You can tell the two types apart by looking at their acorns. Sessile acorns are stubby and have no stalks (sessile means ''stalkless''), while the acorns of English oaks are longer, with long stalks (pedunculate means "stalked"). Confusingly, Pedunculate oak trees have unstalked leaves while the Sessile's leaves have stalks.

The shape of the trees is also different. Sessile oaks have straighter trunks and branches, and high, fan-shaped crowns. Pedunculate oaks have wider, domed crowns, and thicker trunks at the base. Sessile oaks are often taller, reaching 130ft, compared with the 115ft of the tallest Pedunculates. These are among our oldest trees - they can survive for 1,000 years if their topmost branches are regularly lopped, a process called pollarding.

Oaks are wonderfully useful trees, and not just for timber. In the past, the oak's bark was used for tanning leather, and its branches turned into charcoal for iron-making. Oak apples (galls made by wasps) were turned into black ink, and acorns fed pigs in the forests throughout the winter.