There are several species, the best known being the American alnifolia, 3-4 ft., with Alder-like leaves and racemes of white flowers from July to September, and arborea, from Madeira, 8-10 ft. high; acuminata, 10-15 ft.; paniculata, scabra, and tomentosa, all from North America, and 3-4 ft. high; all have white flowers. To these may be added canescens, from China and Japan, which has racemes of white Hawthorn-like flowers in July.