Carolina Buckthorn (Frangula caroliniana, formerly Rhamnus caroliniana) of the Buckthorn (Rhamnaceae) family is an elegant, thornless (!), deciduous shrub or small tree, with simple shining leaves and red to black berry-like fruits. (The tiny, whitish flowers are easily overlooked.) The genus name originates from the word “frangible” meaning “easily broken.” The specific epithet recognizes that the species was first described from specimens collected in the Carolinas. It occurs primarily from central Texas to central Missouri, east to Virginia and central Florida. In Arkansas, plants are found statewide except for portions of the Mississippi Alluvial Plain. Habitats vary, with soils acid to limy, moist to dry, in sun to part shade, in woodland margins, glades, bottomlands and stream terraces. The species is also known as Indian-Cherry.
Carolina Buckthorn is typically 10 to 15 feet tall, but may reach 30+ feet, especially on partially shaded sites. On sunny sites, plants develop a denser limb structure and often become rather shrubby. Despite the common name, none of the “Buckthorns” segregated from Rhamnus into the genus Frangula are armed with thorns. In addition, Frangula species are characterized by naked winter buds, that is, buds composed of tightly folded miniature leaves that are not protected by scales––a distinctive character useful for winter identification. Young branches have dense, minute, appressed pubescence (extending onto leaf petioles) that is lost by mid-growing-season. Twig color changes from pale green to tan and ultimately to gray as branches mature. Bark is thin and smooth with slightly raised whitish lenticels and leaf scars as well as whitish splotches and short tight fissures.
Alternate elliptic to obovate-elliptic leaves, with a shiny dark green upper surface and a dull pale green lower surface, have a rounded to cuneate base and an apex that may be acuminate, acute or obtuse. A large leaf may be 6½ inches long, including a ⅝-inch petiole, and 2 inches wide, the largest leaves occurring toward the branch tips. Venation is offset-pinnate, with 8-10 pairs of prominently straight and parallel secondary veins that bend forward near the leaf margin. Margins are irregularly and obscurely crenate. Persistent dense minute pubescence of the petiole extends onto the veins of the blade beneath, with longer scattered hairs between the veins. Upper surface of the leaves feels smooth; lower surface feels corrugated, due to expressed lateral veins. Leaves droop in dry spells, but quickly rebound with renewed moisture. Leaves become yellow to bronze in fall.
The inflorescence, from May into June, consists of axillary umbels of tiny (⅛ inch wide and long), pale green to whitish flowers on short, ascending pedicels. A peduncle may support 1-10 flowers. Peduncles, pedicels, and calyxes are densely puberulent.
The inconspicuous, perfect (with male and female structures) flowers have a small, campanulate (bell-shaped) hypanthium, bearing 5 triangular sepals, 5 petals, and 5 stamens. Petals are smaller than sepals, and the stamens are positioned opposite the petals––a very unusual morphology. The compound pistil in center bears an undivided style with sunken stigmas. Flowers in bud form a 5-sided pyramid and, in bloom, spread wide to form a star. When lobes of the perianth open, the petals are wrapped around the stamens. With the petals unfurled, the pale yellowish-green, strongly ribbed anthers are exposed.
Trees in favorable sites can produce a copious quantity of fruits (drupes). The spherical, ⅜-inch drupes change from green in July, to red in August, and black in October. The black mature drupes have a tiny stubby point at their apex (scar of style). The thin-skinned mature drupes contain three relatively large stones (¼ inch x ⅜ inch) that are pressed together in a white, rather pungent flesh. The black skin of fruits may cause the flesh of a crushed fruit to be purplish The dark brown stones, with tan bases, have a rounded side and two flattened sides with a slight rib separating the flat sides. Fruits, supported by stout peduncles and pedicels, tend to be readily visible between leaves.
Carolina Buckthorn may be an excellent choice for a partially sunny garden border or natural area. With its glossy green leaves and its red to black fruits, it is showy over the entire growing season. Leaves tend to be retained during dry periods, and, though becoming limp, quickly respond to wetter conditions. Rate of growth, size and form vary considerably depending on a tree’s number of sun-hours. Plants in full sun tend to be more densely branched and produce a larger quantity of fruits. Carolina Buckthorn is fairly aggressive at self-seeding so that seedlings may need to be controlled. When other choices diminish, fruits are appreciated by many birds and small and large mammals.
Carolina Buckthorn is the only species of the genus Frangula that occurs in Arkansas. A native species of the same family and somewhat similar character is Lance-Leaf Buckthorn (Rhamnus lanceolata) which occurs in the Ozark Mountains in the northern two tiers of counties in Arkansas. Lance-Leaf Buckthorn is a shrub to 9 feet tall, with smaller and usually more lanceolate leaves, smaller glabrous clusters of 4-petaled, separate staminate and pistillate flowers, and buds with scales. Two non-native species of the genus Rhamnus have been reported escaping at a few sites in the Ozark Mountains, namely European Buckthorn (Rhamnus cathartica) and Dahurian Buckthorn (Rhamnus davurica). These non-native trees have mostly opposite and more rounded leaves; short, thorn-tipped twigs and larger branches; and fruits each with either 3-4 stones (European Buckthorn) or 2 stones (Dahurian Buckthorn).
Article and photographs by ANPS member Sid Vogelpohl