Frangula alnus
Common names: Alder Buckthorne, glossy buckthorn, breaking buckthorn, black dogwood or glossy or fen buckthorn
Irish name: Draighean fearna
Latin name: Frangula alnus
Family: Rhamnaceae
Origin: Native
Tree type: Deciduous broadleaf tree
How it looks
Shape, bark, twigs
Mature trees can grow to a height of 6m. The outer bark is blackish brown, with the inner bark being bright yellow when exposed. The bark on young shoots is smooth and green, becoming purple-brown in colour and having fine white streaks.
Buds
The buds on the stem are arranged alternately and covered in hairs.
Leaves
Alder Buckthorn has alternately arranged, untoothed oval leaves with wavy margins. These dark green, glossy leaves are 3–7cm long, with a rounded tip which narrows toward the stalk. The leaf surface is hairless above and somewhat downy beneath, especially when young. The leaves have 6–10 pairs of lateral veins that do not curve towards the tip. They turn yellow in autumn.
Flowers
Clusters of small flowers bloom in May and June in the leaf axils of upper leaves (the space between the branch and leaf). The star-shaped flowers are small and have a diameter of 3-5mm. They consist of five greenish-white triangular petals and five sepals. Alder buckthorn is a hermaphrodite, meaning that male and female reproductive parts are within the same flower. These flowers produce nectar secretions which attract bees, wasps, and flies for pollination.
Fruits
Following pollination by insects, the flowers develop into small berries, which ripen from green to red in late summer and eventually to a glossy dark purple or black in early autumn. The round berries are 6-10mm across and contain two- or three seeds. Birds are the main dispersers of seeds, but other potential ways of dispersal include small mammals, gravity and water. The fruits can float for up to two weeks in freshwater, which helps to spread them around lake shores and along rivers.
Similar species
The alder buckthorn is similar in appearance to the buckthorn, Rhamnus catharticus, but can be distinguished from one another by their leaves. The buckthorn has opposite leaves with toothed margins and sharp thorns, while the Alder buckthorn has alternate leaves with wavy margins and no thorns.
Where to find it
Alder Buckthorn is a rare native tree to Ireland, that can be found mainly in Counties Galway and Clare. It thrives in damp, peaty soil, limestone pavement, and rocky lake shores but avoids drought-prone and permanently waterlogged conditions, as well as heavy shade in woodland.
This tree is a light-demanding pioneer species that grows well in scrub, hedgerows, wet heathland, riverbanks and bogs. It is also present in other parts of Europe, northernmost Africa, and western Asia, and can grow from 0 to 2,000 m above sea level.
Cultural importance
History
The discovery of Alder Buckthorn charcoal samples during the archaeological excavation of burnt mounds or fulachta fiadh (ancient outdoor cooking sites) in the Irish midlands demonstrate that it was used by prehistoric communities for firewood during Bronze Age (c. 2500 – 800 BC). It is known for producing high quality charcoal and has been found at a number of prehistoric sites throughout Ireland. Alder Buckthorn roundwood and timbers were also found preserved as part of a Bronze Age bog trackway at Cooleeny, County Tipperary, showing that it was occasionally used to build structures during this period.
Despite its apparent value in earlier periods, Alder Buckthorn does not appear on the early Medieval (c. 400 – 1100 AD) tree lists and is not included in either the ‘Commoners’ or ‘Lower Divisions of the wood’. It is presumed that this was because it was not considered of great economic value at the time. This view clearly changed in later periods, as Alder Buckthorn charcoal became highly valued for its use in the production of gunpowder. Indeed, the tree was specifically coppiced for this purpose. It’s bark and berries were used in the dying of fabrics, and its branches are still used to build beehives. Likewise, the straight shoots from coppiced Alder buckthorn have been used in making walking sticks, umbrella handles, wooden pegs, and butcher's skewers. Due to its hardness, durability, and sharpness, it has also been used in the production of wooden nails, shoes, shoe lasts, and arrows.
Myth, Legend and Folklore
There is no known reference to Alder Buckthorn in Irish myth and folklore. However, in other countries, it was viewed as a malignant tree. Eoin Mac Coitir suggests that this may be why there is so little folklore surrounding it. At the same time, it was used in certain contexts to protect against evil, as in Athens, Greece, where Alder Buckthorn was placed across one’s doorway to prevent the entrance of spirits who were thought to have risen during the Commemoration of the Dead. Another account purports that the spirit of the Alder Buckthorn could be called forth to help manage depression and anger.
Value to wildlife
The flowers of Alder Buckthorn are highly beneficial for pollinators like bees and flies. The fruit of this plant is a significant source of food for birds, especially thrushes, and various mammals. Additionally, the leaves of Alder Buckthorn serve as the primary food plant for the brimstone butterfly.
Threats
The alder buckthorn is a tree that is usually not affected by any major pests or diseases. However, it is one of the rarest native trees in Ireland and its population has suffered a decline due to various factors such as wetland drainage for agriculture, loss of habitat due to peat-cutting, and nutrient enrichment. If you want to assist in the preservation of this species, you can submit your sightings on the National Biodiversity Centre website.
To learn more about threats to Irish trees, visit ‘Threats to Trees.’
Uses
The bark of the alder buckthorn is one of the ingredients used in an herb-based alternative treatment for cancer. For hundreds of years, the alder buckthorn has been used in folk medicine for its laxative effects.
Alder buckthorn charcoal is still highly valued in the manufacturing of gunpowder and is considered the best. It continues to be used in Swiss black powder for fireworks, blast fuses, and military applications.
The alder buckthorn tree can produce various dyes. Its bark and leaves can be used to make a yellow dye, while its ripe berries can produce a blue or grey dye. Additionally, the unripe berries can be used to create the artist's colour 'Sap Green'.
It is a good urban tree due to its pollution tolerance.
References
Gowen, M., Phillips, M. and Ó Néill, J. (Eds.). 2004. The Lisheen Mine Archaeological Project 1996–98, Published on behalf of Margaret Gowen & Co. Ltd. Bray: Wordwell.
MacCoitir, N. 2015. Ireland’s Trees: Myths, Legends and Folklore. Cork: The Collins Press.
Milner, E. 2011. Trees of Britain and Ireland: History, Folklore, Products and Ecology. London: Natural History Museum.
Nelson, E. C. and Walsh, W. 1991. Trees of Ireland. Dublin: Liliput Press
O’Carroll, E. 2010. Ancient Woodland Use in the Midlands: Understanding Environmental and Landscape Change through Archaeological and Palaeoecological Techniques, In: Creative minds, Production, Manufacture and Invention in Ancient Ireland. NRA Monograph Series issue 3.
Tree Council of Ireland. 2023. Buckthorn (Alder). Tree Council of Ireland Website. BUCKTHORN - (Alder) (treecouncil.ie)
Warner, D. 2012. Buckthorn tree? There are three, Irish Examiner. https://www.irishexaminer.com/opinion/columnists/arid-20214332.html
Stroh, P. A., Humphrey, T. A., Burkmar, R. J., Pescott, O. L., Roy, D. B., & Walker, K. J. 2023. BSBI Online Plant Atlas 2020. https://plantatlas2020.org/atlas
Tree Council of Ireland. 2024. Native Irish Trees. Tree Council of Ireland. https://www.treecouncil.ie/native-irish-trees
Woodland Trust. 2024. A-Z of British trees. Woodland Trust. https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/british-trees/a-z-of-british-trees/