Alnus cordata (Italian alder) is a medium-sized tree growing up to 25 m tall (exceptionally to 28 m), with a trunk up to 70–100 cm diameter. The leaves are deciduous but with a very long season in leaf.
The slender cylindrical male catkins are pendulous, reddish and up to 10 cm long; pollination is in early spring, before the leaves emerge. The female catkins are ovoid, when mature in autumn 2–3 cm long and 1.5–2 cm broad, dark green to brown, hard, woody, and superficially similar to some conifer cones. The small winged seeds disperse through the winter, leaving the old woody, blackish ‘cones’ on the tree for up to a year after.