Hydrangea

Hydrangea (/haɪˈdreɪndʒiə/)[1] common names hydrangea or hortensia, is a genus of 70–75 species of flowering plants native to Asia and the Americas. By far the greatest species diversity is in eastern Asia, notably Korea, China, and Japan. 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.[2]

Several terms redirect here. For other uses, see Hydrangea (disambiguation) and Hortensia (disambiguation).

Hydrangea
Hydrangea macrophylla
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Cornales
Family: Hydrangeaceae
Genus: Hydrangea
L.
Species

See text

Hydrangea is derived from Greek and means ‘water vessel’, 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 French astronomer and mathematician Nicole-Reine Lepaute.[4]

Life cycle

Hydrangea flowers 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.

Hydrangea flowers, when cut, dehydrate easily and wilt very fast due to the large surface area of the petals. A wilted hydrangea may have its hydration restored by first having its stem immersed in boiling water; as the petals of the hydrangea can also absorb water, the petals may then be immersed, in room-temperature water, to restore the flower's hydration.[5]

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 cannot 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, floral color change occurs due to the presence of aluminum ions which are available or tied up depending upon the soil pH.[6][7] 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,[8] 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 aluminum ions which can be taken up into hyperaccumulating plants.[9] 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 are also nicknamed 'Change Rose'.

Partial list of species
Hydrangea paniculata

Fossil record

†Hydrangea alaskana is a fossil species recovered from paleogene strata in Jaw Mountain Alaska.[10]

Four fossil seeds of †Hydrangea polonica have been extracted from borehole samples of the Middle Miocene fresh water deposits in Nowy Sacz Basin, West Carpathians, Poland.[11]

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.[12] 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 Physicians' Desk Reference for Herbal Medicine and may have diuretic properties.[13] Hydrangeas are moderately toxic if eaten, with all parts of the plant containing cyanogenic glycosides.[14] Hydrangea paniculata is reportedly sometimes smoked as an intoxicant, despite the danger of illness and/or death due to the cyanide.[15][16]

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.[17] Adding organic materials such as coffee grounds, citrus peel or eggshells will increase acidity and turn hydrangea flowers blue, as described in an article on Gardenista.[18] 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.[19]

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.

In Korean tea, Hydrangea serrata (hangul:산수국 hanja:山水菊) is used for an herbal tea called sugukcha (수국차) or isulcha (이슬차).

The pink hydrangea has risen in popularity all over the world, especially in Asia. The given meaning of pink hydrangeas is popularly tied to the phrase, "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!"[20]

Hydrangea quercifolia was declared the official state wildflower of Alabama in 1999.[21]

Bee-friendliness

Hydrangea variants vary in bee-friendliness and their ability to feed pollinators. In general, the common Hydrangea variants are not bee-friendly because their flowers are sterile, e.g. Hydrangea macrophylla hortensis (mophead) and H. paniculata (limelight). Variants that give food for bees and pollinators are:

  • Hydrangea anomala petiolaris
  • Hydrangea arborescens
  • Hydrangea aspera
  • Hydrangea mycrophylla
  • Hydrangea paniculata (grandiflora)
  • Hydrangea quercifolia
  • Hydrangea macrophylla
  • Hydrangea flowers close up.
  • Flowers
  • Hydrangea macrophylla, flowers.
  • Hydrangea macrophylla, flowers
  • Hydrangea sp painted by the botanical artist Redouté.
  • Hydrangea quercifolia
  • Hydrangea macrophylla, leaves
  • Wild Hydrangea v. Annabelle
    Hydrangea arborescens
  • Wild Hydrangea v. Annabelle
    Hydrangea arborescens
  • 8" Annabelle Hydrangea Bloom. Hydrangea arborescens.
  • Hydrangea aspera ssp. sargentiana
  • Hydrangea paniculata
  • Hydrangea flowers from Kerala, India
  • Hydrangeas in front of the Office de Tourisme Building in Chartres, France.
  • Hydrangea flowers at the "Cerro El Avila" National Park, Venezuela.
  • Hydrangea flowers, Srinagar, Kashmir, India.
  • Hydrangea flowers
  • Hydrangea flowers in Petrópolis, Brazil.
  • Hydrangeas near the Black Lake of Gramado, southern Brazil.
  • Purple hydrangea flowers
  • Hydrangea arborescens leaf

Diseases
Main article: List of hydrangea diseases

Notes
  1. Sunset Western Garden Book, 1995:606–607
  2. "The United States National Arboretum: Hydrangea FAQ". Archived from the original on 2013-05-16. Retrieved 2008-11-27.
  3. Gledhill, David (2008). "The Names of Plants". Cambridge University Press. ISBN 9780521866453 (hardback), ISBN 9780521685535 (paperback). pp 50, 206
  4. "hortensia | Definition of hortensia in English by Oxford Dictionaries". Oxford Dictionaries | English. Retrieved 2017-12-07.
  5. Kyle (2018-09-13). "Scentales | Florist Best Kept Secret: How to Save Wilting Hydrangeas". Scentales Florist. Retrieved 2019-11-25.
  6. "Publications - UGA Cooperative Extension". www.caes.uga.edu. Retrieved 31 May 2018.
  7. "USDA: Hydrangea Questions and Answers". Archived from the original on 16 May 2013. Retrieved 31 May 2018.
  8. "Hydrangea". Encyclopædia Britannica 1911. Retrieved 2014-01-17..
  9. "Hydrangea Plants".
  10. Hollick, Arthur (1925). "A New Fossil Species of Hydrangea". Bulletin of the Torrey Botanical Club. 52 (1): 21–22. doi:10.2307/2479996. JSTOR 2479996.
  11. Łańcucka-Środoniowa M.: Macroscopic plant remains from the freshwater Miocene of the Nowy Sącz Basin (West Carpathians, Poland) [Szczątki makroskopowe roślin z miocenu słodkowodnego Kotliny Sądeckiej (Karpaty Zachodnie, Polska)]. Acta Palaeobotanica 1979 20 (1): 3-117.
  12. "The Complete Guide to All Hydrangea Types | Plant Addicts". plantaddicts.com. Retrieved 2017-11-20.
  13. PDR for Herbal Medicine 3rd Edition Page 453
  14. "Hills of Snow". Retrieved 31 May 2018.
  15. "Erowid Hydrangea Vault". www.erowid.org. Retrieved 31 May 2018.
  16. Willsher, Kim (6 February 2014). "High danger hydrangea? French police hunt gang peddling 'cheaper weed'". the Guardian. Retrieved 31 May 2018.
  17. "Everything You Need to Know About Hydrangeas". www.gardenista.com. 2018-06-10. Retrieved 15 June 2018.
  18. "Hydrangeas: How To Change Color from Pink to Blue". www.gardenista.com. 2016-05-10. Retrieved 15 June 2018.
  19. "This plant has been named 'plant of the year' at the Chelsea Flower Show". 2018-05-22. Retrieved 31 May 2018.
  20. "Hydrangeas, Hydrangeas, Hydrangeas - Roll Gardening & Green :: Roll Magazine: Creative Living in the Hudson Valley". www.rollmagazine.com. Retrieved 31 May 2018.
  21. State Botanical SymbolsBy Alan McPherson, p.3

References
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