单叶蔓荆（学名：Vitex rotundifolia），又名蔓荆子、海埔姜、白埔姜、山埔姜，是马鞭草科牡荆属的一种多年生藤状植物，其根茎可以匍匐生长，尤喜沙地。单叶蔓荆夏季开花，秋季结果。果实呈圆形成串，每串少则几粒，多则几十粒。果为核果，成熟时会转为黑色。蔓荆子味清香，民间有治疗头疼、失眠的功效，人们常用蔓荆子装枕头。

喜爱生长于海岸沙地，为海岸定砂之优良植物。生长于**全岛、离岛、澎湖、小琉球、绿岛、兰屿。分布中国、韩国、日本、琉球、菲律宾、印度。

除了**本岛，在龟山岛还可以看到其他地方不易看到的白花种。 另外，它与三叶蔓荆（学名：Vitex trifolial）极为相似，最大的不同在于三叶蔓荆的叶子为三出复叶，但是有时候也会杂有单叶，主要分布**中部沿海地区。

Vitex rotundifolia, the roundleaf chastetree or beach vitex is a species of Vitex that 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 woody perennial plant 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.