F. alnus is a deciduous shrub or small tree usually 4-5 m in height (Tutin et al., 1968), but may grow to 7 m (Gleason, 1963). It develops an erect, slender habit with branches somewhat irregular in alternate pairs, ascending at an acute angle to the main stem (Godwin, 1943). Young twigs are green but turn grey-brown with age and develop red-brown to dark violet tips. Lenticels may be evident as white dots and stripes. Lemon-yellow inner-bark tissues are exposed when the outer-bark is damaged and the young wood is dark brown. Old bark is smooth, except in very old specimens, and readily peels off dead wood. Spines are absent from F. alnus. Leaves are petiolate, obovate in shape, 2-7 cm in length and usually little more than half as wide. They are cuspidate to acuminate in shape, typically ending with a short pointed tip. Leaf margins are entire but wavy, although in seedlings leaves may be serrated. The lower surface of young leaves is pubescent, being covered with dense brownish hairs which are later shed so that older leaves are glabrous and shiny green in colour. Sun leaves are relatively broader and more shiny than shade leaves. The leaves turn yellow, then red in the autumn. Lateral veins are conspicuous on the upper surface of the leaves with 6-12 (commonly 7) pairs running more or less parallel to each other.
F. alnus develops sessile umbels in the leaf axils on young wood with 2-8 flowers borne on stout, unequal, glabrous pedicels 3-10 mm long;occasionally single flowers develop. Individual flowers are greenish-white, about 3 mm in diameter and bisexual. The flowers are 5-merous with broadly obovate petals 1-1.4 mm long and cleft at the tip (Gleason, 1963). Fruits are 6-10 mm in diameter, and change from green to red, then to violet-black on ripening;flowering and fruit development are rather asynchronous, hence all stages of ripening may be present. Each drupe usually contains 2, but occasionally 3, pyrenes or stones which are broadly obovoid in shape, about 5 mm long and 2 mm thick;they have a faint ridge running down the inner face and a deep furrow at the base. Young and Young (1992) report 52 seeds/g for F. alnus. Germination is hypogeal (Godwin, 1943).
Related invasive species
- Frangula alnus
Related Farm Practice
- Wood
- Invasive alien species
- Development
- Hosts
- Communities
- Invasion
- Pests
- Invasive species
- Change
- Cuttings
- Dead wood
F. alnus was introduced to North America from Europe more than 100 years ago. Once established it maintains itself due to prolific seed production, vigorous growth over an extended growing season and its ability to regenerate following burning and cutting. These characteristics make it difficult to eradicate. Repeated cutting and application of herbicides required to eliminate F. alnus is laborious and expensive. Consequently, most restoration work has been conducted in natural ecosystems of special interest. Its adverse effect on native species arises because F. alnus shades out understorey plants. Its aggressive character, especially in wetlands, is widely noted (Catling and Porebski, 1994).
F. alnus is a problem species in native communities because it establishes in dense stands which shade out other understorey species. Possessky et al. (2000) reported a reduction in composition and abundance of the herbaceous cover in riparian habitats in the northern Allegheny Plateau (of Pennsylvania, New York and Ohio, USA) following invasion by F. alnus. Similarly, Reinartz (1997) described how an undisturbed bog community in Wisconsin was invaded by F. alnus in 1955 with a dense tall shrub canopy dominating the site within 12 years. The species is listed as an invasive weed in Tennessee and Wisconsin, USA (Southeast Exotic Pest Plant Council, 1996;Hoffman and Kearns, 1997). F. alnus was recently rated as one of the six principal invasive aliens of wetlands in Canada, and one of four principal invasive aliens in Canadian uplands. In a national survey it was rated second to purple loosestrife (Lythrum salicaria) with respect to the extent to which it is spreading in natural habitats and its severity of impact in Canada (White et al., 1993).
F. alnus is associated with crown rust (Puccinia coronata) which infects several cool season turfgrasses, native grasses and cereals. The uredia, telia and basidiospores are produced on the graminoid hosts, the aecia and pycnia are produced on F. alnus (and Rhamnus cathartica;Partridge, 1998). Alfalfa mosaic virus, which infects a wide variety of plants, including crops, and is vectored by aphids, has also been isolated from young leaves and root cuttings of F. alnus in Italy (Marani and Giunchedi, 2002).