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Overview

Brief Summary

Proteaceae -- Protea family

    Roger G. Skolmen

    Silk-oak (Grevillea robusta), also often called silver-oak, is a  medium to large tree commonly planted as an ornamental in many  warm-temperate and semitropical climates. It has been established as a  forest tree in some countries and shows promise as a fast-growing timber  tree.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Roger G. Skolmen

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Comprehensive Description

Miscellaneous Details

"Notes: Plains to High Altitude, Cultivated, Native of Australia"
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Brief

Flowering class: Dicot Habit: Tree Distribution notes: Exotic
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Description

Large semi-deciduous tree. Leaves pinnately compound with deeply lobed leaflets, dark green above, silvery-grey below. The flowers are borne in horizontal, one-sided, brush-like inflorescences, orange-yellow.
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Derivation of specific name

robusta: robust
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Distribution

National Distribution

United States

Origin: Exotic

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

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"Native of Australia, widely cultivated as a shade tree in the hilly areas."
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"
Global Distribution

Native of East Australia; now common in tropics and subtropics

Indian distribution

State - Kerala, District/s: All Districts

"
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"Maharashtra: Ahemdnagar, Dhule, Kolhapur, Satara, Sindhudurg Karnataka: Chikmagalur, Hassan, Mysore Kerala: All districts Tamil Nadu: All districts"
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Silk-oak is native to coastal eastern Australia from the Clarence River,  New South Wales, to Maryborough, Queensland, and is now naturalized in  Hawaii and southern Florida (3,16). It was introduced into Hawaii about  1880 and is found on all islands where it reproduces prolifically in  certain leeward grassland locations. Although a nongregarious tree in its  native habitat, it grows well in pure plantations in Hawaii (18). It is  common as an ornamental in Hawaii, Florida, California, and Puerto Rico  (5). Because of its prolific reproduction, it has been classed a noxious  weed on ranchland in Hawaii (9). In the tropical highlands of India, where  it has also been extensively planted, it is often an undesirable escapee  from cultivation (13).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Roger G. Skolmen

Source: Silvics of North America

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Worldwide distribution

Native of Australia
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Distribution:- Silver or silky oak, an endemic of E. Australia, is extensively cultivated in tropics and sub-tropics as an ornamental, road-side tree and as a shade or wind break tree in tea and coffee gardens. Cultivated throughout Pakistan since long, especially in cantonments and satellite towns. It has recently been planted in large numbers in Islamabad.
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Cultivated in Nepal and elsewhere; native of Australia.
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Physical Description

Morphology

"
Flower

In racemes on leafless stem; yellow to orange. Flowering from November-December.

Fruit

Boat-shaped follicles, woody; seeds 2, winged. Fruiting December onwards.

Field tips

Bark grey, rough, irregular and deeply fissured.

Leaf Arrangement

Alternate-distichous

Leaf Type

2-pinnatifid

Leaf Shape

Lanceolate

Leaf Apex

Acute

Leaf Base

Cuneate

Leaf Margin

Entire

"
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Description

A handsomely straight evergreen tree, 10-25 m tall. Leaves 15-33 cm long; leaflets 7-19, 3-12 cm long, sessile, entire or pinnatifid, olive green above, silver grey silky hairy beneath; margin recurved. Racemes 5-15 cm long, appearing on the old wood, solitary, 2 or a few forming a panicle. Flowers solitary, in twos or threes; pedicel 1-1.5 cm long, glabrous, leaving a permanent white lenticular scar. Sepals 1.5-2 cm long, hooded, at first all fused together except on one side, later on fused in twos basally and apically, free for the greater length in the middle, these pairs in their turn free from each other or slightly fused above, orange yellow to orange or golden yellow to lemon yellow with dark red inner base. Stamens sessile; connective not produced beyond the anther cells; anthers about 1 mm long. Disc semi-annular. Gynophore about 2-3 mm long. Ovary glabrous; style lemon yellow, 1-2.5 cm long, dilated at the apex and bearing a greenish-yellow 1 mm long stigmatic cone. Follicle 2-seeded, 1.5-2. cm long, about 1 cm broad, silver grey to olive green, dehiscent. Seeds 1-1.5 cm long, 0.5-1 cm broad, broadly winged, thin, ovate, non-endospermic.
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Elevation Range

