Oak (Quercus spp.)
Flowering: April - May
The tree may reach up to 50 meters height. The leaves are multi-lobate. The oak bark is greyish and mildly fissured in length. The flowers appear after the leaves. The yellowish male flowers are clustered in long pending catkins (about 10 cm), whereas female flowers are very small and terminal or springing from the axils of the leaves. The oak fruit is a nut, called acorn, placed into a cupule.
In Belgium, two species are commonly found in forests : the English oak (Quercus robur) and the Irish or sessile oak (Quercus petraea).
The oak pollen may cause respiratory allergies.
Cross-reactive allergy: there is cross-reactivity between the Fagaceae pollens (sweet chestnut, beech and oak) and the Betulaceae pollens (alder, birch, hornbeam and hazel).