Rhamnus alnifolia (Alder-leaved Buckthorn)
|Also known as:||Dwarf Alder, American Alder Buckthorn|
|Life cycle:||perennial woody|
|Habitat:||part shade; moist, shady bogs, fens, lake edges|
|Bloom season:||May - June|
|Plant height:||2 to 3 feet|
|Wetland Indicator Status:||GP: FACW MW: OBL NCNE: OBL|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Flowers are small, ¼ inch or less across, yellowish green, 5 pointed and star-like, short stalked, in clusters of 1 to 3 in the leaf axils of new growth. There are no petals, the triangular star points are sepals set around a flattened, saucer like recepticle. Male and female flowers are on separate plants, the male flowers with 5 yellowish stamens surrounding a green center, females with a 3-parted style in the center.
Leaves and bark:
Leaves are simple and alternate, oval or oblong lance-elliptic, 2 to 4½ inches long and ¾ to 2¼ inches wide, the edges with rounded teeth, with or without glands in the serrations, and 5 to 8 veins per side. The upper surface is darker green, appearing shiny or with sparse hairs; the lower surface is lighter green with hairs typically present.
At the base of the leaf stalk of new growth is a pair of narrow, leafy appendages (stipules). Main branching stems are horizontally spreading, typically less than 1 inch in diameter at the base with thin, roughish red-brown to gray bark. Side branches are erect, spindly, and thornless. New growth is green or brownish with minute hairs turning grayish brown the second year.
For all the negative press that buckthorns get, many people are surprised that Minnesota has a native buckthorn. While fairly widespread and common within its preferred habitats across the northern 2/3 of the state, as you'd expect with native species it is not invasive at all. It does produce a fruit with viable seeds that are likely eaten and spread by wildlife, but co-evolved factors limit its introduction and spread across the broader environment. A primary means of reproduction is by a process called “layering”, where the horizontal stems and branches produce roots, creating expanding colonies up to 50 feet across. The root/branch structures of these colonies may become disconnected over time producing genetically identical but independently functioning individuals within the colony. This native can be distinguished from the invasive non-native buckthorns by its short stature (3 feet or less at maturity), the obvious stipules at the base of the leaf stalk, 5-parted flowers, and leaves with rounded teeth and 5 to 8 veins per side. Glossy Buckthorn (Frangula alnus) has toothless leaves with 6 to 9 veins per side, and Common Buckthorn (Rhamnus cathartica) has 4-parted flowers and leaves with rounded teeth and only 3 or 4 veins per side. Both of the non-natives grow significantly taller and bushier than Alder-leaved Buckthorn, and their clusters have much more than 3 flowers and produce far more fruit.
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Photos courtesy Peter M. Dziuk taken in Aitkin, Becker, Lake and St. Louis counties.
Have you seen this plant in Minnesota, or have any other comments about it?