Hydrangea ( or ) is a genus of more than 70 species of flowering plants native to Asia and the Americas. Hydrangea is also used as the common name for the genus; some (particularly H. macrophylla) are also often called hortensia. The genus was first described from Virginia in North America, but by far the greatest species diversity is in eastern Asia, notably China, Korea, and Japan. Most are shrubs 1–3 m (3 ft 3 in – 9 ft 10 in) tall, but some are small trees, and others lianas reaching up to 30 m (100 ft) by climbing up trees. They can be either deciduous or evergreen, though the widely cultivated temperate species are all deciduous.

The flowers of many hydrangeas act as natural pH indicators, producing blue flowers when the soil is acidic and pink ones when the soil is alkaline.

...