Alder, Alnus

tree of the family Betulaceae (Alder, Birch, Hornbeam)

Etymology: "alder" comes from the radical " al ", ancient appellation in France was " verne ", hence Verneuil; in Breton: "guern", hence the prefix " Guer ".
Origin: Southern Europe.
European species: Alder, Alnus glutinosa (because of the viscosity of its buds and its young leaves); alder of Corsican (native to Corsican) or Alder with cordate leaves, Alnus cordata; whitish Alder, Alnus incana.
Other species: Red Alder, Alnus rubra and Alnus viridis of North America, Alnus sieboldiana of Japan.
Habitat : species of light, alders appreciate the sunny fields. The Alder and the Alder of Corsican grow in wetlands. The whitish alder adapts to dry and calcareous soils (limestones are often dry because they let the water circulate). It supports altitude. It is possible to meet Alders a bit everywhere in France, and in all Europe, but seldom in Mediterranean region.
Alders sucker from roots and this feature is used to plant them in dense and pruned hedge. Their roots enrich the poor soils in nitrates thanks to a symbiosis with a procaryote of the genus Frankia fixing the nitrogen of air (Fabaceae also fixes the nitrogen). That is why the alder is a plant actinorhizae (that is of actinomyceteses in form of mycorrhiza). Undemanding, the Alder colonizes waste lands and rubble and prepares the ground for more demanding species. One says that the Alder is a pioneer species (as the filao, under tropical climates).
Hardiness: zone 7 (it supports cold until -17 °C or 1° F).
Form (insulated tree): conical on broad base, due to its branches which grow to the horizontal. Its foliage is sparse.

Height: 30 m tall. Slow growth. Alone, the alder of Corsican has a quick growth.

Blackish grey bark which cracks by flakes (common alder); smooth, grey, interspersed with lenticels and with short vertical crack (alder of Corsican). The trunk of the alder bleeds when it is cracked.

alder of old Corsican

alder of young Corsican
Deciduous foliage (leaves remain green late in autumn). Leaves alternate. Purple buds in winter which hatch in February.
Flowers: the male flowers are catkins pendulous, turn purple and long, which can cast their pollen in the wind while the female flowers are smaller. Blossoming takes place in February. It is one of the first blossoming anemophilous of the year.
Fruit : the fruit is a small alder cones dark brown, the strobilus, 2cm in length. It contains small achenes winged wind-dispersed. It remains on the tree all year.
Risk of allergenic pollen : high.
Difference Whitish alder Alder Alder of Corsican
Size 10-15 m 20-30 m 25 m
Lifespan 100 years 150 years 100 years
Leaves lanceolate, less than 15 veins round, heart-shaped tip at the petiole, dentate Heart-shaped tip at the apex
Petiole   court  
Base in V in V heart-shaped

Legends and traditions: In Greek mythology, tree of Dead (God Cronos).
Due to its habitat in marshes and to red colour blood of its cracked wood, the Alder was linked to the sorceresses. Power was allocated to move away the fire of hous or the rodents of fields, and to facilitate the birthing of livestock.
Uses: the Alder is used to reafforest lands uncultivated. The Alder (as the willow) is efficient in the maintaining of banks thanks to its deep root system.
Its wood is light and soft, but it tends to split. Once cut, it turns red in the air, which earned her superstitions. It is said that "bleed". Add to that alder was used to build the gallows! Goethe took up this belief in Le roi des Aulnes, a poem set to music by Schubert.
The alder is deemed to rot and harden on contact with water. The piles in Venice are made of Alder (Elms also) and hooves too. Of the bark and twigs, were extracted from the black dye markers. The bark contains principles febrifuge. The Indians dug the trunk of the American variety to make canoes.

Other species:

  • Alnus glutinosa "Imperialis", Alder laciniate.
    As other alders, it produces catkins at the end of summer which mature next summer in similar cones (strobiles).

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