Prunus spinosa L., Blackthorn

Account Summary

Growth form and preferred habitats

There can only be a few field botanists who have not drawn blood on this very common, rigid branched, sharply thorned deciduous shrub or small tree; indeed, the woody thorns have a reputation for causing septic wounds. Blackthorn or Sloe is one of the most abundant native shrubs and is particularly conspicuous in hedges and scrub when in bloom in early spring. In hedges, it is very commonly planted (in recent years sometimes with quicks of non-native, European origin), but in more mixed hedgerows it may be feral or bird-sown. The shrub grows rapidly to around 4 m and branches and suckers very strongly, forming wickedly dense thickets of dark blackish-brown branches, impenetrable to all grazing mammals larger than rabbits on account of its long, very hard, woody thorns and its dense, irregular branching (Edlin 1964; Rackham 1980, pp. 351-2). Such thickets can develop in a matter of a few years if ground is neglected and the shrub remains unchecked. Widespread in scrub woodland and hedgerows, it also colonises rocky ground, fens and sea cliffs, dunes and shingle.

P. spinosa reproduces by bird-dispersed seed and even more commonly by rapidly spreading vegetative suckers. P. spinosa colonises under-grazed pasture and waste ground, especially in the Fermanagh area on limestone. Having said that, it grows on a very wide variety of soils, avoiding only the most acidic, wet peat. On undisturbed rocky ground, it forms wickedly dense thickets impenetrable to all mammals larger than rabbits on account of its long, very hard woody thorns which strongly deter grazing, and its dense, irregular branching pattern (Edlin 1964; Rackham 1980, pp. 351-2).

In many areas, native stands are augmented by planted stock in hedges, or as anti-browser nurse plants in tree copse plantations, although Crataegus monogyna (Hawthorn) is generally the preferred and more readily available shrub for these purposes. While useful in such tree plantations, P. spinosa is not long persistent in secondary woodland, eventually being shaded out by taller trees. Larger Blackthorn trees cannot stand coppicing either, as cutting down to ground level generally, or very often, kills the plant (Rackham 1980).

Fossil history

Blackthorn is an insect pollinated tree or shrub and therefore does not form sufficient pollen for it to appear in the fossil record. However, macrofossil remains do appear as wood or fruit stones. Interestingly, although P. spinosa has been recorded in this way from early interglacials from the Cromer Forest Bed series to some stages of the Hoxnian and Ipswichian, it does not feature in the current Flandrian (Littletonian in Ireland) until the Mesolithic period when it frequently appears in archaeological sites, often as charcoal. It can be deduced from this that P. spinosa was used by early man as firewood, charcoal and for its edible fruit (eg a large quantity of fruit stones was found in a Glastonbury Lake Village deposit). In view of the earlier interglacial records, it is probably sensible to regard the absence of P. spinosa fossils from the early and middle Flandrian as more apparent than real (Godwin 1975, p. 196).

Flowering reproduction

P. spinosa flowers from March to late May, with a peak in April, the blossom opening well before the leaves appear. The 10-15 mm diameter axillary flowers are borne solitary or in twos or small clusters on short smooth pedicels. They have five pure white petals, around 20 stamens and a single green style and stigma projecting above the stamens. Nectar secreted by a disc on the saucer-like hypanthium is partially concealed at the base of the stamens. The flowers attract a wide range of insect visitors including bees, overwintering hoverflies, butterflies and early flies, but the very early blossom is rather often destroyed by late frosts in March and early April (Proctor & Yeo 1973; Pollard et al. 1974).

Fruit dispersal

The fruit is a fleshy drupe, a 3-layered structure with a central stone containing the single seed of the flower. They ripen in September, some shrivelling and soon dropping, others surviving in good condition well into the winter. Song Thrushes take more fruit than Blackbirds; the size of the sloe is close to the upper swallowing limit of the smaller members of the family. Robins and Starlings merely peck at the flesh rather than ingest and transport the fruit (Snow & Snow 1988, pp. 58-9).

Uses

Although difficult to collect on account of the ferocious thorns, the plum-like sloe fruit is still sometimes used to make jam, wine, or especially to flavour gin. Rackham (1980) mentions that P. spinosa charcoal and sloe stones have been found fossilised in archaeological sites of Mesolithic and later ages

Sloe juice and the inner bark are very strong astringents and the plant was used by herbalists for, "cooling, binding and drying" bleeding wounds, especially internally, including bowel ailments, piles and diarrhoea (Gent 1681). Sloe jelly is recommended for coughs and sore throats, sloe wine for colic and sloe gin for kidney problems (Lang 1987; Allen & Hatfield 2004).

"The lower branches of Blackthorn make hard and finely coloured walking or riding sticks with a very aristocratic knobbliness.", according to Mabey (1977). The knobbliness is thanks to the very numerous, thickly set, dwarf lateral branches that the thorns represent. The Irish 'shillelagh' is a prime example of the Blackthorn stick, its large knobby head being the base of the shoot where it comes off the root. As a formidable club weapon, it is euphemistically referred to as, 'an ancient Hibernian tranquilliser'. Up until the 18th century, tannin-rich Blackthorn bark was also used to make ink for writing. The tannin fixed the ink on the paper and prevented fading (Mabey 1977).

There are also a multitude of superstitions about Blackthorn, including bad luck associated with bringing it (white flowers) into a house when in blossom; it was considered (like Hawthorn) a premonition of death (Vickery 1995).

Fermanagh occurrence

Blackthorn, or Sloe, is the fifth most frequently recorded tree or shrub in Fermanagh, found throughout in 435 tetrads, over 82.4% of those in the VC.

British and Irish occurrence

Blackthorn is a very widespread and common shrub throughout B & I, absent only from the extreme W of Ireland and NW & Highland Scotland on account of the unsuitable sodden, strongly acidic peaty soils prevalent in those regions. It is also absent from the outer W & N Scottish isles, except for scattered introductions (New Atlas).

European and world occurrence

P. spinosa is native and widespread throughout Europe except the NE and beyond 60°N in S Sweden. It stretches across the continent from S Spain to Iran and SE Siberia and is present on all or most of the islands of the W Mediterranean. It is also introduced in eastern N America and New Zealand (Godwin 1975; Hultén & Fries 1986, Map 1178; Sell & Murrell 2014).

Threats

None.

• Find out more about the format of the species accounts
• View abbreviations
• View references for all species accounts
• View a gazetteer of all the sites