Laburnum

For the locality of Melbourne called Laburnum, see Laburnum, Victoria.

For other uses, see Golden Chain.

"Indian laburnum" is the golden shower tree, a distant relative of the genus Laburnum.

Laburnum
Common laburnum – flowers
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Fabales
Family:	Fabaceae
Subfamily:	Faboideae
Tribe:	Genisteae
Genus:	Laburnum Fabr.
Species
See text.

Laburnum, sometimes called golden chain, is a genus of two species of small trees in the subfamily Faboideae of the pea family Fabaceae. The species are Laburnum anagyroides—common laburnum and Laburnum alpinum—alpine laburnum. They are native to the mountains of southern Europe from France to the Balkans.

Some botanists include a third species, Laburnum caramanicum, but this native of southeast Europe and Anatolia is usually treated in a distinct genus Podocytisus, more closely allied to the Genisteae ("brooms").

Description

The Laburnum trees are deciduous. The leaves are trifoliate, somewhat like a clover; the leaflets are typically 2–3 cm (1–1 in) long in L. anagyroides and 4–5 cm (1.5–2 in) long in L. alpinum.

They have yellow pea-flowers in pendulous leafless racemes 10–40 cm (4–15.5 in) long in spring, which makes them very popular garden trees. In L. anagyroides, the racemes are 10–20 cm (4–8 in) long, with densely packed flowers; in L. alpinum the racemes are 20–30 cm (8–12 in) long, but with the flowers sparsely along the raceme. The fruit develops as a pod and is extremely poisonous, it can be used medicinally.

The yellow flowers are responsible for the old poetic name 'golden chain tree' (also spelled golden chaintree or goldenchain tree).

Laburnum tree in full flower

All parts of the plant are poisonous, although mortality is very rare. Symptoms of laburnum poisoning may include intense sleepiness, vomiting, convulsive movements, coma, slight frothing at the mouth and unequally dilated pupils. In some cases, diarrhea is very severe, and at times the convulsions are markedly tetanic. The main toxin in the plant is cytisine, a nicotinic receptor agonist.

It is used as a food plant by the larvae of some Lepidoptera species, including the buff-tip.

Uses

Woodworking

Laburnum has historically been used for cabinetmaking and inlay, as well as for musical instruments. In addition to such wind instruments as recorders and flutes, it was a popular wood for Great Highland Bagpipes before taste turned to imported dense tropical hardwoods such as Brya ebenus (cocus wood), ebony, and Dalbergia melanoxylon (African blackwood). The heart-wood of a laburnum may be used as a substitute for ebony or rosewood. It is very hard and a dark chocolate brown, with a butter-yellow sapwood.

Cultivation

Laburnum species and hybrids are cultivated as ornamental trees for gardens and parks. They are also trained as espaliers on pergolas, for ceilings of pendant flowers in season.

Most garden specimens are of the hybrid between the two species, Laburnum ×watereri 'Vossii' (Voss's laburnum), which combines the longer racemes of L. alpinum with the denser flowers of L. anagyroides; it also has the benefit of low seed production. It has gained the Royal Horticultural Society's Award of Garden Merit.

Cultural references

In the TV mystery series Mother Love, Helena (Diana Rigg) muses over what plant she should use to poison a pair of children and chooses the laburnum, saying, "Laburnum! Such a pretty tree—and so many of them!" In the Doctor Who serial "The Mark of the Rani", the Sixth Doctor suggests that if The Master turned into a tree, it would be a laburnum, because they have poisonous pods.

The novel A Melon for Ecstasy by John Fortune and John Wells is, in part, about the main character's forbidden love affair with the laburnum in his back yard. Laburnum seeds are the agent of suspected poisoning in the Daphne du Maurier novel My Cousin Rachel. In Wizardborn, the third book in Dave Wolverton's (David Farland) The Runelords series, Averan, the Earth Warden, chooses her staff of power from the wood of the laburnum tree. Laburnum also provides an important clue in the sixth series episode of the Inspector Lewis TV mystery series, "The Soul of Genius."

E. Nesbit's 1905 book The Railway Children refers to laburnum trees in Chapter 3 (p. 59), when describing Dr. W.W. Forest's front gate: "Mother wouldn't at first, but in the evening she felt so much worse that Peter was sent to the house in the village that had three laburnum trees by the gate, and on the gate a brass plate with W.W. Forest, M.d., on it." J. R. R. Tolkien also refers to the tree on page 14, chapter one of The Hobbit when Bilbo reminisces about the qualities of Galdalf's fireworks: "...They used to go up like great lilies and snapdragons and laburnums of fire and hang in the twilight all evening!" (the hobbit, chapter 1, p. 14). Tolkien's contemporary C. S. Lewis also uses laburnums as part of a descriptive device in The Lion, the Witch and the Wardrobe as he describes the melting snows of Narnia when the White Witch's spell breaks and releases the land, as does P. G. Wodehouse in Bingo and the Little Woman, referring to "the gentle sighing of the breeze in the laburnum."

A laburnum tree is mentioned in Thomas Hood's poem "I remember, I remember":

The lilacs where the robin built,

And where my brother set
The laburnum on his birthday,--

The tree is living yet!

Also mentioned in The Picture of Dorian Gray by Oscar Wilde.

Species

Accepted Binomials

Laburnum comprises the following species:

• Laburnum alpinum (Mill.) Bercht. & J. Presl
• Laburnum anagyroides Medik.

Species names with uncertain taxonomic status

The status of the following species is unresolved:

• Laburnum album J.Presl
• Laburnum alpinum (Mill.) Bercht. ex J. Presl
• Laburnum arboreum J.Presl
• Laburnum biflorum G.Nicholson
• Laburnum fragrans Griseb.
• Laburnum grandiflorum (DC.) J.Presl
• Laburnum heuffelii Wierzb. ex Fuss
• Laburnum ianigerum J. Presl
• Laburnum intermedium Dippel
• Laburnum jacquinianum Dalla Torre & Sarnth.
• Laburnum jaquinianum Dieck
• Laburnum laburnum (L.) Voss
• Laburnum laburnum Dörfl.
• Laburnum lanigerum J.Presl
• Laburnum linneanum Dieck
• Laburnum monadelphum Pritz.
• Laburnum nigricans J.Presl
• Laburnum nigricanum Fuss
• Laburnum nubigenum J.Presl
• Laburnum patens J.Presl
• Laburnum pendulum Raf.
• Laburnum praecox Fuss
• Laburnum purpurascens hort. & Vilm.
• Laburnum purpureum (Scop.) Drapiez
• Laburnum ramentaceum (Sieber) K.Koch
• Laburnum rochelii Wierzb. ex Fuss
• Laburnum serotinum Hort. ex Dippel
• Laburnum sessilifolium J.Presl
• Laburnum spinosum J.Presl
• Laburnum tardiflorum auct.
• Laburnum triflorum J.Presl
• Laburnum variabile hort. & Vilm.
• Laburnum waterii Dippel
• Laburnum weldeni Griseb. ex Lavall.
• Laburnum weldenii Griseb. ex Lavallée

Hybrids

The following hybrids have been described:

• Laburnum ×adami Lavallée
• Laburnum ×watereri (Wettst.) Dippel (L. alpinum × L. anagyroides)

External links

• Flora Europaea: Laburnum
• ILDIS Legume Database
• Laburnum tree video — time lapse of a year in the life of a Laburnum tree.
• Grieve, 'A Modern Herbal' (1931)