Rhamnus alnifolia L’Hér.
Alderleaf buckthorn is a North American native.
Identification: This small shrub reaches up to 3' (1 m) in height. Leaves are alternate, smooth-edged, elliptical, either rounded or pointed at the tip, up to 4" (10 cm) × 2" (5 cm). Flowers are yellowish-green, in groups of 1-3, nestled at the base of leaves, from May to July. Male and female flowers occur on different plants. Fruits are round, up to ¼" (6.3 mm) in diameter, turning to light red and then to deep black. Each fruit contains three seeds.
Edibility: Not edible.
Here are some similar-looking buckthorns:
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|Plant||This smaller shrub reaches up to 3' (1 m) in height.||Plants are rounded shrubs or small trees up to 33' (10 m) in height, with trunks that sometimes reach 10" (25 cm) in width. Outer bark is dark gray, while the inner bark is yellow and the heartwood is pink to orange in color. Stem tips are often tipped with a spine.||9½-20' (3-6 m) tall. It usually has multiple stems, rarely only one, becoming a tree. Dark brown-black bark covers a light yellow interior bark.|
|Flowers||Yellowish-green, 5-petaled, in groups of 1-3, nestled at the base of leaves, from May to July. Male and female flowers are on different plants.||Yellowish-green, with four petals, in dense clusters.||¹/₁₆-³/₁₆" (3-5 mm), 5-petaled, yellowish- or greenish-white, and inconspicuous.|
|Leaves||Alternate, elliptical, either rounded or pointed at the tip, smooth-edged, up to 4" (10 cm) × 2" (5 cm).||Elliptic (roughly oval), with several prominent veins roughly parallel to the leaf edges and fine teeth. They are ⅞-3½" (2.5-9 cm) × ⅜-1¼" (1.2-3.5 cm) in size. Leaves are mostly opposite, occasionally alternate, smooth on top and bottom.||Roughly oval, 1-2½" (3-7 cm) long and ⅞-1½" (2.5-4 cm) wide. Leaves have smooth edges and prominent veins and stems ¼-½" (8-15 mm) long.|
|Fruit||Round, up to ¼" (6.3 mm) in diameter, turning to light red and then to deep black. Each fruit contains three seeds.||Fruits are dense clusters of black berries ⅛-⅜" (6-10 mm) in diameter. Each berry contains 3-4 seeds.||Clusters of shiny black berries, reddish or purplish before ripening, are each ⅛-⅜" (6-10 mm) in diameter.|
The U.S. Geological Survey's Northern Prairie Wildlife Research Center
The USDA Plants Database
Ontario Trees & Shrubs
The Lady Bird Johnson Wildflower Center
The USDA Forest Service's Fire Effects Information Database
The Plant Conservation Alliance’s Alien Plant Working Group Least Wanted List
The University of Wisconsin's Robert W. Freckmann Herbarium
The Wisconsin Department of Natural Resources (Rhamnus lanceolata ssp. glabrata)
The Jepson Manual
Petrides, George A., Peterson Field Guides: Trees and Shrubs, Houghton Mifflin Co., 1972, p. 266
Rhamnus alnifolia description by Thomas H. Kent, last updated 25 May 2020.