Spiraea japonica is a dense, upright, mounded, deciduous shrub that typically grows 4-6' tall with a slightly larger spread. Leaves are oval and sharply-toothed. Tiny pink flowers in flat-topped clusters.
A common habitat for Spiraea japonica in general seems to be in riparian areas, bogs, or other wetland habitats. It is found growing along streams, rivers, forest edges, roadsides, successional fields, and power line right-of-ways. It prefers lots of water during the growing season; however, it cannot tolerate saturated soils for extended periods of time.
It is naturally variable in form and there are many varieties of it in the horticulture trade.