Comments
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Wood is used in furniture and panelling. Fruits and seeds contain Cyanophoric glucosides.
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Description
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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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Distribution
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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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Distribution
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Cultivated in Nepal and elsewhere; native of Australia.
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Elevation Range
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760-1500 m
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Flower/Fruit
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Fl. Per: March-April.
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Derivation of specific name
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robusta: robust
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- Hyde, M.A., Wursten, B.T. and Ballings, P. (2002-2014). Grevillea robusta A. Cunn. ex R. Br. Flora of Zimbabwe website. Accessed 28 August 2014 at http://www.zimbabweflora.co.zw/speciesdata/species.php?species_id=164130
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Description
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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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- Hyde, M.A., Wursten, B.T. and Ballings, P. (2002-2014). Grevillea robusta A. Cunn. ex R. Br. Flora of Zimbabwe website. Accessed 28 August 2014 at http://www.zimbabweflora.co.zw/speciesdata/species.php?species_id=164130
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Worldwide distribution
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Native of Australia
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- Hyde, M.A., Wursten, B.T. and Ballings, P. (2002-2014). Grevillea robusta A. Cunn. ex R. Br. Flora of Zimbabwe website. Accessed 28 August 2014 at http://www.zimbabweflora.co.zw/speciesdata/species.php?species_id=164130
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Associated Forest Cover
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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).
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Climate
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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).
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Damaging Agents
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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.
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Flowering and Fruiting
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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.
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Genetics
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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).
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Growth and Yield
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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).
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Reaction to Competition
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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).
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Rooting Habit
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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).
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Seed Production and Dissemination
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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).
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Seedling Development
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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.
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Soils and Topography
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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.
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Special Uses
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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).
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Vegetative Reproduction
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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.
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Brief Summary
provided by Silvics of North America
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.
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Distribution
provided by Silvics of North America
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).
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Grevillea robusta
provided by wikipedia EN
Grevillea robusta, commonly known as the southern silky oak, silk oak or silky oak, silver oak or Australian silver oak,[1] is a flowering plant in the family Proteaceae. It is a tree, the largest species in its genus but is not closely related to the true oaks, Quercus. 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 5–40 m (20–100 ft) tall. The bark is dark grey and furrowed. Its leaves are fern-like, 10–34 cm (4–10 in) long, 9–15 cm (4–6 in) 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.[2][3][4]
The flowers are arranged in one-sided, "toothbrush"-like groups, sometimes branched, 12–15 cm (5–6 in) long. The carpel (the female part) of each flower has a stalk 21–28 mm (0.8–1 in) 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.[2][3]
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.[5][6] The specific epithet (robusta) is a Latin word meaning "strong like oak" or "robust".[7]
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, including on Norfolk Island and Lord Howe Island. It has become naturalised in many places, including on the Atherton Tableland in Australia and 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, as "invasive" in Hawaii and as an "invader" in South Africa.[1][2][8]
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.[4]
Recently G. robusta has been used for side and back woods on guitars made by Larrivée and others, because of its tonal and aesthetic qualities.
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 −8 °C (18 °F).[9] 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.[10]
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,[11] and can also be grown alongside maize in agroforestry systems.[12]
In the UK, G. robusta has gained the Royal Horticultural Society's Award of Garden Merit.[13][14]
Toxicity and allergic reactions
The flowers and fruit contain toxic hydrogen cyanide.[15] Tridecylresorcinol in G.robusta is responsible for contact dermatitis.[16]
silky oaks planted in a tea plantation
References
-
^ a b "Grevillea robusta". Queensland Government. Retrieved 19 June 2018.
-
^ a b c Makinson, Robert O. "Grevillea robusta". Royal Botanic Garden Sydney. Retrieved 19 June 2018.
-
^ a b RHS A-Z encyclopedia of garden plants. United Kingdom: Dorling Kindersley. 2008. p. 1136. ISBN 978-1405332965.
-
^ a b "Grevillea robusta". National Arboretum Canberra. Retrieved 18 June 2018.
-
^ "Grevillea robusta". APNI. Retrieved 20 June 2018.
-
^ Brown, Robert (1830). Supplementum primum Prodromi florae Novae Hollandiae. London. p. 24. Retrieved 19 June 2018.
-
^ Brown, Roland Wilbur (1956). The Composition of Scientific Words. Washington, D.C.: Smithsonian Institution Press. p. 556.
-
^ F.A. Zich; B.P.M Hyland; T. Whiffen; R.A. Kerrigan (2020). "Grevillea robusta". Australian Tropical Rainforest Plants, Edition 8. Commonwealth Scientific and Industrial Research Organisation (CSIRO). Retrieved 2 March 2021.
-
^ "Silkoak (Robusta)". Garden Guides. Leaf Group. Archived from the original on 2011-07-16. Retrieved 2019-05-02.
-
^ "Grevillea robusta (silky oak)". Invasive Species Compendium. CAB International. Retrieved 2019-05-02.
-
^ Overseas-grown Australian Timber Species Retrieved on 8 December 2008
-
^ 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.
-
^ "Grevillea robusta AGM". RHS Plant Finder. Royal Horticultural Society. Retrieved 15 July 2020.
-
^ "AGM Plants - Ornamental" (PDF). Royal Horticultural Society. July 2017. p. 43. Retrieved 3 March 2018.
-
^ Everist, S.L., Poisonous Plants of Australia, Angus & Robertson, 1974.
-
^ 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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Grevillea robusta: Brief Summary
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Leaves and flowers
Stamen and pistil
Grevillea robusta, commonly known as the southern silky oak, silk oak or silky oak, silver oak or Australian silver oak, is a flowering plant in the family Proteaceae. It is a tree, the largest species in its genus but is not closely related to the true oaks, Quercus. It is a native of eastern coastal Australia, growing in riverine, subtropical and dry rainforest environments.
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_species_growing_inside_the_Kangla_fort_in_Imphal,_Kangleipak_(Manipur).jpg)
_JCB.jpg)
Leaves and flowers 
Stamen and pistil 
