henna tree, (Lawsonia inermis), tropical shrub or small tree of the loosestrife family (Lythraceae), native to northern Africa, Asia, and Australia. The leaves are the source of a reddish-brown dye, known as henna, which is commonly used for temporary body art and to dye fabrics. The plant bears small opposite leaves and small, fragrant, white to red flowers. In addition to being grown for its dye, it is used as an ornamental.