Blackthorn (Prunus spinosa L.)

Text and top photo by Linn Borgen Nilsen. 

Blackthorn or sloe belongs to the rose family and is a deciduous shrub, native to Europe, Western Asia and Northern Africa. Its dark blue fruits – sloes – tastes bitter if eaten raw. Nevertheless, the species has a long history of diverse use and is currently cultivated both as an ornamental plant and for fruit production.

Blackthorn occurs in most of Europe, including in Denmark, southern Sweden and along the southern coast of Norway. In Finland, wild specimens have only been observed in the south-western archipelago. In Scandinavia the species is normally 1-2 m tall and commonly found in forest margins, on meadows and pastures and on rocky slopes. Especially in coastal areas, it is often found to form dense, impenetrable scrubs.

A population of Blackthorn can be a beautiful sight in early spring, as they can dominate the landscape with white flowers. The flowers appear before the leaves, often as early as in March. You do not want to come too close to a Blackthorn bush though. As the name suggest, it is characterized by dark and thorny branches. In fact, the species name “spinosa” comes from the Latin word spina, which means thorn. Its intimidating appearance is perhaps one of the reasons why Blackthorn is said to have been associated with dark witchcraft.

The dark blue fruits of the Blackthorn trees (called sloes) are edible but have a very bitter and astringent flavor. Despite the lack of sweetness, sloes are used for many different purposes, such as to produce jelly, syrup and liqueurs. Sloe Gin, an alcoholic beverage where gin is infused with sloes and sugar, is perhaps the most famous. Collection of sloes is normally done in September or October, preferably after the first frosty night.

Wide Range of Use

Blackthorn has been planted and associated with gardens since the Middle Ages. Historically, it was a commonly used plant in folk medicine, for instance to soothe colds and respiratory diseases, constipation, bloating and bladder problems. Both flowers, petals and leaves were used to make teas and other remedies. The bark of the Blackthorn was also used to make ink and tan leather. It was also common practice to use Blackthorn bushes as «living fences», preventing domestic animals from escaping.

Still today, Blackthorn is cultivated and sold, both for fruit and for ornamental purposes. As an early flowering plant, Blackthorn provides an important source of nectar and pollen for insects in spring, and the dense bushes can offer hideouts for birds and other small animals.

Several species are related to Blackthorn, the most well-known being plum (Prunus domestica) and wild cherry (Prunus avium). As with most Prunus species, also Blackthorn hybridize easily. Due to the occurrence of cultivated populations and their escapes, the genetic variation within Prunus spinosa is rather complex.

In addition to its direct use, wild populations of Prunus spinosa can harbour genetic diversity which allows the further development and adaptation of domesticated species. As a relative to economically important crops, it is relevant to further study the species and to ensure appropriate management and conservation of particularly important populations.

References:

Fremstad, E., Bjorå, C. S., Elven, R., Hegre, H., and Solstad, H. 2022. Norsk flora. Samlaget.

Hanelt, P.. 1997. European wild relatives of Prunus fruit crops. Bocconea 7.

Popescu; I. and Caudullo, G. 2016. Prunus spinosa in Europe: distribution, habitat, usage and threats. s. In: San-Miguel-Ayanz, J., de Rigo, D., Caudullo, G., Houston Durrant, T., Mauri, A. (Eds.), European Atlas of Forest Tree Species. Publ. Off. EU, Luxembourg.

Prunus spinosa L. Plants of the World Online. Royal Botanic Grdens, Kew. Retrieved 15 November 2023. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:730297-1

Rhodes, L. and Maxted, N. 2016. Prunus spinosa. IUCN Red List of Threatened Species. https://www.iucnredlist.org/species/172194/19400568 Retrieved 1 November 2023.

Sloe gin. Wikipedia. https://en.wikipedia.org/wiki/Sloe_gin Retrieved 15 November 2023.

Van Wyk. 2005. Food plants of the world: An illustrated guide.

Zohary, D. and Hopf, M. 1993. Domestication of plants in the Old World, 2nd ed. Clarendon Press, Oxford.