This is probably the most common buckthorn (Rhamnus sp., Frangula sp.) in Illinois. The flowers and foliage are rather ordinary in appearance, although the drupes of female plants are somewhat attractive during the winter. Common Buckthorn differs from another introduced species, Frangula alnus (Glossy Buckthorn), by its 4-lobed flowers, finely crenate leaf margins, and narrowly grooved seeds; Glossy Buckthorn has 5-lobed flowers, smooth leaf margins, and seeds that lack grooves. This latter species prefers damper habitats than Common Buckthorn. Other buckthorns in Illinois (both native and introduced) have more elongated leaves with 4-6 pairs of lateral veins. In contrast, Common Buckthorn has 2-3 pairs of lateral veins per leaf. Occasionally new species of buckthorn escape from cultivation (Rhamnus davurica, Rhamnus japonica, & Rhamnus utilis are examples), although it remains to be seen how invasive these introduced species will become.