Blackthorn

Appearance

''Prunus spinosa'' is a large deciduous shrub or small tree growing to 5 metres tall, with blackish bark and dense, stiff, spiny branches. The leaves are oval, 2–4.5 centimetres long and 1.2–2 centimetres broad, with a serrated margin. The flowers are about 1.5 centimetres in diameter, with five creamy-white petals; they are produced shortly before the leaves in early spring, and are hermaphroditic and insect-pollinated. The fruit, called a "sloe", is a drupe 10–12 millimetres in diameter, black with a purple-blue waxy bloom, ripening in autumn and harvested – traditionally, at least in the UK – in October or November after the first frosts. Sloes are thin-fleshed, with a very strongly astringent flavour when fresh.

Blackthorn usually grows as a bush but can grow to become a tree to a height of 6 m. Its branches usually grow forming a tangle.

''Prunus spinosa'' is frequently confused with the related ''P. cerasifera'' , particularly in early spring when the latter starts flowering somewhat earlier than ''P. spinosa''. They can be distinguished by flower colour, pure white in ''P. spinosa'', creamy white in ''P. cerasifera''. They can also be distinguished in winter by the shrubbier habit with stiffer, wider-angled branches of ''P. spinosa''; in summer by the relatively narrower leaves of ''P. spinosa'', more than twice as long as broad; and in autumn by the colour of the fruit skin purplish black in ''P. spinosa'' and yellow or red in ''P. cerasifera''.

''Prunus spinosa'' has a tetraploid set of chromosomes.

Naming

The specific name ''spinosa'' is a Latin term indicating the pointed and thornlike spur shoots characteristic of this species. The common name "blackthorn" is due to the thorny nature of the shrub, and possibly its very dark bark: it has a much darker bark than the white-thorn , to which it is contrasted.

The word commonly used for the fruit, "sloe", comes from Old English ''slāh'', cognate with Old High German ''slēha'', ''slēwa'', and Modern German ''Schlehe''. Other cognate forms are Frisian and Middle Low Germanhistorically spoken in Lower Saxony. ', Middle Dutch ''slee, slie, sleeu''; Modern Dutch ''slee''; Modern Low German ''slee''/''slē'', ''slī''; Danish ''slåen''.

The names related to 'sloe' come from the common Germanic root ''slaihwō''. Compare Old Slavic, Bulgarian, Macedonian, Ukrainian and Russian слива , West Slavic / Polish ''śliwa''; plum of any species, including sloe ''śliwa tarnina''—root present in other Slavic languages, e.g. Croatian/Serbian ''šljiva'' / шљива.

Habitat

The foliage is sometimes eaten by the larvae of Lepidoptera, including the small eggar moth, emperor moth, willow beauty, white-pinion spotted, common emerald, November moth, pale November moth, mottled pug, green pug, brimstone moth, feathered thorn, brown-tail, yellow-tail, short-cloaked moth, lesser yellow underwing, lesser broad-bordered yellow underwing, double square-spot, black hairstreak, brown hairstreak, hawthorn moth and the case-bearer moth ''Coleophora anatipennella''. Dead blackthorn wood provides food for the caterpillars of the concealer moth ''Esperia oliviella''.

The pocket plum gall of the fruit caused by the fungus ''Taphrina pruni'' produces an elongated and flattened gall, devoid of a stone.

Uses

The fruits are used to make sloe gin in Britain and patxaran in Basque regions. The wood is used to make walking sticks, including the Irish shillelagh.