The Alder genus (Alnus).
Finding out what Alder species you are dealing with.
See also hereIn the Netherlands three species are seen: - Common alder; European alder; Black alder or Alnus glutinosa grows 35 meters tall. The leaf has 5-8 veins. Bark first smooth grey-brown, later dark-grey to black-brown with grooves. This is the most common Dutch Alder which you can see about everywhere near water.
- The Speckled alder. or Alnus incana is much less common and often only very small. Can become 25 meters. The leaf has 8-14 veins. Bark is grey or yellowish-smooth with almost no clear rough bark. Leaf is a little bit more pointy than the Common alder. I have no pics of this species yet.
The two species above can cross-fertilize and form individuals wit characteristics of both.
- Italian alder or Alnus cordata. Has an evenly serrated edges and is heart-shaped. Female catlins in bunches of 1-3 against bunches of 3-5 for the two species above.
The following alder is probably Alnus x spaethii. See also this article in Dutch. Alnus x spaethii is a hybrid between A. japonica (Japanese alder) and A. subcordata (Caucasian alder).
The parent characteristics are easily recognized: . ’Spaeth’ grows on dry places like the Japanese alder. Also its leafs are like A. japonica, but they are bigger and when they are just out of the bud they are redish-brown. The last character is from A. subcordata. ’Spaeth’ has small hairs on the underside of the leaf, same as subcordata. ’Spaeth’ can stand the Dutch climate betetr than the Japanese Alder and can even stand sea-wind. You find individuals throughout Dukenburg in Nijmegen.
Alders are related closely to Birches and also the Filberts like European filbert and the Hornbeam.
All species photographed.
Alnus speathii
Speckled Alder 
Leafs of the species photographed.
Winter photo's of bark and buds, if available.
Here you see two species: The Cmmon alder and Alnus Spaethii. The black alder has grey round buds, and the spaethii smaller green ones.
