U. europaeus is a woody, spiny shrub that normally grows to 2-2.5 m tall in its native range (Clapham et al., 1987), but up to 7 m tall where introduced such as in New Zealand (Lee et al., 1986). It normally grows erect with ascending stems. It is densely branched in the younger outer layers, but eventually bare at the base. It can adopt a prostrate habit where grazing is heavy, or where exposed to severe wind (Clements et al., 2001). It has shallow lateral roots that are often heavily nodulated, and often has a long central taproot (Grubb et al., 1968;Richardson and Hill, 1998). Seedlings have juvenile leaves that are usually trifoliate, and these are often retained basally in the first year of growth in a form resembling a rosette. As the primary stem begins to grow, spines (modified primary branches) begin to form in the axils of reduced leaves. Secondary and tertiary spines usually form on the primary spine (Millener, 1961;Richardson and Hill, 1998). The deeply-ridged green stems are clothed with sparse hairs, and spines are alternate. Green stems have a pronounced wax layer (Zabkiewicz and Gaskin, 1978a) and normally end in a terminal spine. Leaves are reduced to insignificant scales or phyllodes at the junction of the spine and the stem. The yellow, pea-like flowers are borne singly or in small axillary clusters. The flowers are 1.5-2 cm long. Petals are enclosed by two bracteoles 2-4 mm long, and by the calyx, which is two-thirds the length of the corolla. The calyx is covered with spreading hairs. The pods are initially green and pubescent but turn black as they mature. Seeds are dark brown, dark green or black, sub-ovate (unevenly sub-spherical) and 2-4 mm long, each bearing a yellow elaiosome (aril). There are one to six seeds per pod. U. europaeus subsp. europaeus has bracteoles that are ovate, sub-acute and 2-4 mm wide, and this subspecies occurs throughout the range of the species. U. europaeus subsp. latebracteatus is native only in north-western Spain and central Portugal, mainly near the coast, and has bracteoles that are sub-orbicular, obtuse and 2-4 mm wide (Heywood and Ball, 1968).
With the advent of modern fencing methods, it is unlikely that U. europaeus will ever be introduced to another country for this purpose, and it is also unlikely that U. europaeus would be imported in seeds for sowing because the seed is large and an obvious contaminant. However, it could be transported inadvertently in mud on vehicles, on imported animals or in imported livestock feed. It is a declared noxious weed in four states of the USA;California, Hawaii, Oregon, Washington (USDA-ARS, 2007).
Related invasive species
- Ulex europaeus
Related Farm Practice
- Grazing
Related location
- Portugal
- Spain
- New Zealand
U. europaeus was spread intentionally through most of the world in the 1800s and 1900s as a hedge plant, an ornamental and as a forage, although it is unlikely that it will be distributed to new areas for these purposes in future. It has large seeds and there is a threat from inadvertent introduction, but this is not high. U. europaeus was already declared a noxious weed 100 years ago in Australia and New Zealand, and is now a serious weed in many other countries, and poses a threat elsewhere where it is present but not yet invasive. It is an aggressive colonizer of disturbed habitats, and the risk from continued invasion in suitable climatic zones in countries where present is high. It is a tough, spiny, long-lived, tall shrub with a long-lived seed bank and is difficult to control. Thickets displace vegetation in grassland habitats, and outgrow and supplant tree seedlings in plantation forests. Heavy infestations modify soil and hydrological conditions, and so modify ecosystem processes. This plant poses a serious fire risk for indigenous ecosystems as well as managed habitats and human habitations.
Although often used as a hedging plant, U. europaeus is not generally a weed of crops, but does invade pasture land, and has become a serious environmental weed in some countries.