Species list


Alnus glutinosa

Common alder

Common alder, black alder, European alder, alder (Eng), aliso, humero (Spa), vern (Cat), altza (Baq), ameneiro (Glg), amieiro-vulgar (Por).


“It is not flat at all, it is somewhat convex, it sinks mysteriously down, towards the alders, to kiss the brook”.

‘Doña Berta’, Leopoldo Alas, 'Clarín'


The common alder is a slender tree with grey, flaky bark that grows up to 25 m tall. It often has a conical crown, like a conifer. The novelist 'Clarín' reminds us of it again in Doña Berta: “At the northwestern end of the pasture flows a stream fringed by tall poplars, birches and dark-leaved, conical alders...”. The leaves are 4-14 cm long, deciduous, simple, alternate, rounded, oblong and even heart-shaped. They have a sinuate, slightly irregular contour and a finely serrated or toothed margin. The tip is usually notched and not pointed. The male flowers are arranged on long hanging peduncules called catkins, which contain the pollen. And this is not the only way they resemble conifers, as when ripe the female flowers form structures resembling small cones, which contain the seeds.


This species is associated with watercourses, forming gallery forests (alisedas), and is found with willows, poplars, elms and ash trees. It can stand hard pruning, but suffers a lot if the watercourses run dry, especially if its roots are left in the air, even if the water table is at the surface. It tends to be happiest in mid-mountain areas, being found in copses, valley bottoms with permanent water, and areas with developed and fairly deep soils. It is only found at altitudes of up to around 1700 m. Although it is indifferent to substrate, it does best on lime-free soils. In addition, its roots have nodules that house a symbiotic nitrogen-fixing fungus, so this plant fertilises the soil that it grows on.


This tree lives throughout most of Europe, Asia, and northwestern Africa. It is a common species on the Iberian Peninsula but it is most abundant in the west. It is scarce or disappears completely in drier regions, towards the east and southeast, and it is not found in the Balearic Islands.