It is a deciduous large shrub or small tree growing to 5 m tall, with blackish bark and dense, stiff, spiny branches. The leaves are oval, 2–4.5 cm long and 1.2–2 cm broad, with a serrated margin. The flowers are 1.5 cm diameter, with five slightly 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 mm diameter, black with a pale purple-blue waxy bloom, ripening in autumn, and harvested in October or November - usually after the first frosts. They are thin-fleshed, with a very strongly astringent flavour when fresh.