Read about Hydrangea quercifolia – Oakleaf hydrangea
Hydrangea sp., common names hydrangea or hortensia, is a genus of 70–75 species of flowering plants native to southern and eastern Asia [China, Japan, Korea, the Himalayas and Indonesia] and the Americas. By far the greatest species diversity is in eastern Asia, notably China, Japan, and Korea. Most are shrubs 1 to 3 meters tall, but some are small trees, and others lianas reaching up to 30 m [98 ft] 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 in some species [notably Hydragea macrophylla], can be blue, red, pink, light purple, or dark purple. In these species the color is affected by soil pH.
For Hydrangea macrophylla and Hydrangea serrata cultivars, the flower color can be determined by the relative acidity of the soil: an acidic soil [pH below 7], by the influence of sundry agents in the soil, such as alum or iron, will usually produce flower color closer to blue, whereas an alkaline soil [pH above 7] will produce pinker flowers. This is caused by a color change of the flower pigments in the presence of aluminium ions which can be taken up into hyperaccumulating plants.