Alnus incana Monstrosa - Grey Alder

Alnus incana 'Monstrosa' is an unusual, rare form of the white alder. It could have been called the 'Monstrous' alder, as the plant exhibits a deformity called fasciation, quite common in the plant kingdom. This is a mutation that is responsible for its small size and the very unusual appearance of its branches. Its foliage resembles that of the classic white alder, but smaller, and it grows on frond-like branches that are carried by short branches, flattened at their ends, grooved and more or less twisted. This dwarf tree with its picturesque structure is especially interesting in winter when it is devoid of leaves.

Alnus incana 'Monstrosa' was discovered in Poland around 1883 and introduced into cultivation by the German nursery Späth. It is a deciduous tree of the Betulaceae family, just like birches. The species, also known as the mountain alder or grey alder, is native to temperate regions of the northern hemisphere and is hardy down to -36ºC. Thanks to its flexibility and ability to produce shoots, it is one of the few trees capable of withstanding avalanches. It is a pioneer species, fast-growing, capable of forming dense stands in poor, limestone soil. Its deep and running root system allows it to withstand wind and anchor itself firmly even in very unstable, sloping soil. The white alder likes limestone soils and adapts well to both wet and fairly dry soils in summer.

The white alder 'Monstrosa' slowly forms a large, rounded, and bushy shrub, with spreading branches, measuring about 2 m in all directions. This variety develops a very short trunk that gives rise to a dense crown. The branches have a characteristic pinnate structure. The trunk, as well as the young branches, are a somewhat greyish brown. The deciduous foliage appears in spring and falls in autumn. It is very dense, dark green, composed of elongated, strongly toothed leaves. The undersides of the leaves are covered with a light down. The leaves are a fairly dark green, slightly glossy. They fall in autumn. The fasciation, of uncertain origin, is the result of abnormal growth at the apex of a stem. Fasciation is manifested by flattened, striated stems in a bundle-like form.

Alnus incana 'Monstrosa' should be placed prominently, as a specimen plant, so that it can be admired in winter. It will be highlighted by a water feature. It can also be integrated into an exotic-inspired bed, amidst male ferns, for example. In a different style, plant violets (Viola) or periwinkles at its base. It can also be grown in a large container on the terrace. Being very hardy, it likes rich, limestone soils. Plant collectors will also appreciate Aesculus hippocastanum 'Monstrosa', Salix erythroflexuosa willow, and Robinia pseudoacacia 'Twisty Baby' black locust.

The white alder is often planted to colonise poor and unstable soils in the mountains, as well as on slag heaps. Its root system forms nodules containing bacteria that fix nitrogen from the air, returning this richness to the soil. It is also found in windbreak hedges in the plains. It is a very robust tree that tolerates water shortage once well-rooted.

Alnus incana comes from the Latin word incanus, which means "covered with greyish-white hairs," referring to the hairy undersides of the young leaves. The leaf is used as a diuretic and vermifuge. The bark is astringent and tonic.