Sea buckthorn is the small, vivid orange, oval berry that crowds in dense clusters along the thorny, silver-leaved branches of a tough shrub of coastal dunes and cold mountain Eurasia. Mouth-puckeringly sour and astringent with a startling tropical tang of mango, passion fruit and citrus, it is almost never eaten raw by the handful; instead it is pressed into juice, puree, syrup and a prized orange oil, and it ranks among the richest fruit sources of vitamin C and carotenoids known.