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Hydrangea

See text Hydrangea (/haɪˈdreɪndʒiə/; common names hydrangea or hortensia) is a genus of 70–75 species of flowering plants native to southern and eastern Asia (China, Japan, Taiwan, 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.

Hydrangea (/haɪˈdreɪndʒiə/;[1] common names hydrangea or hortensia) is a genus of 70–75 species of flowering plantsnative to southern and eastern Asia (China, Japan, Taiwan, 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 30m (98ft) by climbing up trees. They can be either deciduous or evergreen, though the widely cultivated temperate species are all deciduous.[2]

Having been introduced to the Azores, H. macrophylla is now very common, particularly on Faial, which is known as the "blue island" due to the vast number of hydrangeas present on the island.

‘Hydrangea’ is derived from Greek and means ‘water vessel’, which is in reference to the shape of its seed capsules.[3] The earlier name, Hortensia, is a Latinised version of the French given name Hortense, referring to the wife of Jean-André Lepaute.[4]

Life cycle

Hydrangeaflowers are produced from early spring to late autumn; they grow in flowerheads (corymbs or panicles) most often at the ends of the stems. Typically the flowerheads contain two types of flowers: small non-showy flowers in the center or interior of the flowerhead, and large, showy flowers with large colorful sepals (tepals). These showy flowers are often extended in a ring, or to the exterior of the small flowers. Plants in wild populations typically have few to none of the showy flowers, while cultivated hydrangeas have been bred and selected to have more of the larger type flowers.

There are two flower arrangements in hydrangeas with corymb style inflorescences, which includes the commonly grown "bigleaf hydrangea"—Hydrangea macrophylla. 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, small flowers surrounded by outer rings of larger flowers having showy sepals or tepals. The flowers of some rhododendrons and viburnums can appear, at first glance, similar to those of some hydrangeas.

Colours and soil acidity

Hydrangea flower color changes based on the pH in soil. As the graph depicts, soil with a pH of 5.5 or lower will sprout blue hydrangeas, a ph of 6.5 or higher will produce pink hydrangeas, and soil in between 5.5 and 6.5 will have purple hydrangeas. White hydrangeas can not be manipulated by soil pH, they will always be white because they do not contain pigment for color.

In most species the flowers are white, but in some species (notably H. macrophylla), can be blue, red, pink, light purple, or dark purple. In these species the color is affected by the presence of aluminium ions which are available or tied up depending upon the soil pH.[5][6] For H. macrophylla and H. serrata cultivars, the flower color can be determined by the relative acidity of the soil: an acidic soil (pH below 7), will have available aluminum ions and typically produce flowers that are blue to purple,[7] whereas an alkaline soil (pH above 7) will tie up aluminum ions and result in pink or red 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.[8] Lowering the pH of potting soils or mixes usually does not change the flower color to blue, because these soils have no aluminum ions. The ability to blue or pink a hydrangea is also influenced by the cultivar. Some plants are selected for their ability to be blued, while others are bred and selected to be red, pink or white. The flower color of most other Hydrangea species is not affected by aluminum and cannot be changed or shifted. Hydrangeas also have a nickname called 'Change Rose'.

Cultivation and uses

Hydrangeas are popular ornamental plants, grown for their large flowerheads, with Hydrangea macrophylla being by far the most widely grown with over 600 named cultivars, many selected to have only large sterile flowers in the flowerheads. Hydrangea macrophylla, also known as Bigleaf Hydrangea, can be broken up into two main categories; Mophead Hydrangea & Lacecap Hydrangea.[10] Some are best pruned on an annual basis when the new leaf buds begin to appear. If not pruned regularly, the bush will become very 'leggy', growing upwards until the weight of the stems is greater than their strength, at which point the stems will sag down to the ground and possibly break. Other species only flower on 'old wood'. Thus new wood resulting from pruning will not produce flowers until the following season.

Hydrangea root and rhizome are indicated for treatment of conditions of the urinary tract in the PDR for Herbal Medicine and may have diuretic properties.[11] Hydrangeas are moderately toxic if eaten, with all parts of the plant containing cyanogenic glycosides.[12]Hydrangea paniculata is reportedly sometimes smoked as an intoxicant, despite the danger of illness and/or death due to the cyanide.[13][14]

The flowers on a hydrangea shrub can change from blue to pink or from pink to blue from one season to the next depending on the acidity level of the soil.[15] Adding organic materials such as coffee grounds, citrus peel or eggshells will increase acidity and turn hydrangea flowers pink, as described in an article on Gardenista.[16]
A popular pink hydrangea called Vanilla Strawberry has been named "Top Plant" by the American Nursery and Landscape Association.

The hybrid "Runaway Bride Snow White", bred by Ushio Sakazaki from Japan, was named Plant of the Year at the 2018 RHS Chelsea Flower Show.[17]

In culture

In Japan, ama-cha,甘茶 meaning sweet tea, is another herbal tea made from Hydrangea serrata, whose leaves contain a substance that develops a sweet taste (phyllodulcin). For the fullest taste, fresh leaves are crumpled, steamed, and dried, yielding dark brown tea leaves. Ama-cha is mainly used for kan-butsu-e (the Buddha bathing ceremony) on April 8 every year—the day thought to be Buddha's birthday in Japan. During the ceremony, Ama-cha is poured over a statue of Buddha and served to people in attendance. A legend has it that on the day Buddha was born, nine dragons poured Amrita over him; ama-cha is substituted for Amrita in Japan.

The pink hydrangea has risen in popularity all over the world, but especially in Asia. Pink hydrangeas have many different meanings, but generally mean, "You are the beat of my heart," as described by the celebrated Asian florist Tan Jun Yong, where he was quoted saying, "The light delicate blush of the petals reminds me of a beating heart, while the size could only match the heart of the sender!"[18]

Hydrangea quercifolia was declared the official state wildflower of Alabama in 1999.[19]