Hydrangea

Hydrangea is a genus of over 70 flowering plant species that are native to Asia and the Americas. The genus was first described from Virginia in North America, but the highest concentration of species is found in eastern Asia, especially China, Korea, and Japan. Most hydrangeas are shrubs that grow 1 to 3 meters tall, though some are small trees, and others are climbing lianas that can reach up to 30 meters. They can be deciduous or evergreen, but the commonly cultivated temperate species are all deciduous.

The name *Hydrangea* comes from Greek, meaning "water vessel," referring to the shape of the seed capsules. The earlier name *Hortensia* is a Latinized version of the French given name Hortense. Philibert Commerson had tried to name the flower *Lepautia* or *Peautia* after astronomer Nicole-Reine Lepaute, but the common name became *Hortensia*, which led to the mistaken belief that Lepaute's name was Hortense. The Larousse dictionary notes this is incorrect, and the name likely came from *hortus*, meaning garden.

Hydrangeas bloom from early spring to late autumn, producing flowerheads called corymbs or panicles, usually at the ends of stems. These flowerheads typically contain two types of flowers: small, non-showy fertile flowers in the center, and large, sterile showy flowers with colorful sepals around the outside. Wild populations often have few or none of the showy flowers, while cultivated varieties have been bred to have more of the larger type. There are two main flower arrangements in corymb-style hydrangeas: mophead flowers, which are large and round like pom-poms, and lacecap flowers, which are flat with a center of small flowers surrounded by rings of larger ones. Some rhododendrons and viburnums can look similar to hydrangeas at first glance.

Hydrangea flower color can change based on soil pH. Soil with a pH of 5.5 or lower produces blue flowers, a pH of 6.5 or higher produces pink flowers, and soil between 5.5 and 6.5 yields purple flowers. White hydrangeas cannot change color through soil pH because they lack the pigment. In most species, flowers are white, but in some, especially *Hydrangea macrophylla*, they can be blue, red, or purple, with color saturation genetically predetermined. The color change occurs due to the availability of aluminum ions, which depends on soil pH: acidic soil makes aluminum available, leading to blue or purple flowers, while alkaline soil binds aluminum, resulting in pink or red flowers.

There are 98 accepted species of hydrangea. Fossil records include *Hydrangea alaskana* from Paleogene strata in Alaska, *Hydrangea knowltoni* from Miocene deposits in the Pacific Northwest, *Hydrangea bendirei* from Oregon, *Hydrangea reticulata* from California, and *Hydrangea polonica* from Miocene freshwater deposits in Poland.

Hydrangeas are popular ornamental plants, especially *Hydrangea macrophylla*, which has over 600 named cultivars, many bred to have only large sterile flowers. This species is divided into mophead and lacecap types. Some hydrangeas need annual pruning when new leaf buds appear; otherwise, they become leggy and may sag or break. Other species flower only on old wood, so pruning new wood will delay flowering until the next season. Certain cultivars and species have received the Royal Horticultural Society's Award of Garden Merit under the synonym *Schizophragma*, including *S. hydrangeoides* var. *concolor* 'Moonlight', *S. hydrangeoides* var. *hydrangeoides* 'Roseum', and *S. integrifolium*. Hydrangea root and rhizome are used in herbal medicine for urinary tract conditions and may have diuretic properties, but all parts of the plant are moderately toxic if eaten.