Grevillea robusta

{{Short description|Species of shrub in the family Proteaceae endemic to eastern Australia}}

{{Speciesbox

|name = Silky oak

|image = Grevillea robusta flowering in Gan Shmuel01.jpg

|image_caption = In flower in Israel

|genus = Grevillea

|species = robusta

|authority = A.Cunn. ex R.Br.

}}

Image:Silky Oak (Grevillea robusta) JCB.jpg

File:銀樺 Grevillea robusta 20210411185712.jpg

Grevillea robusta, commonly known as the southern silky oak, silk oak or silky oak, silver oak or Australian silver oak,{{cite web |title=Grevillea robusta |url=https://keyserver.lucidcentral.org/weeds/data/media/Html/grevillea_robusta.htm |publisher=Queensland Government |access-date=19 June 2018}} 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 {{convert|5-40|m|ft|sigfig=1|abbr=on}} tall. The bark is dark grey and furrowed. Its leaves are fern-like, {{convert|10-34|cm|in|sigfig=1|abbr=on}} long, {{convert|9-15|cm|in|sigfig=1|abbr=on}} 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, {{convert|12-15|cm|in|sigfig=1|abbr=on}} long. The carpel (the female part) of each flower has a stalk {{convert|21-28|mm|in|sigfig=1|abbr=on}} 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.{{cite web |last1=Makinson |first1=Robert O. |title=Grevillea robusta |url=http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Grevillea~robusta |publisher=Royal Botanic Garden Sydney |access-date=19 June 2018}}{{cite book|title=RHS A-Z encyclopedia of garden plants|year=2008|publisher=Dorling Kindersley|location=United Kingdom|isbn=978-1405332965|pages=1136}}

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Grevillea robusta was first formally described in 1830 by Robert Brown after an unpublished description by Allan Cunningham.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.{{cite web|title=Grevillea robusta|url= https://id.biodiversity.org.au/instance/apni/457154|publisher=APNI|access-date=20 June 2018}}{{cite book |last1=Brown |first1=Robert |title=Supplementum primum Prodromi florae Novae Hollandiae |date=1830 |location=London |page=24 |url=https://www.biodiversitylibrary.org/item/77294#page/538/mode/1up |access-date=19 June 2018}} The specific epithet (robusta) is a Latin word meaning "strong like oak" or "robust".{{cite book|author-link1=Roland W. Brown|last1=Brown|first1=Roland Wilbur|title=The Composition of Scientific Words|date=1956|publisher=Smithsonian Institution Press|location=Washington, D.C.|page = 556}}

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.{{cite web |title=Grevillea robusta |url=https://apps.lucidcentral.org/rainforest/text/entities/grevillea_robusta.htm |author=F.A. Zich |author2=B.P.M Hyland |author3=T. Whiffen |author4=R.A. Kerrigan |website=Australian Tropical Rainforest Plants, Edition 8 |year=2020 |publisher=Commonwealth Scientific and Industrial Research Organisation (CSIRO) |access-date=2 March 2021}}

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.{{cite web |title=Grevillea robusta |date=3 July 2020 |url=https://www.nationalarboretum.act.gov.au/living-collections/forests-and-trees/forest-51 |publisher=National Arboretum Canberra |access-date=24 June 2024}}

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.{{Cite book |last=Leiper |first=Glen |title=Muteroo: Plant use by Australian Aboriginal People. |publisher=Eagleby South State School |location=Brisbane}}{{Cite book |last=Welsby |first=Thomas |title=Recollections of the Natives of Moreton Bay. |publisher=University Society (Brisbane) |year=1916}}

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 {{convert|-8|C|F|abbr=on}}.{{cite web |title=Silkoak (Robusta) |url=http://www.gardenguides.com/taxonomy/silkoak-grevillea-robusta/ |website=Garden Guides |publisher=Leaf Group |access-date=2019-05-02 |archive-url=https://web.archive.org/web/20110716071716/http://www.gardenguides.com/taxonomy/silkoak-grevillea-robusta/ |archive-date=2011-07-16}} 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.{{cite web |title=Grevillea robusta (silky oak) |url=https://www.cabi.org/isc/datasheet/25866 |website=Invasive Species Compendium |publisher=CAB International |access-date=2019-05-02}}

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,[http://www.rainforestinfo.org.au/good_wood/os_ozsp.htm Overseas-grown Australian Timber Species] Retrieved on 8 December 2008 and can also be grown alongside maize in agroforestry systems.{{Cite journal| last1 = Jackson | first1 = N.| title = Tree pruning as a means of controlling water use in an agroforestry system in Kenya| journal = Forest Ecology and Management| volume = 126| issue = 2| pages = 133–152| year = 2000| doi = 10.1016/S0378-1127(99)00096-1}}

In the UK, G. robusta has gained the Royal Horticultural Society's Award of Garden Merit.{{cite web|title=Grevillea robusta AGM|url= https://www.rhs.org.uk/Plants/8114/Grevillea-robusta/Details |work=RHS Plant Finder|publisher=Royal Horticultural Society|access-date=15 July 2020}}{{cite web | url= https://www.rhs.org.uk/plants/pdfs/agm-lists/agm-ornamentals.pdf | title = AGM Plants - Ornamental | date = July 2017 | page = 43 | publisher = Royal Horticultural Society | access-date = 3 March 2018}}

Toxicity and allergic reactions

The flowers and fruit contain toxic hydrogen cyanide.Everist, S.L., Poisonous Plants of Australia, Angus & Robertson, 1974. 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