Two Oaks, One Woodland

There is a good chance that the stout, broad-shouldered tree you are leaning against in an old British wood is a native oak. We have two, and they are not difficult to tell apart once you know which details to look for. The pedunculate oak (Quercus robur) — often called the English oak — and the sessile oak (Quercus petraea), the tree that gives so much of upland Wales, the Lake District and the Scottish Highlands their character.

The two hybridise freely, so you will meet trees that sit awkwardly between them. Rather than worrying about that, get into the habit of checking three or four features at once: leaf stalks, leaf bases, acorn stalks and bark. Two out of three in agreement is a confident identification, and the looking itself is half the pleasure.

Reading the Leaves

From late April or May through to October, leaves are the simplest place to begin. Both species carry the familiar lobed, wavy-edged foliage, but the join between leaf and twig tells the story.

• Pedunculate oak: the leaf stalk is barely there, typically 2–5mm, and the base of the leaf has small ear-like lobes, called auricles, that clasp the stalk.
• Sessile oak: a distinctly longer stalk, usually 10–25mm, with the leaf base tapering smoothly into it in a wedge, no ears.

Secondary clues help. Sessile oak leaves tend to be more evenly and deeply lobed, slightly thicker and more leathery, with a darker, glossier upper surface. Pedunculate leaves are a touch paler, more papery and more irregular in their lobing. Do check leaves on sunlit, mature growth rather than shaded shoots lower down, which can be misleadingly large and soft on either species.

Acorns and Their Stalks

Late August to October is acorn time, and this is where the names earn their keep. Pedunculate means "with a stalk": the acorns hang from long, slender stems, often two or three to a stalk, dangling clear of the twig. Sessile means "sitting": the acorns are attached directly to the twig with no stalk at all, usually singly or in pairs, tucked close to the wood.

The cups differ too. Sessile oak cups have flatter, neater scales; pedunculate cups are knobbier and rougher. Acorn crops vary enormously year to year — a heavy "mast" year can carpet a wood — and that abundance feeds jays, grey squirrels, wood pigeons, deer and mice, which in turn scatter and bury the next generation of oaks. Look out too for galls on the acorns: the sticky, ridged knopper gall is common on pedunculate oak, while oak apples and spangle galls decorate the leaves of both.

Bark, Buds and Winter Twigs

Once the leaves are down, bark and buds take over. Mature pedunculate oak has deep, chunky fissures and heavy, knobbly ridges, a grey-brown hide that looks almost wrestled into place, often with burrs and hollows. Sessile oak bark is usually greyer and smoother for longer, breaking into flatter plates with finer, more regular vertical cracks rather than deep gnarled ridges.

Buds are a reliable winter check. Pedunculate buds are rounded and blunt, clustered at the twig tips in a soft brown knot. Sessile buds are more pointed and oval, arranged around the tip in a loose rosette. Beware of judging on bark alone: young trees of both species look smooth and grey, and hybrids blur the edges further.

Following the Seasons Through the Wood

Habitat gives the final nudge. Pedunculate oak favours heavy, damp lowland clays and is the classic hedgerow and parkland tree of southern and central England — if you are looking at an oak in a field boundary or a village green in the lowlands, it is very likely this one. Sessile oak prefers lighter, drier, more acidic soils and is at home on slopes and rocky ground, especially in the west and north.

• Winter: bare trunks show their architecture. Check bark texture and bud shape while the wood is quiet and open.
• Spring: oak comes into leaf after the ash in most years, and the new foliage opens in a lovely bronze-pink flush before greening.
• Summer: use the leaves and the shade; sit a while and compare several trees rather than one.
• Autumn: hunt for acorns and note whether they hang or sit. Leaf litter smells warmly of tannin underfoot.

A Slower Kind of Noticing

Learning a tree is a form of gentle attention, and attention is what most of us are short of. Choose one oak near a route you walk often and visit it through the year. Note the date its leaves open, when the first acorns drop, how the bark looks wet and black in February against how it glows in low autumn sun. That small habit — three details, written down or simply held in mind — does more for a sense of calm than any amount of rushing past.

Oaks repay this patience. A single ancient tree can support hundreds of species of insects, lichens, fungi and birds, and some of our oldest have stood for eight centuries or more. Take a flask, walk slowly, and let one tree become familiar. The wood will feel different from then on.