A deciduous shrub up to 5 or 6 ft high in the open; twice as high when drawn up in shrubberies. Although the leaves fall in autumn, the plant, by the greenness of its branches, retains an evergreen aspect through the winter. Branchlets erect, straight, prominently angled, hairy when young. Leaves at the base of the shoot trifoliolate and stalked, those near the end stalkless and often reduced to one leaflet. Leaflets obovate, sometimes narrowly so, 1⁄4 to 5⁄8 in. long, glabrous except beneath when quite young. Flowers a rich glowing yellow, 1 in. long, produced singly or in pairs from the joints of the year-old shoots in May; standard petal round, 3⁄4 in. across; calyx glabrous. Pod 11⁄2 to 2 in. long, hairy, especially on the margins.
Native of W. Europe, and the only cytisus native of the British Isles, over which it is widely spread. C. scoparius has been regarded as a distinct genus, Sarothamnus Wimmer, distinguished by a number of floral characters, of which the chief was the long, incurved, circinnate-convolute style. However, Bentham, in Bentham and Hooker f., Genera Plantarum, Vol. 1, p. 484 (1865), and in his British Flora, ed. 2, p. 110 (1866), reduced it to Cytisus, noting that there are species which ‘show a gradual passage from the long spiral to the short and straight style’. In the Genera Plantarum Sarothamnus was treated as a section of Cytisus, and this was followed by Briquet in his Études sur les Cytises des Alpes Maritimes (1894), where he has eleven species in the section.
cv. ‘Andreanus’. – Similar to the type in habit, foliage, and shape of flower, but with the wing petals of a rich brownish crimson, and the standard petal, though mainly yellow, stained and lined with the same colour. This beautiful and striking variety was discovered by Puissant growing wild in Normandy, about 1884. It succeeds best grafted on laburnum. It comes only partly true from seed, many of its progeny having flowers very poorly coloured as compared with the parent; but some distinct and improved forms have been obtained. One of the first to be put into commerce was ‘Firefly’, raised at the Daisy Hill nursery, Co. Down, around 1906. Directly, or through C. × dallimorei (q.v.), ‘Andreanus’ has played an important part in the formation of the garden brooms. Plants similar to it have been found elsewhere, for which the group-name is f. andreanus (Puissant) Zab.
cv. ‘Pendulus’. – This variety is not only distinct because of its low prostrate habit (pendulous only when grafted on standards of laburnum), it is particularly showy because of the large size of its flowers. It appears to be a form of var. prostratus (see below).
var. prostratus (C. Bailey) A. B. Jacks. Sarothamnus scoparius subsp. maritimus (Rouy & Fouc.) Ulrich – Stems prostrate; leaves and young twigs densely silky-hairy. According to Flora of the British Isles (1962), where it is treated as a subspecies, it is found on cliffs in W. Cornwall and the Channel Islands, and breeds true. Similar plants are found on the continent on the North Sea coast and in the southern Alps.
f. sulphureus (Goldring) Rehd. f. ochroleucus Zab. – Flowers sulphur-yellow; found occasionally in the wild state. The garden clone ‘Moonlight’ belongs here; it is also characterised by its dwarfer, flatter and more compact habit.
Whilst the ordinary broom, in spite of its great beauty, may be considered too common a shrub to deserve a place in the garden proper, it is admirable for semi-wild spots, dry banks, and such-like places. It is best increased by seed. For the propagation of the garden varieties see the introductory paragraphs on the genus.