Alder (Alnus spp.)

Generar Information

Family: Birch family (Betulaceae)
Flowering period in Central Europe: Winter to early spring
Months: 1–5 (6)

Allergy potential
Moderate to strong allergenicity. Main allergen Aln g1.

Due to the high similarity of the main allergen, cross-reactions with hazel and birch pollen are common (Aln g1 and Bet v1 have a 90% identical protein structure).

Botanical Information

Widely distributed in the Northern Hemisphere, southernmost natural distribution in the Andes of South America. Habitats — Mainly in floodplain and marsh forests, along standing waters, plains to mountainous areas.

Habit — Tree or shrub. Foliage — Summer-green, leaves roundish broad to inversely egg-shaped, leaf margin doubly serrated. Reproduction — Monoecious, ♂ catkins, ♀ catkins mature to woody cones, flowering before leaf emergence.

Common species in Europe

Black or common alder (Alnus glutinosa).
Habit — Tree. Distribution — Common throughout Europe. Floodplain and marsh forests, along rivers, lakeshores, and bogs, on waterlogged soils and slopes. Plains to mountainous areas, up to 1000m altitude. Flowering period in Central Europe — February to April.

Grey or speckled alder (Alnus incana).
Habit — Tree. Distribution — Widespread in northeastern Europe, absent in Western Europe, naturalized in large parts of Central Europe (slope stabilization, reforestation, ornamental shrub). Habitats — Along streams and rivers in mountainous areas, floodplain forests, and moist slopes. In Central Europe at 500–1400m altitude. Flowering period in Central Europe — February to March (slightly earlier than black alder).

Spaeth alder (Alnus x spaehtii, a cultivated hybrid).
Habit - Tree. Habitats — Planted in cities and parks. Flowering period in Central Europe — End of December to beginning of January, responsible for Christmas hay fever.

Green alder (Alnus viridis).
Habit - Shrub. Distribution — In the mountainous regions of the Alps, the Balkans, and the Carpathians from 1600m to the tree line. In the far North part of taiga and tundra. Flowering period in Central Europe — May to June.