There is also a native buckthorn (Rhamnus alnifolia), so verify identification prior to removal. Shrubby plant that grows to 6 - 24 feet tall with stems up to 10" diameter. Flowers May to September in clusters of tiny, white, trumpet flowers which become spherical, green, berry-like fruit that turn red then black in the fall. Seeds readily spread by birds and wildlife. Tolerates a wide variety of conditions and forms dense thickets, aggressively crowding out native species.