760-1500 m
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Diagnostic Description

Diagnostic

"Habit: A moderate-sized, handsome tree, upto 20m."
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Diagnostic

"A handsomely straight evergreen tree, 10-25 m tall. Leaves 15-33 cm long; leaflets 7-19, 3-12 cm long, sessile, entire or pinnatifid, olive green above, silver grey silky hairy beneath; margin recurved. Racemes 5-15 cm long, appearing on the old wood, solitary, 2 or a few forming a panicle. Flowers solitary, in twos or threes; pedicel 1-1.5 cm long, glabrous, leaving a permanent white lenticular scar. Sepals 1.5-2 cm long, hooded, at first all fused together except on one side, later on fused in twos basally and apically, free for the greater length in the middle, these pairs in their turn free from each other or slightly fused above, orange yellow to orange or golden yellow to lemon yellow with dark red inner base. Stamens sessile; connective not produced beyond the anther cells; anthers about 1 mm long. Disc semi-annular. Gynophore about 2-3 mm long. Ovary glabrous; style lemon yellow, 1-2.5 cm long, dilated at the apex and bearing a greenish-yellow 1 mm long stigmatic cone. Follicle 2-seeded, 1.5-2.cm long, about 1 cm broad, silver grey to olive green, dehiscent. Seeds 1-1.5 cm long, 0.5-1 cm broad, broadly winged, thin, ovate, non-endospermic."
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Diagnostic

Habit: Tree
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Ecology

Habitat

General Habitat

Grown as shade tree
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Soils and Topography

Silk-oak is tolerant of a wide range of soils if they are well drained  (16). It will grow on neutral to strongly acid soils but does best on  those that are slightly acid (2,12). In Hawaii, good growth is achieved on  soils of a wide range of orders. Silk-oak grows well on Histosols,  Inceptisols, and Ultisols. The majority of the best stands are on  Dystrandepts and Tropofolists developed on gentle to moderate slopes of  basalt lava rock or ash.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Roger G. Skolmen

Source: Silvics of North America

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Climate

In Hawaii, silk-oak has been planted extensively in both wet and dry  locations on all islands from near sea level to more than 900 in (3,000  ft) elevation (9). The mean temperature ranges from 10° to 26° C  (50° to 78° F) within this elevational range, with extremes of 4°  and 35° C (40° and 95° F). Silk-oak, for many years, was  thought to be best suited for planting in and areas because of its success  as a seedling and sapling in such areas. Later it became apparent that  frequent severe moisture stress in the dry areas (less than 760 mm [30 in]  annual rainfall) caused disease susceptibility resulting in dieback as the  trees became older. Natural reproduction, however, was sometimes excellent  in these dry locations. The largest silk-oak trees in Hawaii grow in 3050  min (120 in) winter maximum or evenly distributed annual rainfall at 610 m  (2,000 ft) elevation, but the most prolific natural reproduction coupled  with excellent growth occurs in 1780 to 2400 min (70 to 95 in) evenly  distributed annual rainfall at 460 to 670 in (1,500 to 2,000 ft)  elevation. Elsewhere than Hawaii, silk-oak is reported to be capable of  withstanding occasional light frosts but must be considered frost-tender  (16). It is also reported elsewhere to be fairly hardy to drought but  tends to die back on droughty sites at 15 to 20 years of age (2).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Roger G. Skolmen

Source: Silvics of North America

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Associations

Associated Forest Cover

Where planted in pure stands in Hawaii, silk-oak maintains its purity  with little woody competition. In naturalized stands, it grows in  association with many other tree species including the native koa (Acacia  koa), 'ohi 'a (Metrosideros collina), and introduced species  such as tropical ash (Fraxinus uhdei), jacaranda (Jacaranda  mimosifolia), molucca albizzia (Albizia falcataria), black-wattle  (Acacia decurrens), Christmas-berry (Schinus  terebinthifolius), and guava (Psidium guajava).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Roger G. Skolmen

