 A. brownii is the only endemic species of Hawaiian Amaranthus in the Hawaiian Islands. It is an herbaceous annual plant that grows to a height of 30 – 90 cm (0.98 – 2.95 ft) and has narrow, linear leaves, small green flowers, and fruit that holds a single, dark red seed. A. brownii is monoecious; that is, the male and female flowers are found together on the same plant. It differs from other Hawaiian species of Amaranthus with its spineless leaf axils, linear leaves, and indehiscent fruits (fruit which does not open to release seeds when ripe). The fruits are ovoid and between 0.8 – 1 mm long and 0.6 – 0.8 mm wide. The plant is thought to be anemophilous (pollinated by wind).
