Latin name: Quercus spp.
Plant description: Large trees with lobed leaves and grey bark with knobbly ridges. Groups of greenish-yellow catkins produce the pollen. Fruit: acorn. There are some evergreen species of oak with smaller, thick, smooth-edged leaves.
Distribution: UK: countrywide. Oak trees are native to Europe, Asia and the Americas.
Allergenicity and other health impacts: Approximately 20% of hay fever sufferers are allergic to oak pollen which has moderate allergenicity.
Season: April and May to early June, although the start of the season can vary by up to one month and often occurs about two weeks later in Scotland than in the rest of the UK. The peak of the season occurs in April in early seasons or in May in later ones.