There are about 30 species of Alnus.
They include both shrubs and trees that are
native to the cool temperate zones with a
few from as far south as
Central America.
The
term, "alder" probably comes from the Old
English word, alor, or the Old High
German words, elo or elawer which
mean reddish-yellow. This refers to the color
developed by freshly cut wood from trees of this
genus.