Grevillea robusta (silky oak)
Grevillea robusta in Yunnan (Photo: Martyn Rix)
Grevillea robusta A.Cunn. ex R.Br.
silky oak, Australian silky oak
Ornamental, shade tree, timber for furniture.
The leaves are poisonous and can cause skin irritation. Cases of severe dermatitis are rare, but have been reported.
About this species
Grevillea robusta was first described in 1830 by Allan Cunningham, who was employed by the Superintendent of Kew, William T. Aiton, to write Hortus Kewensis and was then sent by Kew to collect plants in Brazil, Australia and New Zealand. Allan succeeded his brother Richard as Superintendent of the Botanic Garden in Sydney in 1836. In subtropical areas silky oak forms a large upright tree, with spreading lower branches. Its flowers, which open from October to December, are rich in nectar and attract birds and fruit bats. The seedlings, with their ferny foliage and silky new growth, make attractive houseplants.
Geography and distribution
Native to Australia, silky oak is found in the rainforests of south-eastern Queensland and north-eastern New South Wales. It has been planted throughout the tropics and subtropics as a shade tree and in agroforestry, and has become naturalised in many countries. In some places, such as Hawaii, parts of Australia, Mauritius, and Brazil, it has become invasive, out-competing native vegetation.
Silky oak is a tall, upright tree measuring up to 30 m tall (although most commonly reaching around 10 m). Its bark is greyish and deeply grooved. Its leaves are much divided, and are dark green above, silky and silvery beneath, measuring 15-30 cm long. The leaves are rather leathery in texture. The flowers are bright orange-yellow, and are held horizontally in crowded racemes 10-15 cm long, each with a conspicuous, upright, cone-shaped pollen-presenter. The fruits are flattened, 15-20 mm long, with a persistent style and one or two brown seeds, each with a narrow wing surrounding it.
Illustration from Curtis's Botanical Magazine
Curtis’s Botanical Magazine (Editor: Martyn Rix) provides an international forum of particular interest to botanists and horticulturists, plant ecologists and those with a special interest in botanical illustration.
Now well over 200 years old, the Magazine is the longest running botanical periodical featuring colour illustrations of plants. Each four-part volume contains 24 plant portraits reproduced from watercolour originals by leading international botanical artists. Detailed but accessible articles combine horticultural and botanical information, history, conservation and economic uses of the plants described.
Published for the Royal Botanic Gardens, Kew by Blackwell Publishing.
Grevillea robusta is commonly planted as a shade tree or street tree in tropical and subtropical areas. Its timber is used for making furniture, and in Sri Lanka and East Africa the tree is planted as a fuelwood species.
It is fast-growing, drought-resistant and tolerant of poor soil, so has been used for reclamation of deforested land in Africa and America. However, its leaves produce allelopathic compounds which inhibit the establishment of other plants (including native species), and in some places, such as Hawaii, silky oak is invasive and considered a serious weed.
In China, South India and Sri Lanka it has often been planted to provide shade in tea plantations, and in Brazil, India and Hawaii for shade in coffee plantations.
Young plants are grown for their foliage, and make attractive indoor plants, or greenhouse plants in temperate climates. In warmer climates the resulting trees are too large for most urban gardens. The flowers, which are produced in large quantities following a dry winter and spring, are rich in nectar and attract birds and insects, as well as fruit bats. The cut leaves are used in floristry.
Millennium Seed Bank: Seed storage
Kew's Millennium Seed Bank Partnership aims to save plant life world wide, focusing on plants under threat and those likely to be of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.
Description of seeds: Average 1,000 seed weight = 20 g
Number of seed collections stored in the Millennium Seed Bank: One
Seed storage behaviour: Orthodox (the seeds of this plant survive drying without significant reduction in their viability, and are therefore amenable to long-term frozen storage such as at the MSB)
Silky oak is easy to grow in subtropical areas, surviving even in poor and degraded soils. In cold areas it is easily grown as a seedling, in a large pot of sandy soil, with the stem trained up a slender cane. In winter, the plant should be given as much light as possible, and kept rather dry. The leaves would probably survive a few degrees of overnight frost. Propagation is best by seed.
This species at Kew
Samples of wood, bark and gum from Grevillea robusta are held in the behind-the-scenes Economic Botany Collection at Kew, where they are made available to researchers by appointment.
Desmond, R. (1977). Dictionary of British and Irish Horticulturists. Taylor and Francis Ltd, London.
Elliot, W.D. & Jones, D.L. (1990). Encyclopedia of Australian Plants Suitable for Cultivation, Volume 5. Lothian, Melbourne, Sydney, Auckland.
IUCN Invasive Species Specialist Group, Global Invasive Species Database. Available online.
Kew Science Editor: Martyn Rix
Kew contributors: Steve Davis (Sustainable Uses Group)
Copyediting: Emma Tredwell
While every effort has been taken to ensure that the information contained in these pages is reliable and complete, the notes on hazards, edibility and suchlike included here are recorded information and do not constitute recommendations. No responsibility will be taken for readers’ own actions.