Rhamnus cathartica
Sp. Pl. 1: 193. 1753. (as catharticus)
Shrubs or trees, (1–)2–8 m, armed with thorns. Branchlets dark to reddish gray or purple, glabrous. Leaves deciduous (often present well after frost), usually opposite to subopposite, rarely alternate, sometimes fascicled on short shoots; petiole 10–27 mm; blade dull green abaxially, glossy darker green adaxially, usually ovate to elliptic-ovate, sometimes broadly elliptic or nearly orbiculate, (2–)4–7 cm, usually 1–2 times longer than wide, herbaceous, base rounded to rounded-truncate or slightly subcordate, margins crenate-serrate, apex acute to rounded, often abruptly short-acuminate, both surfaces glabrous; secondary veins 2–4 pairs, all diverging at nearly same angle or proximal diverging more obtusely. Inflorescences fascicles or flowers solitary. Pedicels 2–4 mm. Sepals 4. Petals 4. Drupes black, globose to depressed-globose, 5–6(–8) mm; stones 3–4. 2n = 24.
Phenology: Flowering Apr–Jun.
Habitat: Vacant lots, fields, forest edges, fencerows, roadsides, stream channels, riverbanks, ravines, floodplains, swampy habitats, deciduous forests.
Elevation: 10–1000(–2000) m.
Distribution
Introduced; Alta., Man., N.B., N.S., Ont., P.E.I., Que., Sask., Ariz., Colo., Conn., Del., Idaho, Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., N.H., N.J., N.Y., N.C., N.Dak., Ohio., Pa., R.I., S.Dak., Utah, Vt., Va., Wash., W.Va., Wis., Wyo., Europe, c, sw Asia (China, Russia in w Siberia), nw Africa.
Discussion
Rhamnus cathartica was introduced to North America as an ornamental shrub in the middle 1800s and was originally used for hedges, farm shelterbelts, and wildlife habitat; it is an aggressive invader of woods and prairies and is able to completely displace native vegetation. W. H. Brewer collected R. cathartica (UC 18526) in the 1800s from an unknown location in California. No specimens have been collected in the state since that time and it apparently is not naturalized there.
Rhamnus cathartica is a primary host for the soybean aphid, Aphis glycines, native to eastern Asia. It uses the buckthorn as a winter host and spreads to soybean in the spring. The insect was first discovered in North America in 2000 in Wisconsin and subsequently has spread to at least 20 states in the United States and three provinces in Canada. The orange-colored wood of R. cathartica is sometimes used by woodcarvers.