Hydrangea is a genus of about 70–75 species of flowering plants native to southern and eastern Asia and North and South America. Most are shrubs 1–3 m tall, but some are small trees, and others lianas reaching up to 30 m by climbing up trees. They can be either deciduous or evergreen, though the widely cultivated temperate species are all deciduous.
In most species the flowers are white, but others (notably H. macrophylla), can be blue, red, pink, light purple, or dark purple. Hydrangea flowers are produced from early spring to late fall; they grow in flowerheads (corymbs or panicles) at the ends of the stems.
There are two flower arrangements in hydrangeas. Mophead flowers are large round flowerheads resembling pom-poms or, as the name implies, the head of a mop. In contrast, lacecap flowers bear round, flat flowerheads with a center core of subdued, fertile flowers surrounded by outer rings of showy, sterile flowers.