Know Your Natives – Carolina Buckthorn

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.

Photo 1: Lower portion of this tree, positioned at a woodland edge, is compact and leafy as compared to the more sparse upper portion that extends into the overstory. Top of tree indicated by arrow. Photo – July 21.
Photo 2: This understory tree, located among large canopy trees of other species, has an estimated height of 36 feet and a spread of 19 feet. Dead limb on right is 6 feet above the ground. Photo – October 21.

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.

,Photo 3: The root of this 5-foot tree suggests that the roots of larger trees would be similar, that is, with major roots extending laterally as well as descending to depth.
Photo 4: A display to show changes of color and texture as branches and trunks mature. Diameter of trunk at left (same plant as shown in Photo 3) is ⅝ inch. Branch at far right is current year’s growth with leaves removed. Leaf at right is 6 1/4 inches long and 2 1/4 inches wide. Photo – October 17.
Photo 5: This trunk of a 36-foot tree (also shown in Photo 2) is mostly smooth with whitish splotches and slight fissuring. The trunk has a circumference of 15¾ inches at 5 inches above ground.
Photo 6: Terminal and lateral buds are composed of pubescent miniature leaves which are not protected by scales. With leaves removed, the three vascular bundles can be seen in the leaf scar. Photo – October 6.

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.

Photo 7: The simple, elliptic to obovate-elliptic leaves are shiny dark green above and dull pale green beneath. They have equally spaced, perfectly parallel secondary veins that extend toward the leaf margin. Photo -May 28.
Photo 8: Secondary veins extend to near the leaf margin where they align with the margin and interconnect. Margins are minutely irregularly notched. Upper surface shown on left and lower surface on right. Photo – October 17.

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.

Photo 9: Umbels of 10± flowers are axillary to current-year’s leaves. Naked buds for the next year’s growth can already be seen at top of photo. Leaves are alternate or rarely subopposite. Photo – June 3.

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.

Photo 10: Two small umbels are shown on left and a larger umbel on right. Puberulent peduncles and pedicels are straight and stout. Exterior surface of hypanthium and lobes are similarly pubescent. Photo – May 28.
Photo 11: Inconspicuous petals initially shroud the stamens (see open flowers on left and right). Several flowers have progressed to early fruits. Dense minute pubescence of the petioles can be seen. Photo – May 28.
Photo 12: Petals and stamens are positioned between calyx lobes. Three fused carpels of the pistil form a central column topped with three round, sunken stigmas (flower at upper right). Photo – June 28.

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.

Photo 13: Initially green, fruits are axillary on current-year’s growth. Leaves tend to be larger at and near the ends of branches. Photo – July 21.
Photo 14: Fruits transition from green to red in late summer. Shiny leaves have prominent, equally spaced pinnate venation. Photo – August 23.
Photo 15: Fruits transition from red to black at maturity in the fall. Leaves become yellow or sometimes bronze in fall. Photo – September 21.
Photo 16: The black fruits each contain three stones which are pressed together (shown at right) so that each stone has a rounded side and two flattened sides. Squares = ¼ inch. Photo – October 6.

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

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