Alder buckthorn (Frangula alnus)

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Alder buckthorn is unrelated to alder. It's a colourful tree native to England and Wales, most of Europe, northern Africa and western Asia.

Common name: alder buckthorn

Scientific name: Frangula alnus
Family: Rhamnaceae

UK provenance: native

Interesting fact: the name alder buckthorn is thought to be derived from its similar appearance to alder and the fact that the two trees are often found growing together. Botanically the two species are unrelated, alder buckthorn is in the Rhamnaceae family and alder is in the Betulaceae (birch family).

What does alder buckthorn look like?

Overview: mature trees can grow to a height of 6m. The outer bark is dark brown but the inner bark is bright yellow when exposed. Unlike purging buckthorn, the branches and stems are smooth and thornless. The twigs are smooth and straight, purple-brown in colour and have fine white streaks. It is closely related to purging buckthorn (Rhamnus cathartica).

Leaves: narrower than those of purging buckthorn, matt green, oval, 3-7cm long and slightly hairy. They have a rounded tip but are tapered towards the stalk.

Flowers: unlike purging buckthorn, alder buckthorn is hermaphrodite, meaning that male and female reproductive parts are contained within the same flower. The star-shaped flowers are small, 3–5 mm diameter, with five greenish-white triangular petals. They appear in May to June in clusters in the leaf axils.

Fruits: once pollinated by insects, the flowers develop into a small berry, which ripens from green to red in late summer, eventually to a dark purple or black in early autumn. 

Look out for: the leaves are placed alternately along the twig and have 6-10 pairs of lateral veins that do not curve towards the tip.

Could be confused with: dogwood  (Cornus sanguinea) which is not spiny or purging buckthorn (Rhamnus cathartica) which has opposite as opposed to alternate leaves.

Identified in winter by: the buds do not have scales and are hairy. Peeling back the bark surface reveals yellow bark underneath.

Where to find alder buckthorn

Alder Buckthorn is native to most of Europe and spreads as far as western China. It grows best in wet soils and open woods, thriving in scrubs, hedgerows, wet heathland, river banks and bogs. Although it prefers acidic soils it can grow on neutral soils as well. It is widespread but rare.

Value to wildlife

Like purging buckthorn, alder buckthorn is the food plant of the brimstone butterfly, whose caterpillars eat the leaves. Its flowers provide a source of pollen and nectar for bees and other insects, and its berries are eaten by birds.

Mythology and symbolism

Like purging buckthorn, it was once used as a purgative, which was thought to help rid the body of illness and disease.

How we use alder buckthorn

A yellow dye is obtained from the leaves and bark. It is used in Russia and turns black when mixed with salts of iron. A green dye is obtained from the unripe fruit, and a blue or grey dye is obtained from the ripe berries.

Alder buckthorn charcoal is prized in the manufacture of gunpowder, and is regarded as the best wood for the purpose. It is particularly valued for time fuses because it has a very even burn rate.

Plants have horticultural value and can be grown as an informal hedge. The wood has been used to make wooden nails and shoe lasts.

Threats

There are no known threats, pests or diseases associated with alder buckthorn. 

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