Source: Silvics of North America

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Diseases and Parasites

Damaging Agents

The oleander pit scale, Asterolecanium  pustulans Cockerell, was so damaging in Puerto Rico that further  planting of the species was discouraged (7). Amphichaeta grevilleae  is a serious leaf spot and defoliating disease in India where it kills  young plants (14). Also in India, a serious dieback is caused by a fungus,  Corticium salmonicolor (8). No serious primary insects or diseases  of the species have been noted in Hawaii, although severe dieback,  believed caused by drought, is common on most droughty sites.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Roger G. Skolmen

Source: Silvics of North America

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General Ecology

Reaction to Competition

Silk-oak is classed as very intolerant  of shade. In Australia, seedlings do not survive beneath closed pure  stands of the species because of some substance toxic to them that is  produced by or associated with roots of the trees (18). This substance is  specific to silk-oak seedlings, causing rapid chlorosis, blackening, and  death of seedlings soon after they emerge and begin to grow. Consequently,  the tree is nongregarious in its natural habitat. The toxic substance has   not been investigated in Hawaii, but it has been observed that  reproduction is lacking within dense stands or directly beneath individual  trees.

    In Hawaii, silk-oak has been planted in mixture with numerous other  species. Two of the species it dominates when in mixture are melaleuca  (Melaleuca quinquenervia) and horsetail casuarina (Casuarina  equisetifolia). Three that grow well in mixture with it are Australian  toon (Toona ciliata var. australis), tropical ash, and  koa. Three that dominate silk-oak are Norfolk-Island-pine (Araucaria  heterophylla), saligna eucalyptus (Eucalyptus saligna), and  robusta eucalyptus (E. robusta).

    In Brazil, several spacing studies indicated that at 2 years, a spacing  of 1 by 3 in (3 by 10 ft) resulted in the best height growth, but at 6  years, 2 by 2 in (6 by 6 ft) was best, with thinning planned at age 10 or  15 (Viega 1958 as cited in 2). In Brazil, an attempt is made to maintain a  basal area of 49 to 61 m²/ha (213 to 265 ft²/acre) throughout  the life of the stand. In Hawaii, silk-oak has always been planted at a  spacing of 3 by 3 in (10 by 10 ft) and left untended. In Uganda  experiments, a number of thinnings were made at various ages, but with  little apparent effect on mean annual diameter increment (4).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Roger G. Skolmen

Source: Silvics of North America

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Rooting Habit

Silk-oak does not develop a strong taproot and  roots shallowly on sites that lack moisture stress (16). On droughty sites  it roots throughout the soil profile to depths of about 2 in (6 ft).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Roger G. Skolmen

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Life History and Behavior

Cyclicity

Flowering and fruiting: June-September
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Flower/Fruit

Fl. Per: March-April.
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Reproduction

Vegetative Reproduction

Silk-oak coppices when cut. After being  damaged by fire, a 5-year-old stand in Karnataka State, India, was cut.  One year later, 93 percent of the stumps had coppiced. After 2 years 72  percent of the stumps still retained the coppice shoots, which by then  averaged 4 m (13 ft) in height (1). As far as is known, vegetative  propagation has not been practiced with the species.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Roger G. Skolmen

Source: Silvics of North America

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Seedling Development

Germination is epigeal. Seedlings are  grown in flats or containers in nurseries. Methods vary among the  countries where silkoak is grown. In some countries 4- to 6-week-old  wildings are lifted and potted and later replanted (2). Elsewhere plants  are grown to 45-cm (18-in) heights in large baskets so that they can  compete when outplanted (12). In Hawaii, seedlings in individual  containers can be grown to a plantable size of 20 cm (8 in) height and 4  mm (0. 16 in) caliper in 12 to 14 weeks.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Roger G. Skolmen

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Seed Production and Dissemination

Silk-oak is a prolific  seeder. Seeds are about 10 mm (0.4 in) long, flattened, and surrounded by  a membranous wing. There are reported to be 64,000 to 154,000 seeds per  kilogram (29,000 to 70,000/lb). Because of their relatively large wing,  the lightweight seeds are widely disseminated by wind. Possibly because  seedfall coincides with the onset of winter rains in dry leeward rangeland  in Hawaii, regeneration is most prolific on these sites.

