Alnus glutinosa
Betulaceae
February to April
It is found throughout the country.
See the BSBI distribution map for Alder
It grows on damp or wet soils - beside rivers, streams,
canals, lakes and ditches, and areas prone to seasonal
flooding.
It has a requirement for water in the early stages of
growth.
It is a pioneer plant - growing on bare areas and paving
the way for other plants to follow.
Nodules on the roots contain an actinomycete, Frankia,
which fixes nitrogen and enables alder to colonise
nitrogen-poor soils.
Alder is a native, deciduous tree growing to 22m, but
often much shorter.
Male catkins are yellowish and dangling, up to 5cm
and at the end of twigs..
Female flowers are also at the end of twigs, up to 1cm
and with 2 red linear styles per bract*.
Cones turn from green to black and persist.
Leaves are dark green, strongly veined, up to 9cm,
broadly ovate and with short petioles.
* ScienceDaily, 13 February 2025.
.It has been shown that the red stigmas in wind-pollinated
trees accumulate anthocyanin, the same compounds that
are revealed in autumn leaves after green chlorophyll
production slows down. The anthocyanin supports pollen
germination and growth by acting as an antioxidant.
Wei-Hao Wang et al.(2025) Molecular Biology and
Evolution, DOI: 10.1093/molbev/msaf040
.Genetic mechanisms and adaptive benefits of
anthocyanin-red stigmas in a wind-pollinated tree.
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Alder tree with catkins
Female flowers
Close-up of female flowers. 2 styles
per bract
Male flowers - catkins
Close-up of male flowers with 4 stamens
per bract
Alder leaf
Cone in summer
Â
Old cone persisting on tree
Male and female flowers in January
Alder invading wet land
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