Alder (Alnus)

Family:

Birch family (Betulaceae)

Flowering period:

December to June

Distribution:

widespread throughout Europe near to stable water source, even at higher altitudes, namely by green alder (flowering May-June)

Appearance:

summer green, deciduous trees or shrubs, the leaves are obovate to roundish shaped, leaf margin coarsely doubly serrated, female and male catkins are formed, the female catkins become woody

Important species in Europe:

Alnus glutinosa (black or common alder): up to 700m above sea level, especially on moist sites (stream banks, ditches, forest mires).

Alnus viridis (Green Alder): shrub, subalpine to montane (predominantly at timber line) on silicate soils with ample surface water supply, superseding Pinus mugo (which grows at similar elevations on limestone)

Alnus incana (grey or speckled alder): widespread, but absent in Western Europe, used for reforestation and stabilization of slopes and embankments, blooms February to March - usually a bit earlier than black alder.

Alnus x spaethii: the product of a hybridisation, the source of pollen up to two months before other alder species in European cities where it is planted (for example, Christmas hay fever in parts of Switzerland)

Allergenicity:

moderate to high allergenicity, frequent cross-reaction to pollen from hazel and birch (major allergen Aln g1 >90% identical with Bet v1)

Link zum Pollenatlas: Alnus glutinosa