Hydrangea (Hydrangea macrophylla) is a flowering shrub. It is native to Japan, from where it was imported to Europe as an ornamental plant in the 18th century. Noble hydrangea has large, dark toothed leaves that grow opposite each other on the branches. The flowers form dense spherical clusters. Many different varieties of noble hydrangea have been bred. Most flowers are pH sensitive: if a plant grows in acidic soil, its flowers are blue or purple, but in alkaline soil they become red.