Alder Buckthorn: Berries, Bark & Brimstone Butterfly

In moist birch or alder woodlands, along the edges of bogs and wetlands, you will often find a small shrub with dark, almost black stems speckled with light dashes and glossy, smooth-edged leaves. By late summer, its branches simultaneously display green, red, and black berries. This is the alder buckthorn (also known as glossy buckthorn)—a plant with a long history of medicinal use, highly valued by bees, birds, and one of Europe's most beautiful butterflies. In this Tree Guide profile, you will learn how to identify alder buckthorn and why you should never snack on its fruit.

Latin Name	Frangula alnus (syn. Rhamnus frangula)
Family	Buckthorn (Rhamnaceae)
Group	Deciduous shrub or small tree
Height	10–20 ft (3–6 m), sometimes up to 23 ft (7 m); trunk up to 8 inches (20 cm)
Blooms	Late spring to midsummer
Berries	0.2–0.4 inches (6–10 mm), green → red → black, ripening late summer to early fall
Habitat	Moist forests, thickets, riverbanks, wetlands, and bogs
Safety	Fresh bark and berries are strong laxatives and mildly toxic—do not eat

How to Identify Alder Buckthorn

Alder buckthorn typically grows as a multi-stemmed shrub, and much less frequently as a small tree with a trunk up to 8 inches (20 cm) across. In richer soils, it grows taller and more upright, while in poor soils, it remains shorter and more heavily branched. Unlike its relative, the common buckthorn, alder buckthorn has no thorns. Its reddish-brown shoots are quite brittle—in fact, its botanical genus name, Frangula, comes from the Latin word for "to break."

Leaves

The leaves are arranged alternately and are ovate or elliptic, measuring 1.2–2.8 inches (3–7 cm) long. They are dark green, glossy, and have smooth, untoothed edges. Their most distinctive feature is the 6 to 10 pairs of prominent, indented veins that curve gracefully toward the leaf tip. From a distance, alder buckthorn leaves somewhat resemble those of the black alder, but alder leaves have toothed edges and a blunt or notched tip. In autumn, alder buckthorn foliage turns yellow.

Flowers

The flowers are tiny, about 0.1–0.2 inches (3–5 mm) across, star-shaped, and feature five greenish-white pointed petals. They are bisexual and cluster in groups of two to seven in the leaf axils, making them quite inconspicuous. Alder buckthorn has a long blooming period stretching from late spring through midsummer. Because of this extended flowering time, the blossoms are heavily visited by bees, making the shrub highly valued by beekeepers.

Berries

The fruit is a round, fleshy drupe about 0.2–0.4 inches (6–10 mm) in diameter, containing two to three seeds. The berries ripen gradually: they start out green, turn a vibrant raspberry red in late summer, and finally mature to dark purple or black by early fall. As a result, it is very common to see green, red, and black berries on the exact same bush at the same time. Birds, especially thrushes, eagerly eat the fruit and help distribute the seeds.

Bark

The bark is smooth and dark grayish-brown to almost black, heavily speckled with numerous light horizontal dashes called lenticels. If you cut or scrape away the top layer, you will reveal a bright lemon-yellow inner bark, while older bark develops a red corky layer underneath. This distinctive bark makes alder buckthorn easy to identify even in the dead of winter.

Alder Buckthorn, Common Buckthorn, or Alder?

Feature	Alder Buckthorn (Frangula alnus)	Common Buckthorn (Rhamnus cathartica)	Black Alder (Alnus glutinosa)
Thorns	None	Present	None
Leaves	Smooth-edged, glossy, curved veins	Finely toothed	Toothed, blunt or notched tip, sticky
Flowers	Bisexual, 5-parted	Unisexual, 4-parted	Catkins
Fruits	Red, then black berries	Black berries	Woody, cone-like strobiles
Form	Shrub or small tree, 10–20 ft (3–6 m)	Shrub or small tree	Tree

Alder buckthorn often grows alongside black alders and birches—read more about them in our alder and birch profiles.

The Brimstone Butterfly and Alder Buckthorn

In early spring, as soon as the weather warms, one of the first butterflies to take flight in Europe is the bright yellow brimstone butterfly (Gonepteryx rhamni). Its caterpillars feed exclusively on the leaves of just two plants: the alder buckthorn and the common buckthorn. Consequently, these butterflies can only breed where these specific shrubs grow. Females lay their eggs on the undersides of young leaves, usually on isolated, sunlit bushes. Adult butterflies spend about seven months overwintering in woodlands before returning to the buckthorns in spring. In Europe, alder buckthorn is sometimes planted specifically to attract brimstones. However, in North America—where it was introduced roughly 200 years ago—it has escaped cultivation and is now widely considered an invasive species.

Alder Buckthorn Bark: Medicinal Uses

Alder buckthorn bark is a well-known traditional medicinal ingredient. It contains 3–7% anthraquinones, which are compounds with a strong laxative effect. The European Medicines Agency's Committee on Herbal Medicinal Products recognizes that alder buckthorn bark preparations can be used short-term for occasional constipation in adults and adolescents over 12 years of age, for no longer than one week. They should not be used by children under 12, pregnant or breastfeeding women, or anyone suffering from intestinal obstructions or unexplained abdominal pain. Overdosing can cause abdominal pain, cramps, and diarrhea, while prolonged use can lead to pigmentation of the intestinal lining.

It is crucial to know that fresh bark is toxic: the compounds it contains cause severe vomiting and diarrhea. Therefore, bark stripped from young stems in early spring must be dried and aged for at least one full year, or heated at 212°F (100°C) for an hour, which breaks down the toxic compounds. Preparing this raw material yourself is risky, so it is much safer to choose commercially available pharmacy preparations and consult a pharmacist or doctor before use.

Wood, Charcoal, and Dyes

Alder buckthorn wood is a brownish-orange color; it has historically been used for woodturning, decorative veneer, and in the past, for shoe lasts and wooden nails. Burning the wood produces a nearly ashless charcoal that was once considered the finest material for making gunpowder and was highly prized for fuses due to its exceptionally even burn rate. Additionally, a yellow dye can be extracted from the bark, and a green dye from the unripe berries. We cover other small woodland shrubs and trees in our hazel, rowan (mountain ash), and hawthorn profiles.