    The seeds, if kept at 10 percent or less moisture content, can be stored  for as long as 2 years at -7° to 3° C (20° to 38° F)  with little loss in germinability. Germination of fresh, unstratified  seeds requires about 20 days. Stratification at 3° C (38° F) for  30 days, or a 48-hour water soak, substantially increases germinative  capacity of seeds that have been stored (19).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Roger G. Skolmen

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Flowering and Fruiting

In Hawaii, silk-oak flowers from March  through October, with the peak of flowering usually in June. The perfect  yellowish orange, showy flowers are borne on 8- to 18-cm (3 to 7-in) long  racemes that occur in panicles of one to several branches (3). Trees  usually begin to flower at about 10 years. The fruit, a podlike follicle,  20 mm (0.8 in) in diameter, is slightly flattened and has a long-curved  style. The hard dark-brown to black follicle splits open in late fall to  release the one or two seeds it contains but remains on the tree up to 1  year after opening. Trees near San Jose in California have been observed  to flower, fruit, and seed at times similar to those in Hawaii.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Roger G. Skolmen

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Growth

Growth and Yield

In Hawaii, the tree usually produces a  straight, erect stem even when open-grown (15). Where subjected to drought  stress sufficiently severe to cause dieback, it forms forks and multiple  leaders. On good sites (500 m; 1,600 ft altitude; 2030 mm.; 80 in annual  rainfall), dominant trees planted at spacing of 3 by 3 m (10 by 10 ft) can  be expected to be 8 to 9 m (25 to 30 ft) tall in 5 years, 15 m (48 ft) in  10 years, and 20 m (65 ft) or more in 20 years (11). Mean annual increment  of dominants on 21 different sites in Uganda, for trees 2 to 20 years in  age, ranged from 1.3 to 3.3 cm (0.5 to 1.3 in) in diameter and from 0.5 to  3.4 m (1.7 to 11.2 ft) in height (4). This indicates that the tree is fast  growing as a sapling and pole.

    Many plots have been measured in 32- to 48-yearold silk-oak plantations  in Hawaii (11). All the plantations had been planted at 3 by 3 m (10 by 10  ft) and left untended since planting. Average d.b.h. of dominant and  codominant trees at 44 years in four of the plots was 46 cm (18 in), and  the average total height was 32 m (105 ft). The most outstanding stand, at  36 years, yielded a mean annual increment of 17.5 m/ha (1,250 fbm/acre)  (11). Typically, merchantable trees in these untended stands were 36 to 46  cm (14 to 18 in) d.b.h. with 9 to 11 m (30 to 36 ft) of branch-free stem.

    In India, trees reach 50 cm (20 in) diameter in 30 years when grown at  an initial spacing of 3 by 4 m (10 by 13 ft) and thinned once at about 5  years, and again later if needed to maintain growth rate. Such stands  yield about 140 m³/ha (2,000 ft³/acre) with another 70 m³/ha  (1,000 ft³/acre) from thinnings (13).

    One 14-year-old plantation had a mean diameter of 27 cm (11 in) and  height of 19 in (61 ft) and yielded 217 m³/ha (3,100 ft³/acre)  (13). Another author in India suggests that silk-oak at 10 to 15 years and  1,000 stems per hectare (370/acre) yields 10 to 12 m³/ha (143 to 172  ft³/acre) (10). In the western Himalayas, 6-yearold silk-oak had  outgrown 45 other species, including such fast growers as Eucalyptus  globulus, Populus x euroamericana, and Albizia lebbek (17).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Molecular Biology and Genetics

Genetics

No studies of the genetics of the species have been reported (2). A test  of 11 different genera in Brazil showed 1-year-old silk-oak seedlings to  be the most uniform in height growth (Silva and Reichmann 1975 cited in  2).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Molecular Biology

Statistics of barcoding coverage: Grevillea robusta

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 16
Species With Barcodes: 1
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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: NNA - Not Applicable

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NatureServe Conservation Status

Rounded Global Status Rank: GNR - Not Yet Ranked

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Relevance to Humans and Ecosystems

Benefits

Uses

"

The timber is of medium strength and is used for furniture, packing cases, flooring, paneling, plywood and the manufacture of small wooden items such as pencils.

