Identifying characteristics:
The common buckthorn is a large shrub or low-branched tree to 26 feet, with
stout, crooked branches and rigid, spine-tipped twigs. The 1.5- to 3-inch-long
leaves are deciduous, simple, subopposite
and toothed along their margins with gland-tipped teeth. The upper surface
is smooth and dark green, with 3 to 5 pairs of strongly curved veins. Leaves
remain attractive throughout the season, and remain green long after other
species have lost their leaves. Fall foliage is green or yellowish-green.
The small, yellowish-green flowers
are bisexual or unisexual, appearing in few-flowered clusters from the leaf
axils in May and June. Flower parts are in groups of 4. The fruits are rounded, black, juicy berries. Solitary
or in dense clusters, they ripen in August and September, persisting on
the twig into winter. As the name "cathartica" suggests,
the fruits are a strong laxative. The immature fruits are a source of green
dye called "Chinese Green." The buds are ovoid and appressed
to the twig, with about 6 dark brown bud scales. The bark
is grayish-brown and the loose ends of the smooth bark form tight curls.
The lenticels are horizontally elongated.
Similar species:
Ecology:
Distribution: The common buckthorn is native to Europe and western
and northern Asia. It was introduced for hedge plantings, later escaping
and becoming naturalized across much of Iowa, where it is considered a primary
noxious weed. There are three native buckthorns in eastern North America:
the Carolina buckthorn (R. caroliniana), the lance-leafed buckthorn
(R. lanceolata), and the alder-leafed buckthorn (R. alnifolia).
The European buckthorn (R. frangula) and the common buckthorn (R.
cathartica) are, however, becoming the most common species.
Habitat: In the British Isles, the common buckthorn is a common hedge or woodland shrub found on chalk soils. It will adjust to any soil, even growing on very wet sites, and will tolerate full sun or semi-shade. It is hardy in the US from zone 2 to 7, and has naturalized in Iowa, now often found in vacant lots, along fencerows, and in open woods. This species is the alternate host of Puccinia coronata, an organism causing oat leaf rust. It is susceptible to leaf spot, rust, powdery mildew, aphids and 3 types of scale-black, gloomy and ivy scale.
Uses:
Wood: The bark of a western species, the cascara buckthorn (R.
purshiana), is an important source of laxative chemicals.
Wildlife: Although the black fruits are a strong laxative and cause nausea in humans, they are eaten by birds. Bees and flies feed on the flower nectar.
Horticulture: The common buckthorn transplants easily, is adapted to harsh urban conditions, and responds well to pruning. This species is used as a hedge plant, for screening and as a background plant in difficult conditions. Although it is a tough, adaptable tree useful for planting in areas where few others will survive, this tree must be planted only after careful consideration, as it spreads rapidly by seed to areas where it is often not wanted.
