There are about 80 species of the genus Spiraea throughout the world. Spireas are important ornamental shrubs. Most of the important ornamentals have been introduced from China and Japan. A common habitat for the genus in general seems to be in riparian areas, bogs, or other wetland habitats. However, the eastern and western forms of birchleaf spirea occur on drier upland sites than do other species. They seem to achieve their greatest stature and best growth following disturbances such as fire or flooding that remove the overtopping trees and thus make light and other resources more available. Native spireas are generally 1 to 2 m tall. Plants growing at higher elevations tend to be shorter in stature than those at low elevations. Individual plant form tends to be a multi-stemmed clump arising from basal sprouting. Many species are rhizomatous and capable of forming dense stands. Individual flowers are very small (1.5 mm) and perfect. They are borne in terminal clusters of various sizes shapes and colors (white and pink deep rose). Seeds are borne in a follicle and measure 2 to 3 mm in length. Dispersal begins when the fruit becomes straw-colored or light brown and splits down one side.
Guide to Identify Presented Species of Genus Spiraea
FLOWERS WHITE
S. betulifolia – White Spiraea Spreading shrub, about 25-60 cm tall. Moist to dry mountain slopes.
Flowers white, many in clusters 3-8 cm broad. The 5 petals 2 mm long.
Leaves alternate, oval, about 2-7 cm long, coarsely sharp-toothed.
