Sources:
http://nativeplantspnw.com/red-alder-alnus-rubra/
http://www.tree-guide.com/european-alder
https://www.paganpens.co.uk/the-oghma-calendar
http://www.ecoenchantments.co.uk/myogham_alderpage.html
https://www.celticjewelry.com/celtic-culture/alder-april
https://plants.usda.gov/plantguide/pdf/cs_alru2.pdf