Latin name: Alnus spp.
Plant description: Medium sized tree with oval, serrated leaves, the tip indented on some species. Dense, wine-red catkins produce the pollen. Fruit: small cones, green at first, then brown.
Distribution: UK: countrywide. Also across much of Europe, Western Asia, North-Western USA and North Africa, growing in or near watercourses.
Allergenicity and other health impacts: Alder pollen has moderate to high allergenicity. It can cross-react with birch pollen so some birch-pollen sufferers may be affected by alder pollen. There are only two allergenic pollen types that occur in the late winter, hazel and alder, so if you have symptoms at that time then one or both of these may be the culprit.
Season: Mid-January to mid-April, usually peaking in February but the peak can be delayed if the Winter weather is severe.