Black Alder is a familiar species found growing next to watercourses. Trees release clouds of pollen in early spring, and are one of the principal species known to cause allergic rhinitis among sufferers. Also known as Common Alder.

Native to all north-west Europe, extending east through Russia, the Caucasus and northern Iran. Native to Britain and Ireland and found everywhere.

Monoecious. Wind-pollinated. Seeds dispersed by water as the ‘cones’ and seeds both float, remaining viable for a year. A pioneer species adapted to grow in the open, especially wet and compacted soils. A relatively short-lived tree (60–100 years).

A distinctive medium tree (to 28m) of lakes, rivers, ponds, ditches and other wet soils. Usually single-stemmed but often coppiced or machine-cut into multi-stemmed stools, with twisting branches bearing persistent winter 'cones'. Bark dark brown with pale lenticel bands, fissuring into plates. Twigs glabrous, sticky when young, with mauve-tinged stalked buds. Leaves blunt and often notched ('racquet-shaped'), irregularly lobed and serrate. Male catkins 3-10cm; female woody cone-like. Italian Alder differs: glossy pointed leaves, larger cones.

Prefers moist or wet soils but is otherwise very hardy, intolerant of shade and drought-sensitive. It establishes and grows rapidly, and its nitrogen-fixing improves soil and fertilises neighbours, especially demanding broadleaves like Common Walnut. An excellent nurse, it does not persist once neighbours compete. It can be coppiced and is generally tolerant of browsing.

Black Alder is an important species in riparian habitats, forming unique carr woodland (waterlogged and dense thickets), alongside willows and birches. Its roots protect riverbanks, and provide spawning sites for fish. Leaves consumed by many insects, including aquatic species.

Phytophthora alni is a significant pathogen causing dieback or death among alder trees, distributed in water and soil. Climate change may lead to loss of habitat on marginal sites. On drier soils it is prone to drought.

Black Alder is highly valuable for 'ecosystem engineering', conserving fragile sites and creating riparian habitats. Its timber, once valued but now little used, is white when cut but soon oxidises orange-red; relatively soft, it was the wood of choice for clog soles and mouldings. Charcoal from it was once important in gunpowder manufacture, with trees managed on a coppice cycle.