"
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Folklore

Planted as a shade tree in coffee and tea plantations.

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Special Uses

Grevillea robusta is a popular ornamental because of its  fernlike foliage even in areas where it does not flower abundantly, such  as California and Florida north of Miami. In more tropical climates its  showy flowers cause it to be widely used.

    It has been planted extensively in India and Sri Lanka as shade for tea,  and in Hawaii, India, and Brazil to some extent as shade for coffee  (2,12,14,16). It is frequently used as a windbreak, although opinions  differ as to its wind firmness and branch-shedding tendencies (2).  Silk-oak is an important honey tree in India where it is also regarded as  a good fuelwood producer (13).

    The tree produces an attractively figured, easily worked wood, which was  once a leading face veneer in world trade, where it was marketed as "lacewood."  The wood contains an allergen that causes dermatitis for many people (15).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Wikipedia

Grevillea robusta

Leaves and flowers

Grevillea robusta, commonly known as the southern silky oak or silky oak, or Australian silver oak, is the largest species in the genus Grevillea of the family Proteaceae. It is not closely related to the true oaks, Quercus. It is a native of eastern coastal Australia, in riverine, subtropical and dry rainforest environments receiving more than 1,000 mm per year of average rainfall.

Description[edit]

It is a fast-growing evergreen tree, between 18–35 m (59–115 ft) tall, with dark green delicately dented bipinnatifid leaves reminiscent of a fern frond. It is the largest plant in the Grevillea genus, reaching diameters in excess of 1 m (3 ft). The leaves are generally 15–30 cm (6–12 in) long with greyish white or rusty undersides.

Its flowers are golden-orange bottlebrush-like blooms, between 8–15 cm (3–6 in) long, in the spring, on a 2–3 cm long stem and are used for honey production. Like others of its genus, the flowers have no petals, instead they have a long calyx that splits into 4 lobes.[1] The seeds mature in late winter to early spring, fruiting on dark brown leathery dehiscent follicles, about 2 cm long, with one or two flat, winged seeds.

Uses[edit]

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.

Recently G. robusta has been used for side and back woods on guitars made by Larrivée and others, because of its tonal and aesthetical qualities.

Cultivation[edit]

When young it can be grown as a houseplant where it can tolerate light shade, but prefers full sun as 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 −8 °C (18 °F).[2] It needs occasional water but is otherwise fairly drought-resistant.

Grevillea robusta is often used as stock for grafting difficult-to-grow grevilleas.

Care needs to be taken when planted near bushland as it can be weedy.

The tree has been planted widely throughout the city of Kunming in south-western China forming shady avenues.

This plant has gained the Royal Horticultural Society's Award of Garden Merit.[3]

G. robusta is also grown in plantations in South Africa[4] and can also be grown alongside maize in agroforestry systems.[5]

Toxicity and allergic reactions[edit]

The flowers and fruit contain toxic hydrogen cyanide.[6] Tridecylresorcinol in G.robusta is responsible for contact dermatitis.[7]

References[edit]

  1. ^ RHS A-Z encyclopedia of garden plants. United Kingdom: Dorling Kindersley. 2008. p. 1136. ISBN 1405332964. 
  2. ^ "Garden Guides: Silkoak". 
  3. ^ "Grevillea robusta AGM". RHS Plant Finder. Royal Horticultural Society. Retrieved 27 July 2013. 
  4. ^ Overseas-grown Australian Timber Species Retrieved on 8 December 2008
  5. ^ Jackson, N. (2000). "Tree pruning as a means of controlling water use in an agroforestry system in Kenya". Forest Ecology and Management 126 (2): 133–152. doi:10.1016/S0378-1127(99)00096-1.  edit
  6. ^ Everist, S.L., Poisonous Plants of Australia, Angus & Robertson, 1974.
  7. ^ 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
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Notes

Comments

Wood is used in furniture and panelling. Fruits and seeds contain Cyanophoric glucosides.
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