Definition of "spp."

Fagus sylvatica (European beech) and Acer saccharum (sugar maple, from North America) are very tolerant of deep shade, while Betula spp. (birches) and Populus spp. (poplars) grow best under high light intensities.

2011, Peter A. Thomas, “General Forest Ecological Processes: Chapter 10 from Trees and Forests, a Color Guide”, in Arnoldia, volume 68, number 3 (in English), Boston, MA: Arnold Arboretum of Harvard University, page 22