Cytisus scoparius
Enum. Hort. Berol. Alt. 2: 241. 1822.
Shrubs (0.7–)1.5–3 m; twigs erect or ascending, green, strongly 5-angled, pubescent or glabrescent. Leaves 12–15 mm; petiole (2–)6–10 mm, densely pilose, appressed-villous, or glabrate; leaflets (1 or)3 or 5 (often unifoliolate in new growth), blades obovate or oblong, 5–6.5(–9) × (1.5–)2–4 mm, base rounded, apex abruptly acuminate or cuspidate, surfaces lustrous with age, puberulent or glabrous. Inflorescences erect, 1(2 or 3)-flowered. Pedicels (3–)6–10(–12) mm, glabrous. Flowers: calyx campanulate, 5–7 mm, lips barely lobed, puberulent or glabrous; corolla usually yellow, rarely white throughout, wings sometimes reddish, 16–20(–25) mm, banner reflexed or not. Legumes laterally compressed, narrowly oblong, 3.1–4(–5.5) cm, surfaces glabrous, margins villous. Seeds 4–12, brown, reniform, 2–3 mm. 2n = 24, 46, 48.
Phenology: Flowering Mar–Jun(–Oct).
Habitat: Thickets, roadsides.
Elevation: 0–1000 m.
Distribution
Introduced; B.C., N.S., P.E.I., Ala., Alaska, Calif., Conn., Del., D.C., Ga., Idaho, Ky., Maine, Md., Mass., Mich., Mont., N.H., N.J., N.Y., N.C., Ohio, Oreg., Pa., S.C., Tenn., Va., Wash., W.Va., s, w Europe, nw Africa, n Atlantic Islands, introduced also in s South America (Argentina, Chile), Pacific Islands (New Zealand).
Discussion
Cytisus scoparius is a problem exotic (C. C. Bossard 1991, 1993, 1996), especially in the coastal regions of Oregon, Washington, and southern British Columbia, where infestations cover nearly one million hectares. It has long been in cultivation and was introduced to North America in 1850. Plants with reddish wing petals have been distinguished as var. andreanus. Forms with white petals, double-petaled flowers, and dwarf, compact, or procumbent growth forms are known.
Cytisus × dallimorei Rolfe, the hybrid of C. scoparius and C. multiflorus, has been recorded from California.
Selected References
None.