Glossy Buckthorn is an erect perennial shrub introduced from Europe that has naturalized and is invasive. While usually found as a multi-stemmed shrub, older specimens can develop into a single trunk tree that will reach 20 feet in height.
The bark is a smooth grayish-brown with some raised whitish lenticels that will become shallow fissures on larger older stems. Sapwood is yellow and heartwood is orange.
Twigs are slender, gray-brown to reddish-brown with some fine gray hair and lacking thorns. Buds are tan.
Leaves are alternate, simple, elliptical to oblong in shape, 2 to 4 inches long. Margins are smooth, sometimes wavy, the upper surface a shiny dark green, pale underside, and with a short stalk with fine hair. Leaf veins have one central vein with 5 to 10 pair of parallel lateral veins, which curve toward the tip at the leaf margins. Leaves are a little broader near the apex which has a slight point.
The Inflorescence is a small group (a fascicle) of 1 to 8 flowers rising from the leaf axils in late spring after the leaves have opened. The fascicle is not stalked but the flowers have short stalks - to 10 mm. The fascicles will appear at multiple leaf nodes along the twig.
Flowers: Individual flowers are very small, bell shaped with 5 small pale yellow-green petals and 5 larger yellow-green sepals, both with pointed lobes. The calyx is hemispheric in shape on a long stalk. While the flowers are perfect they require insect pollination. There are five stamens placed with the petals and a single style leading to a multi-celled ovary.
Fruit: Flowers mature to a 1/4 inch juicy drupe that turns from green to reddish and then to black, each containing 1 to 2 (usually 2) yellowish-brown seeds (nutlets), 5 to 6 mm long, that are ovoid in shape but flattened and dimpled, with a ridge line on one of the flattened sides, and with a beak at one end. It is not uncommon to find fruit in all three stages of coloration on the same branch and sometimes even with flowers still present.
Habitat: Glossy Buckthorn grows in many moist environments from swamps to meadows to wood edges. It is shade tolerant. It forms thickets and the seeds can be widely dispersed by birds as the drupe produces a laxative effect on birds, but only larger birds can probably handle the larger nutlets. Cut stems must be treated with a brush or stump killer to prevent regeneration.
Names: This plant was formerly classified by Linnaeus in the genus Rhamnus as Rhamnus frangula in 1753 but is now in the genus Frangula. This was primarily due to Rhamnus having flowers with both 4-parted and 5-parted corollas but separate sexes, while Frangula has flowers with 5-parted corollas and perfect flowers, with no thorns on the stems. The name Frangula, means brittle wood while the species, alnus, refers to this plants tendency to grow together with some of the alders. The author name for the plant classification, from 1768, "Mill." refers to Philip Miller, Scottish botanist (1691-1771) who was chief gardener at the Chelsea Physic Garden and wrote "The Gardener's Dictionary".
Comparisons: Glossy Buckthorn can be confused with the native Alder-leaf Buckthorn, Rhamnus alnifolia, which also has flowers and fruit strung our along the twig but there the leaves have serrated edges, only 5 to 7 pairs of lateral veins and while the flowers are also 5-parted, they are unisexual. Another species is Common Buckthorn, Rhamnus cathartica, whose leaves are also serrate, but not shiny, and the black drupes develop all at one time and do not go through a red stage, the flower (4-parted) clusters are much more dense and the twigs also have thorns. All three retain their green leaves late into autumn when most deciduous species have shed theirs.
Above: Glossy buckthorn usually appears as a multi-stemmed shrub, but can grow into a small tree. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.
Above: 1st photo - The flower has 5 sepals much larger than the 5 petals. Stamens and their dark anthers rest against the small petals. In the center is the greenish style with divided blunt tips. 2nd photo - Clusters appear all along a fruiting branch.
Above: 1st photo - The pale yellow-green 5-part flowers which spring from a leaf axil in a cluster (a fascicle). The calyx is hemispheric shaped (bell shape in flower) with the lower part of the sepal lobes green and upper part yellowish. 2nd photo - The mature fruit is a glossy black 1/4 inch drupe, which is first green, then red before turning black.
Below: 1st photo - Fruit in the red stage before turning black. 2nd photo - the flattened nutlets, usually 2 to each drupe, about 5 to 6 mm long.
Below: It is common to find drupes in all color stages on a branch.
Below: 1st photo - The leaf has smooth, but sometimes wavy margins and 5 to 10 pair of sunken lateral veins that curve toward the pointed tip. 2nd photo -the leaf underside is more pale in color with raised veins.
Below: 1st photo - Older larger stems are grayish-brown with raised lenticels. 2nd photo - Young stems are gray-brown to reddish-brown with conspicuous light colored lenticels.
Notes: Eloise Butler, on June 14, 1922 made the following note in her log: Found full grown Rhamnus frangula [Frangula alnus]. Probably introduced on May 16, 1913 from Kelsey’s Nurseries in place of Rhamnus alnifolia [Alderleaf Buckthorn]". Glossy Buckthorn is found in the U.S. in the NE quadrant from Minnesota eastward, south as far as Tennessee and West Virginia plus a few western states. In Canada it is found from Saskatchewan eastward except Labrador and Newfoundland. It is listed as a prohibited or restricted noxious weed in five states, including Minnesota. Within Minnesota it is known in the metro area counties plus Wabasha, Houston and St. Louis. It is native to Europe, Northern Africa and Asia and it was first collected in North America in 1898 in London, Ontario. It has spread via the nursery trade which provided it as an ornamental, similar to the other invasive Common Buckthorn - Rhamnus cathartica.
Like the latter species, Glossy Buckthorn is kept under control by the Garden Staff.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"