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FALSE ACACIA

BLACK LOCUST

Robinia pseudoacacia

Pea Family [Fabaceae]

month8may month8jun month8june

category
category8Trees
 
category
category8Deciduous
 
category
category8Broadleaf
 
status
statusZneophyte
 
flower
flower8white
 
morph
morph8zygo
 
petals
petalsZ5
 
stem
stem8round
 
stem
stem8spines
thorns
smell
smell8scent smell8scented smell8fragrant
scent
toxicity
toxicityZmedium
 
contact
contactZlowish
 

15th July 2005, Silverdale, Cumbria. Photo: © RWD
Several cultivars exist, this one (and the most popular in gardens) being Golden Robinia 'Frisia' with yellow leaves maturing lime-green. Many other variants exist as well as a golden-leaved version 'Aurea' but which is now very rare gardens. The wild tree grows up to 29m.


6th Oct 2013, Castlefields canal basin, M/cr. Photo: © RWD
Leaves pinnate and a fresh bluish-green colour.


6th Oct 2013, Castlefields canal basin, M/cr. Photo: © RWD
Leaflets elliptical, many slightly broader at stalk end.


6th Oct 2013, Castlefields canal basin, M/cr. Photo: © RWD
The 10-25cm long pinnate leaves are alternate on dark-red ribbed shoots, the stronger ones possessing sharp spines. Leaves have between 9 and 23 un-toothed oval leaflets, each 4 x 2cm.


26th May 2014, Castlefields canal basin, M/cr. Photo: © RWD
At the start of summer after hot years a laburnum-like cascade of flowers cascades downwards. These shown are only short cascades, and most are as yet un-opened.


26th May 2014, Castlefields canal basin, M/cr. Photo: © RWD
Un-opened flower buds. The sepals are reddish, the buds creamy, opening white.


26th May 2014, Castlefields canal basin, M/cr. Photo: © RWD
When open the flowers are white and droop downwards in a spike. New leaves are paler and soon lose their short hairs.


26th May 2014, Castlefields canal basin, M/cr. Photo: © RWD
The flowers have a large banner petal at the rear.


26th May 2014, Castlefields canal basin, M/cr. Photo: © RWD
Flowers may have a hint of creaminess or greeniness about them.


26th May 2014, Castlefields canal basin, M/cr. Photo: © RWD
A banner at the top, two wings pointing forwards and two keels mostly within the wings.


26th May 2014, Castlefields canal basin, M/cr. Photo: © RWD
Banner at top, wings either side and the keel has a greenish pointed tip.


26th May 2014, Castlefields canal basin, M/cr. Photo: © RWD
Keel on the right in this photo


26th May 2014, Castlefields canal basin, M/cr. Photo: © RWD
The stamens with anthers and style are usually well hidden within the keel but here just discernible in the centre.


6th Oct 2013, Castlefields canal basin, M/cr. Photo: © RWD
Obverse of leaf.


26th May 2014, Castlefields canal basin, M/cr. Photo: © RWD
Leaf by transmitted light sowing veins and short stalk.


26th May 2014, Castlefields canal basin, M/cr. Photo: © RWD
The pods only just starting to grow. They will eventually be up to 8cm long.


15th Oct 2013, Walkden, Gtr M/cr. Photo: © RWD
The sharp spines on stronger dark-reddish shoots are usually in pairs beside each tiny scale-less bud (but which are hidden in summer by the base of the leaf-stalk). Leaflets have a minute but soft bristle at the tip.


1st June 2014, Bury, Lancs. Photo: © RWD
The bark is pale grey and smooth at first but quickly develops deep mostly vertical long fissures and becomes very craggy.


Not to be semantically confused with : Honey Locust (Sophora japonica) [a tree of similar name belonging to a differing Genus within the Pea Family (Fabaceae)]

Some similarities to : Laburnum (Laburnum anagyroides) but that has yellow flowers in drooping spikes (racemes).

