Grevillea robusta A.Cunn. ex R.Br.

Kew Species Profiles

General Description

Silky oak is one of the finest flowering trees from Australia, with fern-like leaves and rich yellow, comb-like flowers in late spring.

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.

Species Profile

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.

Description

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.

Uses

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)

Cultivation

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.

Distribution

Australia

Ecology

Rainforest.

Conservation

Not threatened.

Hazards

The leaves are poisonous and can cause skin irritation. Cases of severe dermatitis are rare, but have been reported.

Distribution

Biogeografic region: Andean. Elevation range: 1500–1500 m a.s.l. Cultivated in Colombia. Colombian departments: Antioquia, Bogotá DC, Tolima.

Habit

Tree.

Conservation

IUCN Red List Assessment (2021): LC.

Ecology

Habitat according IUCN Habitats Classification: forest and woodland, shrubland, artificial - terrestrial.

Bernal, R., Gradstein, S.R. & Celis, M. (eds.). 2015. Catálogo de plantas y líquenes de Colombia. Instituto de Ciencias Naturales, Universidad Nacional de Colombia, Bogotá. http://catalogoplantasdecolombia.unal.edu.co

Distribution

Cultivada en Colombia; Alt. 1500 m.; Andes.

Morphology General Habit

Árbol

IUCN Red List of Threatened Species https://www.iucnredlist.org/species/61956847/61956849

Conservation

LC - least concern

Extinction risk predictions for the world's flowering plants to support their conservation (2024). Bachman, S.P., Brown, M.J.M., Leão, T.C.C., Lughadha, E.N., Walker, B.E. https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.19592

Conservation

Predicted extinction risk: not threatened. Confidence: confident

Proteaceae, R.K. Brummitt & Serena K. Marner. Flora of Tropical East Africa. 1993

Morphology General Habit

Tree up to 30 m. high.

Morphology Leaves

Leaves up to 35 cm. long, pinnate with up to 22 alternate or subopposite pinnae, the pinnae with 1-several linear or linear-oblong acute lobes to deeply pinnatifid or pinnate with up to 16 lobes or pinnules, glabrous above, closely appressed pubescent beneath.

Morphology Reproductive morphology Inflorescences

Inflorescence with main axis up to 24 cm. long, usually with several simple lateral branches from near the base, appressed pubescent towards the base but glabrous distally; pedicels 9-15 mm. long, glabrous.

Morphology Reproductive morphology Flowers Perianth

Perianth 7-10 mm., glabrous, bright yellow to orange or reddish.

Morphology Reproductive morphology Fruits

Fruits ±15 ×10 mm., blackish, glabrous.

Habitat

Sometimes more or less established in native vegetation near habitation or roadsides; recorded 1500-2000 m. but probably planted more widely

Distribution

Native of Australia (Queensland and New South Wales), where it is confusingly known as Silky Oak, now cultivated widely in tropical countries

Bernal, R., G. Galeano, A. Rodríguez, H. Sarmiento y M. Gutiérrez. 2017. Nombres Comunes de las Plantas de Colombia. http://www.biovirtual.unal.edu.co/nombrescomunes/

Vernacular

árbol de seda, rabo de pavo, roble australiano

Use Animal Food

Used as animal food.

Use Environmental

Environmental uses.

Use Fuel

Used for fuels.

Use Gene Sources

Used as gene sources.

Use Food

Used for food.

Use Invertebrate Food

Used as invertebrate food.

Use Materials

Used as material.

Use Medicines

Medical uses.

Use Poisons

Poisons.