Laburnum Medik. (1787), in the family Leguminosae subfamily Papilionoideae, contains 2 species in Europe. Description Trees to 10m, or shrubs. The leaves are alternate, deciduous, pinnate, with 3 leaflets. The flowers are pea-like, in elongated hanging bunches, yellow. Sepals 5, unequal, joined at the base to form a toothed calyx. Petals 5, unequal, the uppermost a broad standard enfolding the 2 outer wings, the 2 lowest forming a keel that encloses the stamens, style, and ovary. Stamens 10, all the filaments joined into a tube. Ovary superior, with 1 carpel containing several ovules; style 1. Pollination is by bees. The pods are flattened, slightly narrowed between the seeds. Key Recognition Features The 3 leaflets and hanging bunches of yellow flowers. Evolution and Relationships Petteria ramentacea (Sieb.) C. Presl., from the mountains of the Balkans, is rather similar, but has short, upright spikes of flowers, as does Podocytisus caramanicus Boiss. & Heldr., which was sometimes included in Laburnum, but which has a winged pod. Ecology and Geography From France to eastern Europe. Laburnum alpinum (Mill.) Bercht. & C. Presl on moist, gravelly slopes, L. anagyroides Medic. in subalpine woods on limestone. Comment Laburnums are commonly grown ornamental trees; the seeds and wood contain the very poisonous alkaloid cytisine. The longest bunches of flowers are produced by L. x watereri ‘Vossii’, a hybrid between the 2 wild species, which is mainly sterile. Laburnum wood is yellowish in colour and durable, and was popular as a veneer in English furniture in the late 17th century. |
