Streblus smithii is endemic to the Three Kings Islands north of New Zealand. A small tree up to 5 m tall with a spread of up to 4m. It has leathery >16 cm long leaves with smooth margins. The bright green leaves are attached alternately along the stem. The lower surface of the leaf is slightly paler and has prominent veins.

A pair of long tapering stipules is found on either side of each leaf stalk. The small unisexual flowers are crowded into 5-12 cm long spikes. The female flower consists of 4, green-purple hair-covered tepals surrounding an ovary with two feathery stigmas at its top. After flowering small red and fleshy fruits (drupe), 8-9 mm in diameter is formed. The bark exudes a thick white (milk-like) sap when cut hence its common names.