The common name of this small thorny tree or bush is due to the fact that its bark has a much darker hue than that of the Hawthorn, which is also known as 'Whitethorn'.
'Spinosa' refers to the long spiny thorny shoots on the tree

The Blackthorn is possibly one of the commonest European shrubs. It grows from the British Isles, throughout Europe, into Western Siberia on any soil, except for wet and acid peat-bogs. We are able to find it almost anywhere in Britain, but in the North of Scotland it is more thinly spread.
Look for it in hedges, in clearings, on the edges of woodlands, on the edges of neglected farmland, on dry slopes and waste land. Wherever its colonising habit is allowed to continue without human interference, it will grow dense thickets, which form natural tree nurseries for larger tree species, who will eventually outgrow the Blackthorn.

General Appearance
A thorny shrub or small tree of 1-4 metres height. It often has more than one main stem, due to the rapid spread of the roots and the growth of suckers from these roots. The branches are stiff and rigid and usually thick set with many closely intersecting twigs, which make it rather impenetrable. On close examination, we find many spiny dwarf shoots on the branches, i.e. the shoots terminate into a hardened thorn. The branches, buds and leaves are arranged spirally in an 'alternate' (as opposed to 'opposite') fashion.

The winter twigs are very alike to Hawthorn, but the bark is smoother and darker, sometimes almost black and often with a slate-grey hue or greenish hue. The branches may may also have a reddish-brown to purple hue and have tiny lenticel spots on them. New shoots have closely crowded, velvety hairs on them, but these are soon lost. The tiny, nearly elliptical leaf-scar generally shows three dots, where the leaf-trace bundles were attached.

The leaves appear after the flowers have faded, usually in April. The leaves are small and pointed oval to nearly lanceolate in shape on short stems. The size is about 2-4 cm long. The colour is dull-green and there are tiny hairs on the veins underneath the leaves. The edges of the leaf are very finely and irregularly toothed. The central vein gives off 6 or more pairs of weak secondary veins, which break up near the margin into tertiaries. In Autumn the leaves may turn yellow and red.

The white flowers appear early in the year (from end February to April, depending on location) on the bare branches. They have a 5 lobed calyx and 5 white petals 5-8 mm long. Remember again, that the 5-petalled flowers are a distinguishing feature of the Rose family. These hermaphrodite flowers can appear single, in pairs or in close clusters on a small stalk. There are about 20 stamens, white with an orange head, clustered around a central green pistil with a yellow head. All these little stamens reaching out gives the flowers a happily ragged appearance. The pistils are ripe before the stamens, so self-fertilisation is avoided. The flowers contain nectar and have a subtle sweet smell to attract the insects on which it depends for pollination.

By the end of June the smooth green berries are virtually full-size, about 1 cm across. By Mid-August the colour changes to a purplish dark-blue with a misty bloom over its skin, although the astringent flesh inside stays green. Each sloe berry has one central stone or seed. The sloes ripen in September to October.

The Blackthorn grows long spreading roots, which send up shoots, known also as suckers, which will quickly grow into healthy young trees. The easiest way to propagate the Blackthorn therefore, is to dig up some of these baby trees, including a bit of the root and plant these out where you want the tree to grow.
Alternatively, the sloe can be harvested and seeded. Plant straight after picking and cover with about 1 cm of soil.