crushed. Leaves The majority of leaves are simple, but they can occasionally be palmate trifoliate or 2-leaved. Leaves measure 2 to 6.5 cm in length and 1–4.5 cm in width. Leaf margins are entire. The leaf shape varies from ovate to obovate with acute bases and obtuse apices. Occasionally, leaf apexes are acute or emarginate. Upper leaf surfaces are dark green whereas lower leaf surfaces range in color from silver to white to light green; all leaf surfaces are tomentose. Petiole bases are typically somewhat purple and measure 0 to 1 cm in length. Blades are cupped downward slightly. Leaf veins are lighter green than surrounding tissue. Flowers The flowers are borne in indeterminate panicles that may be terminal or axillary. Infloresences measure 3 to 7 cm in length. The calyx is cup-shaped and 4 to 4.5 cm long. Flowers are zygomorphic, purple to blue-purple, and short pedunculate. They are