Wood character traits of Alnus (Betulaceae) trees and shrubs

Summary Alnus is a nitrogen-fixing genus of woody plants, widely distributed across temperate regions of the Northern Hemisphere, with several species extending into subtropical and montane tropical zones, including the neotropics. Species vary in growth habit, ranging from tall trees to dwarf trees or multi-stemmed shrubs, and some display flexibility between these forms. In other woody lineages, such differences in growth habit have been linked to variation in wood anatomical traits, but this relationship has not been systematically evaluated in Alnus . Here, we examined 24 species of Alnus , including 11 tree species, 7 shrub species and 6 species exhibiting both habits, for wood anatomical characters following the IAWA Hardwood List. None of the evaluated anatomical traits was found to be predominant in either tree or shrub growth habits. In fact, Alnus demonstrated little inter-species anatomical variability. Nevertheless, this dataset provides the first comparative overview of Alnus wood anatomy across growth forms and offers a foundation for future studies that incorporate broader ecological and geographic sampling in the genus Alnus and beyond.