Trees or shrubs, unarmed. Stems erect, young growth appressed-pubescent, glabrescent, or glabrous. Leaves alternate, palmate; stipules present, minute; petiolate; leaflets 3, subsessile, stipels absent, blade margins entire, surfaces glabrous or pubescent abaxially, glabrous adaxially. Inflorescences 20–50-flowered, axillary, racemes, pendulous [erect]; bracts present; bracteoles near midpoint of pedicel, subopposite. Flowers papilionaceous; calyx zygomorphic, campanulate, bilabiate, lobes 5; corolla yellow, glabrous, banner ovate or orbiculate, keel shorter than wings; stamens 10, monadelphous; anthers dimorphic, shorter ones versatile, alternate, longer ones basifixed, dehiscing apically; ovary stipitate; style glabrous; stigma terminal. Fruits legumes, stipitate, pendulous, subterete, weakly torulose, narrowly ellipsoid to oblong [oblong-linear], indehiscent, constricted between seeds, fleshy, pubescent. Seeds [1]2–4(–8), reniform-compressed; hilum lateral. x = 10.

Distribution

Introduced; s Europe, w Asia, n Africa, introduced also nearly worldwide in temperate areas.

Discussion

Species ca. 3 (2, including 1 hybrid, in the flora).

Laburnum includes three Old World species and one hybrid. Laburnum alpinum (Miller) Berchtold & J. Presl, a native of southern Europe (leaves and fruits glabrous), is cultivated in North America and is not reported to escape; it forms a hybrid with L. anagyroides called L. × watereri. The remaining species sometimes placed in Laburnum, L. caramanicum (Boissier & Heldrich) Bentham & Hooker f., is a shrub native to Greece and southwest Asia that has been infrequently cultivated in the southern United States. It is readily distinguished from other Laburnum by having upright versus pendulous racemes and usually is treated in a disti

In Laburnum, all parts of the plants are toxic and can be lethal if consumed in excess (D. Frohne and H. J. Pfander 2004). The main toxins are a series of quinolizidine alkaloids of the cytisine type.

Selected References

None.

Lower Taxa

Laburnum anagyroides, Laburnum ×watereri

Key

1	Leaflet blades appressed silky-pubescent abaxially; young growth appressed-pubescent; pedicels (4–)8–15 mm; legumes densely appressed-pubescent.	Laburnum anagyroides
1	Leaflet blades glabrous or glabrescent abaxially; young growth glabrescent or glabrous; pedicels 4–9 mm; legumes sparsely appressed-pubescent.	Laburnum × watereri