Silky Oak

Grevillea robusta

A tree with an odd-looking flower

If you’re not from Australia, you may never have seen a flower quite like that of the silky oak. Like many of the Australian plants in the Proteaceae family, its flowers don’t have a typical flower shape. While they usually all have the same components (sepals, petals, stamen, stigma), they are twisted around just like some elaborate orchids are twisted to serve their purpose. In the silky oak, the top of the stamen is contained within one of the petals. The result is an odd loop that forms from this twisted arrangement.


Native originally to Australia, the silky oak was planted around the world in reforestation projects. In Hawaii for example it was introduced in 1859. From about 1919 to 1959 nearly 2.2 million trees were planted around the islands. But, unlike other Hawaiian invaders, the tree doesn’t seem to invade or spread rapidly. It has been a pest in some places of the Big Island, but is a relatively low threat.

It grows on dry to somewhat mesic slopes where it does quite well.

General Description

Silky oak, Grevillea robusta, is a medium to fairly large tree with light gray, rouge, bark with mainly closely spaced furrows. The trunk tends to be straight and tall. Flowers form on the plant in season (in Hawaii, April and May) and extend through the summer. Flowers are striking, abundant, and yellow to orange. Leaves are distinctive and feathery. From a distance they can have a silvery look to them. This is a result of a silvery underside which contrasts the dark green surface. These leaves, which can be six to twelve inches long, alternate along the stem. The leaves are compound with paired leaflets arranged along the central stem. Unlike most compound leaves, these leaflets are deeply lobed with sharp points on the ends. This makes is look almost fernlike.

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Written by Rob Nelson

Rob is an ecologist from the University of Hawaii. He is the co-creator and director of Untamed Science. His goal is to create videos and content that are entertaining, accurate, and educational. When he's not making science content, he races whitewater kayaks and works on Stone Age Man.

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