Alder: Alnus glutinosa
- Photographs of this tree, its leaves, catkins and cones.
- http://www.plant-identification.co.uk/skye/betulaceae/alnus-glutinosa.htm

Alnus glutinosa (European Alder)
- Images, plant synonyms, and scientific classification. Includes invasive plant and introduced plant information for this species.
- http://plants.usda.gov/java/profile?symbol=ALGL2

Alnus glutinosa (Black Alder)
- Facts on physical characteristics, habitat, range, and ethnobotany. Includes distribution map.
- http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=233500032

Alnus glutinosa (European Black Alder)
- Physical characteristics of leaf, flower, fruit, twig, and bark. Provides images.
- http://www.cnr.vt.edu/dendro/dendrology/syllabus/aglutinosa.htm

Alnus glutinosa
- Short description and medicinal uses.
- http://www.botanical.com/botanical/mgmh/a/alder019.html