Hazel (Corylus avellana)
Flowering: January - March
Hazel may reach up 2 to 5 meters height. The alternate leaves are suborbicular shaped, irregularly toothed and softly hairy. The smoothed trunk is brownish and becomes greyish over time. The male flowers are grouped in pending yellowish catkins and female flowers are small buds with red styles.
It is widely found in Belgium. It is a shade or intermediate shade tolerant species. It is commonly found in undergrowth, in forest clearing and forest border. It is present on fertile soils, with basic to lowly acidic pH. Various cultured strains have been planted in our parks and gardens.
This is one of the first pollen wave of the year. In this period, there is a confusion between the symptoms of hay fever and those of a common cold.
Cross-reactive allergy: there is cross-reactive allergy between the pollens of the different Betulaceae species (alder, hazel, hornbeam and birch). Therefore, individuals allergic to birch pollen may also experience allergy symptoms at the beginning of the year, when the concentrations of alder and hazel pollens are very high.