At a glance
Essentials
- Size
- It can reach about 40 m in height. The range may vary with age, sex and population.
- Distribution
- Its native range extends across Europe to Iran. In Ireland, it is commonly found in the Midlands; in Great Britain, it is especially common in the central and southern regions.
- Habitat
- It grows in the temperate biome. In Ireland, it is particularly associated with heavy lowland soils and damp places near rivers, where the ground can support wet soils in winter.
Observation guide
What to look for
- 01
Lobed leaves about 10 cm long, with four or five pairs of deep, smooth-edged lobes and two small “ears” at the base.
- 02
Very short or absent leaf stalks, while the acorns hang from long stalks.
- 03
Reddish female flowers, clustered and resembling small buds near the tips of the twigs, on long stalks.
- 04
Rounded buds in clusters towards the ends of the shoots; they are small and hairless.
Lighting, age and viewing angle can hide features. If identification affects consumption, handling or conservation, consult specialist sources.
Ecology
Description and characteristics
Form and bark. Quercus robur is a deciduous tree that can reach about 40 m and develop a broad, spreading crown supported by robust branches. Its bark is greyish brown: smooth when the tree is young, becoming rougher and marked by vertical ridges with age. The buds are alternate and clustered towards the ends of the shoots; they are small, about 3–8 mm long, hairless, and have fewer than 20 scales. The leaves, about 10 cm long, have four or five pairs of deep lobes with smooth edges. Their stalks are absent or very short, and they have two basal lobes resembling small “ears.”
Flowers and pollination. Male and female flowers occur on the same branch. The male flowers form hanging, bright green catkins that release pollen carried by the wind. The female flowers are small clusters of modified leaves, resembling reddish buds, located near the tip of each twig and at the ends of long stalks. The flowers appear in early spring, before the leaves are fully developed; in Ireland, the foliage appears in April or May, about two weeks before that of the sessile oak, Quercus petraea. This seasonal difference applies to Ireland, not to the entire range.
Fruits and life cycle. After pollination, the female flowers develop into acorns; the Irish source places their formation in September. Each acorn contains a seed within a hard outer casing and grows in a cup on a long stalk. Young acorns are green and turn brown as they ripen; in the British context, they are described as falling and being able to germinate the following spring. Fallen leaves decompose and form a layer of leaf litter that benefits invertebrates and fungi. The tree also provides food and shelter for many organisms: its acorns are eaten by birds and mammals, while its branches, trunk, cavities, and dead wood can provide support, shelter, or nesting sites. It can live for around a thousand years.