Britain's native alder is the rather sticky-leaved Alnus glutinosa. It is widespread in our county, growing beside rivers and streams and is also frequent in wet woodlands, where it produces its catkins from February through to early April. Its seeds are interesting because they contain air-tight cavities and these, together with an oil protecting them from wet, allow them to float unharmed throughout the winter to germinate on mud or damp soil in the spring.
The Italian Alder, Alnus cordata, is widely planted both as a street tree and in gardens and in urban areas it is perhaps the commonest alder. Its flowering times are similar to those of our native alder but the species is rarely self-sown. Perhaps our climate is too far removed from its home in southern Italy and Corsica.
The third species likely to be encountered is the exceptionally hardy Grey Alder, Alnus incana. I have certainly seen it growing beside streams in, for example, Byfield, but its habit of suckering makes it a potential nuisance in gardens. However, it flowers early with its catkins appearing in January or even December, so when I saw an alder in Daventry today I immediately suspected, as it bore hundreds of catkins, that it was this species. But...
|Alder catkins. Daventry, 24 January, 2017|
|Last year's female 'cones, now dry and hard. Daventry, 24 January, 2017|