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common broom, Scot's broom, Scotch broom, Scottish broom

Habit 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.

Cytisus scoparius

Phenology Flowering Mar–Jun(–Oct).
Habitat Thickets, roadsides.
Elevation 0–1000 m. (0–3300 ft.)
Distribution
from FNA
AK; AL; CA; CT; DC; DE; GA; ID; KY; MA; MD; ME; MI; MT; NC; NH; NJ; NY; OH; OR; PA; SC; TN; VA; WA; WV; BC; NS; PE; s Europe; w Europe; nw Africa; n Atlantic Islands [Introduced in North America; introduced also in s South America (Argentina, Chile), Pacific Islands (New Zealand)]
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[BONAP county map]
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.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 11.
Parent taxa Fabaceae > subfam. Faboideae > Cytisus
Sibling taxa
C. multiflorus, C. proliferus, C. striatus
Synonyms Spartium scoparium, C. scoparius var. andreanus
Name authority (Linnaeus) Link: Enum. Hort. Berol. Alt. 2: 241. (1822)
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