Uniquely identifiable characteristics

Distinguishing Feature :

No relation to : False Cypress [a coniferous tree with similar name] or False Rowan, False , False Sedge, False Oxlip, False Fennel, False Grass-poly, False Fox Sedge, False Brome, False Oat-grass, .

The flowering spikes droop in up to 65mm long racemes, shorter than most Laburnums. Only after a hot previous year does the plant produce flowers in early summer, 2013 had a long hot and warm spell so the above tree flowered in 2014. The bark is pale grey and smooth at first but quickly develops deep mostly vertical long fissures and becomes very craggy. The shoots are dark red, ribbed, with the stronger ones having pairs of sharp spines not easily visible to catch the unwary. Like most, if not all plants of the Fabaceae family, it is capable of fixing its own nitrogen.

It propagates by suckering, only seldom by seed. It sometimes forms thickets and is found in woods, and heaths. It is non-native, introduced into the UK in 1636. Originally native to the SE of USA, it is now found naturalised in the UK, temperate parts of North America, Europe, Asia and South Africa, being regarded as invasive in some regions, such as the UK.

It is poisonous containing Robin, a phytotoxin and a toxalbumen which inhibits protein synthesis, also Robitin the glycoside of Robin. Heating Robin destroys its toxicity. The poisons are mostly present in the seeds, young leaves and the inner bark. Robitin is present in the bark at 1% and is a recognised poisoner of cattle, rabbit, and horse the toxic dose in horses being just 1.5mg, 20mg for cattle and 500mg in rabbits. Black Locust also contains another phytotoxin, phasin.

Ingestion can cause anorexia and bloody diarrhoea, cold arms and legs, dilation of pupils, paleness, shock, colic, depression, weakness, tachycardia and irregular heartbeat but it is rarely fatal although the laminitis can be a severe after-effect.

Some of the toxins within the Black Locust are harvested to make pharmaceuticals as an analgesic and to treat ulcers and intestinal problems.

The flowers can apparently be battered, deep fried then eaten and are toxic only if consumed in large quantities. They are very fragrant and yield an aromatic essential oil that is used to make perfumes. The essential oil is dominated by two ingredients, 2-AminoBenzaldehyde which is present mostly in the flowers and is responsible for their perfumery and 3(Z)-Hexen-1-ol (aka 'Leaf Alcohol' present mostly in the leaves.

FLAVONOLS

Additional constituents are Acetin and Robinetin (aka Robinethin) (a flavonoid and colourant contained in the bark which, with alum, can be used as a brownish-orange dye), but their toxicity is not known.

The bark is highly combustible but is apt to release sparks. The Robinetin (and the other flavonols DiRobinetin and Taxifolin [aka 'Toxifolin'?]) within the bark, which comprise up to 6% of the dry weight, render the wood highly resistant to rotting. Compared with Quercetin, another flavonol (but one not found in False Acacia), Taxifolin has low toxicity. The wood is highly prized for its water and weather resistance and its durability, and for this reason is used to build ships hulls, the decking on ships and masts as well as for outdoor posts and roofing. The effectiveness of these inherent flavonols in preserving the wood has been shown to be just as efficacious as impregnation with PentaChloroPhenol or Chromated Copper Arsenate and much more environmentally friendly, containing neither organochlorides, chromium, copper or arsenic.


The tree also contains the non-toxic Robinin (aka Robinine) (a flavonol glycoside being the triple rhamnoside glycoside of Kaempferol). The kaempferol flavonol moiety is shown in black, the glycoside moieties in red.


  Robinia pseudoacacia  ⇐ Global Aspect ⇒ Fabaceae  

Distribution
 family8Pea family8Fabaceae

 BSBI maps
genus8Robinia
Robinia
(False-Acacia)

FALSE ACACIA

BLACK LOCUST

Robinia pseudoacacia

Pea Family [Fabaceae]