Silver Oak

''Grevillea robusta'', commonly known as the southern silky oak, silk oak or silky oak, silver oak or Australian silver oak, is a species of flowering plant in the family Proteaceae. Despite its common names, it is unrelated to true oaks, which belong to the family Fagaceae. ''Grevillea robusta'' is a tree, and is the largest species in its genus. It is a native of eastern coastal Australia, growing in riverine, subtropical and dry rainforest environments.

Description

''Grevillea robusta'' is a fast-growing evergreen tree with a single main trunk, growing to tall. The bark is dark grey and furrowed. Its leaves are fern-like, long, 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, long. The carpel (the female part) of each flower has a stalk 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.

Taxonomy and naming

''Grevillea robusta'' was first formally described in 1830 by Robert Brown after an unpublished description by Allan Cunningham. The type specimen was collected by Cunningham on the eastern edge of Moreton Bay in 1827. Brown's description was published in '' Supplementum primum Prodromi florae Novae Hollandiae''. The specific epithet (''robusta'') is a Latin word meaning "strong like oak" or "robust".

Distribution and habitat

Silky oak occurs naturally on the coast and ranges in southern Queensland and in New South Wales as far south as Coffs Harbour where it grows in subtropical rainforest, dry rainforest and wet forests. It is now relatively rare in its natural habitat but has been widely planted. It has become naturalised in many places, including on Norfolk Island, Lord Howe Island and the Atherton Tableland in Australia, and overseas in South Africa, New Zealand, Hawaii, French Polynesia, Jamaica and Florida. It is regarded as a weed in parts of New South Wales and Victoria, and as invasive in Hawaii and South Africa.

Uses

Before the advent of aluminium, ''Grevillea robusta'' timber was widely used for external window joinery, as it is resistant to wood rot. It has been used in the manufacture of furniture, cabinetry, and fences. Owing to declining ''G. robusta'' populations, felling has been restricted.

The flowers of ''Grevillea robusta'' produce a rich nectar, which Indigenous Australians traditionally consumed either directly from the blossom or by shaking the nectar into water.

Cultivation

When young, it can be grown as a houseplant where it can tolerate light shade, but it prefers full sun because it grows best in warm zones. If planted outside, young trees need protection on frosty nights. Once established, it is hardier and tolerates temperatures down to . It needs occasional water but is otherwise fairly drought-resistant. Care needs to be taken when planting it near bushland because it can be invasive.

''G. robusta'' is often used as stock for grafting difficult-to-grow grevilleas. It has been planted widely throughout the city of Kunming in south-western China, forming shady avenues.

''G. robusta'' is grown in plantations in South Africa, and can also be grown alongside maize in agroforestry systems.

In the UK, ''G. robusta'' has gained the Royal Horticultural Society's Award of Garden Merit.

Toxicity and allergic reactions

The flowers and fruit contain toxic hydrogen cyanide. Tridecylresorcinol in ''G.robusta'' is responsible for contact dermatitis.Menz, J., Rossi, R., Taylor, W.C, Wall, L., Contact dermatitis from Grevillea " Robyn Gordon", ''Contact Dermatitis'', Vol. 15, Iss. 3, pp 126-131, Apr 2006

Image:Silveroak.jpg, silky oaks planted in a tea plantation
Image:Grevillea robusta trunk bark 01.jpg, trunk bark
Image:Grevillea robusta leaf 01.jpg, leaf
Image:Grevillea robusta_flowering_05.jpg, flowering branches
Image:Grevillea robusta_flowers_01.jpg, flowers
Image:Grevillea robusta_unripe_seed_pods_01.jpg, unripe seed pods
Image:Grevillea robusta leaves and dry seed pods.jpg, leaves and dry seed pods
Image:Grevillea robusta dry seed pod.jpg, dry seed pod
Image:Grevillea robusta_seeds_01.JPG, seed pod and seeds
Image:Grevillea_Robusta.jpg, Flowering branches
Image:Grevillearobusta40181608300 6dbb4fe9b0 o.jpg, seed pods
Image:Flowers, robusta.jpg, branch end with inflorescence
Image:A tree of Koubilla (Grevillea robusta) species growing inside the Kangla fort in Imphal, Kangleipak (Manipur).jpg, Tree in Kangla Fort

References

External links

Plants of Hawaii (images): ''Grevillea robusta''

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robusta
Trees of Australia
Proteales of Australia
Flora of New South Wales
Flora of Queensland
Garden plants of Australia
Ornamental trees
Drought-tolerant trees
Plants described in 1830