Hazel
Description
Hazel (Corylus avellana, family Betulaceae) is a deciduous multi-stemmed shrub or small tree of 3-8 m with smooth gray-brown bark. Leaves are simple, alternate, suborbicular, with a cordate base and doubly serrate margin. Monoecious: male flowers in long pendant yellowish catkins (3-8 cm) that form in autumn and mature in winter; female flowers are tiny with red stigmas barely visible from a bud. Fruit is the hazelnut, enclosed in a toothed leafy involucre.
Habitat and distribution
In Madrid, grows naturally in hedges, forest edges and cool ravines of the northern sierra (above 800 m). Planted as ornamental and fruit-bearing shrub in gardens. Rarer in the drier south and southeast.
Health impact
Very early pollination (January-March), often the first Betulaceae to release pollen. Moderate allergenicity. Cor a 1 is homologous to birch Bet v 1. Hazelnut as food is also an important food allergen (Cor a 8, Cor a 9), potentially causing reactions from oral allergy syndrome to anaphylaxis.
Cross-reactivity
High cross-reactivity with birch and alder through PR-10 protein homology. Hazel-birch syndrome means birch pollen-allergic patients often develop hazelnut food allergy. Also cross-reactivity with rosaceous fruits.
Pollen morphology
Triporate pollen grain, oblate-spheroidal, 22-28 μm. Operculate pores with slight annular thickening. Granular to finely verrucose surface. Exine 1.5-2 μm. Distinguished from birch by slightly more robust appearance and somewhat larger pores.
Did you know?
Hazel flowers during the coldest winter days when most plants are dormant. Its pendant catkins release pollen clouds with the slightest breeze, making it one of the earliest signs of the allergenic season. Hazel rods have been traditionally used as divining rods to find water.
The information on this page is for educational purposes. For any questions about allergies, consult your doctor or allergist.