C. scoparius is an unarmed leguminous shrub, having several erect or ascendant stems which can later collapse to become prostrate where crushed by snow (Hosking et al.,1998). Plants grow to 4 m high, and often form dense thickets in cooler areas. Branches are green, five-angled and mostly glabrous. Leaves are usually three-foliate, petiolate to subsessile, but one-foliate and sessile on young growth. Leaflets are narrow-elliptic to obovate, 5-20 mm long and 1.5-8 mm wide, with scattered hairs on the upper surface and numerous short hairs on the lower surface. Flowers are pedicellate, solitary or in pairs, and borne in the axils on 1-year-old stems. The calyx is glabrous, ca 6 mm long, two-lipped, upper lip with two teeth, lower lip with three teeth, all teeth usually much shorter than the lips. The corolla is golden yellow, 15-25 mm long. Fully developed pods are 2.5-7 cm long and 8-13 mm wide, oblong, dehiscent, strongly compressed, with brown or white hairs on the margin, otherwise glabrous, initially green then black at maturity. Plants are deciduous in winter in colder areas and in summer in areas with summer drought. The plant is most easily distinguished from other closely related species by its five-sided green stems, its yellow, pea-like flowers, and pea-like pods mainly 2.5-7 cm long with hairy margins (see Pictures). In the field, broom plants are conspicuous because of their dark green colour (compared to e.g. the grey-green colour of the more robust C. striatus) and especially their abundant large flowers at the peak of flowering.
Related invasive species
- Cytisus scoparius
Related Farm Practice
- Shading
- Drought
- Damage
- Plantations
- Forestry
- Natural regeneration
C. scoparius is a perennial shrub that has been widely commercialized as an ornamental in temperate and subtropical regions of the world. It is a prolific seeder that escaped from cultivation and has become an invasive species and a serious weed in temperate areas of the United States, Canada, Hawaii, Chile and Argentina, the eastern halves of both islands of New Zealand, Australia (including Tasmania), India, Iran, Japan and South Africa (Holm et al., 1979;Parsons and Cuthbertson, 1992;Hosking et al., 1998;Peterson and Prasad, 1998;Isaacson, 2000). C. scoparius is an aggressive fast-growing invader with the capability to grow forming dense impenetrable monospecific stands that degrade native grasslands, forests, rangelands, and agricultural lands;prevent the regeneration of natural forests and prairies;and create fire hazards (Syrett et al., 1999;USDA-NRCS, 2016). Because of its association with nitrogen fixing bacteria, it is very competitive in areas with poor soils and can alter the nutrient cycling of invaded areas (Peterson and Prasad, 1998).
C. scoparius is also very common and widespread within its native range and reaches densities where it is considered a weed (Maury, 1963;Engel, 1964). Consequently, in many European countries (within its native range) it has been included in national lists of invasive species (DAISIE, 2016). However, treating this species as invasive in areas within its native distribution range is controversial as it has been present in the European flora for centuries and in many countries where it is now listed as invasive it was previously listed as native (Rosenmeier et al., 2013;DAISIE, 2016).
C. scoparius is a significant weed of forestry, particularly in pine and eucalypt plantations around the world. It either smothers planted saplings or reduces their growth (Peterson and Prasad, 1998;Barnes and Holz, 2000). In some areas, C. scoparius can be beneficial in these situations as a nurse crop protecting samplings from frost damage and other types of exposure (Peterson and Prasad, 1998), but it can also be associated with higher levels of plantation diseases (Peterson and Prasad, 1998). Once the plantation species grow above plants of C. scoparius, the impact on tree growth is minimal. In native woodland situations broom can prevent natural regeneration by shading (Hosking et al., 1998) and allelopathy (Nemoto et al., 1993).