Grevillea robusta, commonly known as the southern silky oak, silk oak or silky oak, silver oak or Australian silver oak, is a flowering plant in the family Proteaceae. It is a tree, the largest species in its genus but is not closely related to the true oaks, Quercus. It is a native of eastern coastal Australia, growing in riverine, subtropical and dry rainforest environments.
Grevillea robusta is a fast-growing evergreen tree with a single main trunk, growing to 5–40 m (20–100 ft) tall. The bark is dark grey and furrowed. Its leaves are fern-like, 10–34 cm (4–10 in) long, 9–15 cm (4–6 in) wide and divided with between 11 and 31 main lobes. Each lobe is sometimes further divided into as many as four, each one linear to narrow triangular in shape. It loses many of its leaves just before flowering.
The flowers are arranged in one-sided, "toothbrush"-like groups, sometimes branched, 12–15 cm (5–6 in) long. The carpel (the female part) of each flower has a stalk 21–28 mm (0.8–1 in) long. The flowers are glabrous and mostly yellowish orange, or sometimes reddish. Flowering occurs from September to November and the fruit that follows is a glabrous follicle.Grevillea robusta is a deciduous tree with a dense, conical crown; it can grow 12 - 25 metres tall with exceptional specimens up to 40 metres.The bole, which can be 80 - 120cm in diameter, is straight, unbuttressed, and can be free of branches for up to 15 metres.
The tree is often cultivated in the tropics for timber and as a windbreak. It is a very ornamental plant, valued especially for its attractive fern-like foliage and brilliant orange floral display; it is often grown in gardens and as a street tree. The tree flowers freely in subtropical areas, but only poorly in the lowland tropics.