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Sea spurge is a long-lived herbaceous coastal plant native to Africa, temperate Asia, and many parts of Europe, and is invasive in Australia. The plant is fleshy and glaucous (bluish grey/green), with stalks that turn reddish brown with age, and grows up to 70cm tall. The stems contain a milky sap that is toxic to people and animals. Leaves are obovate-oblong at the base to ovate at the top of the stems and are approximately 5-20mm long and 2-15mm in width. The leaves are crowded and overlapping on stems that branch from a woody base, and divide into 3-5 flowering branches. It produces a cluster of cup-shaped flower heads on a distinct stalk. Flowers are cyathia ('fake' flowers) consisting of a female flower surrounded by male flowers (reduced to stamen) and four crescent-shaped glands that contain nectar to attract pollinators. Flowers are surrounded by a pair of bracts (modified leaf or scale) measuring approximately 1.5mm long. Capsule-like fruit are produced containing three large seeds that are buoyant and can be carried vast distances by ocean currents. Sea spurge grows from deep tap-roots.
The species forms dense infestations in coastal, open sand areas and around beach debris, from the high water flotsam line into the dunes. It is most likely to be found on the west coast of the north and south islands of New Zealand due to seed transferral from Australia, but there is also the possibility of currents moving seeds to northeastern beaches. The New Zealand climate is similar to that of the species native habitat and is not thought to be a barrier to establishment.