Lamurnum Arch, Whidbey Island, WA

Laburnum, commonly 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 Balkan Peninsula.
Some botanists include a third species, Laburnum caramanicum, but this native of southeast Europe and Asia Minor is usually treated in a distinct genus Podocytisus, more closely allied to the brooms.

The Laburnum trees are deciduous. The leaves are trifoliate, somewhat like a clover; the leaflets are typically 2–3 cm (0.8–1.2 in) long in L. anagyroides and 4–5 cm (1.6–2.0 in) long in L. alpinum.
They have yellow pea-flowers in pendulous racemes 10–30 cm (4–12 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 yellow flowers are responsible for the old poetic name 'golden chain tree' (also spelled golden chaintree or goldenchain tree).
All parts of the plant are poisonous, and can be lethal if consumed in excess. 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.