Grey alder

Aulne gris

Alnus incana (L.) Moench ssp. incanaBetulaceae (birch family)

Origin: Europe and Asia


Grey alder is a medium-sized tree with a cone-shaped crown.

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Leaves are broadly oval, with doubly toothed edges and hairy stalks.

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Flowers are tiny, clustered in separate male and female catkins.

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Fruits are nutlets borne in brown, woody, conelike catkins

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Grey alder is a medium-sized tree, up to 21 m (70') tall.

The crown is cone shaped.

Bark is smooth and grey with horizontal pores (lenticels).

Bark becomes rough with age.

Twigs are greyish-brown and hairy. Buds are downy, 6 - 12 mm (1/4" - 1/2") long, borne on short stalks.

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Leaves are 5 - 10 cm (2" - 4") long, broadly oval, with a wedge-shaped or rounded base and a pointed tip.

Leaf edges are doubly toothed with 9 - 12 pairs of impressed veins that terminate in a tooth.

Leaf undersides are whitish grey, often hairy. Leaf stalks are hairy.

Leaves are arranged alternately on the branch.

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Flowers tiny, clustered in separate male catkins and cone-like female catkins on the same tree. Flowers open in early spring, before the leaves.

Mature male catkins are purplish-red, up to 10 cm (4") long, borne in groups of 3 to 4.

Female catkins are short, reddish-purple, cone-like, in groups of 3 - 8.

Young green male catkins develop in midsummer, overwinter on the tree, and mature to shed pollen the following spring.

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Fruits are nutlets borne in cone-like catkins (alder cones) that are green and closed while maturing.

Mature alder cones are brown, woody, 13 - 16 mm (1/2" - 5/8") long, their scales opening to release the winged nutlets in late fall.

Empty alder cones remain on the tree through the winter and can be seen with the new green cones the following summer.

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Distribution and related species

Grey alder, one of several subspecies of Alnus incana, is native to Europe and western Asia. Grey alder and its cultivated varieties (cultivars) are medium-sized trees that are frequently planted in Europe, less so in North America. Another subspecies, speckled alder, is native to northeastern North Amercia. It is a tall shrub or at most a small tree of wetland habitats. These two subspecies can be distinguished from European black alder, Alnus glutinosa, by their leaf tips. Black alder never has pointed tips while speckled and grey alder usually do.

Derivation of names

The genus name Alnus is the classical Latin name for alder. The species name incana is from the Latin for pale grey, a reference to the pale grey bark and undersides of the leaves.

Commercial use

Many species of alder are planted to improve soil quality because they have nitrogen-fixing bacteria on their roots. The fallen leaves of alders also help to fix nitrogen into the soil.

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Grey alder IN TORONTO

Grey alder's place in Toronto's urban forest

Grey alder is occasionally planted in Toronto's parks and cemeteries. In winter, alders are good places to observe winter birds which pick the seeds from the alder cones.

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WHERE CAN I SEE Grey alder?

Find trees on Tree Tour maps at Canadian Tree Tours:

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