- Name also: Sloe
- Family: Rose Family – Rosaceae
- Growing form and height: Shrub. 1–4 m (3–13 ft.).
- Flower: Regular (actinomorphic), strong-smelling, approx. 10–18 mm (0.4–0.6 in.) across. Calyx-lobes 5, elliptic, with membranous margins, hairless. Petals 5, white. Stamens almost 20. One carpel. Flowers solitary or in pairs, on thorn-tipped branches or short shoots.
- Leaves: Alternate on the annual shoot. Fairly small, short-stalked, with fine-toothed margins, greyish-green beneath, veins hairy.
- Buds: Broadly egg-shaped–cone-shaped, small, brown, usually three together.
- Fruit: Globose, blackish drupe with bluish bloom and large seed.
- Habitat: Rocky places, waysides, rock outcrops, dry meadows, coppices. Often on calcareous soils (calciphile).
- Flowering time: May–June. Flowers before coming into leaf.
- Endangerment: Near threatened.
Blackthorn is a densely branched, usually 2–3 m (6–10 ft.) tall shrub with long and sharp thorns. By means of root suckers it often forms impenetrable thickets which are excellent nesting places for birds and small mammals. Blackthorn flowers before coming into leaf in spring. The flowering is quick but showy. The flowers are insect-, especially beetle-pollinated.
Plum-like fruits ripen late. They are sour at first but become sweeter after the first frosts. Then they can be used e.g. for making squash or liqueur. Because fruits are rich in tannic acids they have a strong contractive effect on mucous membranes and, hence, have been used as medicine.
Blackthorn, also known as sloe, belongs the genus of cherries and plums (Prunus). The genus is quite large comprising close to 200 species. In Finland blackthorn occurs only in the Åland Islands and the south-western archipelago. It doesn’t thrive inland, shoot parts above the snow-line freeze.