Hydrangea ( or Sunset Western Garden Book, 1995: 606–607) 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 tall, but some are small trees, and others lianas reaching up to 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.
Etymology Hydrangea is derived from Greek and means 'water vessel' (from húdōr "water" + ángos or angeîon "vessel"), in reference to the shape of its seed capsules. The earlier name, Hortensia, is a Latinised version of the French given name Hortense. Philibert Commerson had attempted to call the flower Lepautia or Peautia in honor of French astronomer and mathematician Nicole-Reine Lepaute, but the common name for the flower instead became Hortensia. This led people to believe that Lepaute's name was Hortense, but the Larousse remarks that this is erroneous, and that the name probably came from hortus, garden.
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 fertile flowers in the center or interior of the flowerhead, and large, sterile 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.
Colors and soil acidity
Hydrangea flower color can change based on the pH in soil. As the graph depicts, soil with a pH of 5.5 or lower will produce blue flowers, 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 color-manipulated by soil pH because they do not produce pigment for color. In other words, while the hue of the inflorescence is variable dependent upon cultural factors, the color saturation is genetically predetermined. In most species, the flowers are white. In some, however, (notably H. macrophylla), they can be blue, red, or purple, with color saturation levels ranging from the palest of pinks, lavenders & powder blues, to deep, rich purples, reds, and royal blues. In these species, floral color change occurs due to the availability of aluminium ions, a variable which itself depends upon the soil pH. 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 aluminium ions and typically produce flowers that are blue to purple,. whereas an alkaline soil (pH above 7) will tie up aluminium 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.
Species
98 species are accepted.
Hydrangea acuminata Hydrangea albostellata Hydrangea alternifolia Hydrangea × amagiana Hydrangea amamiohsimensis Hydrangea ampla Hydrangea anomala – (climbing hydrangea) Himalaya, southwest China Hydrangea arborescens – (smooth hydrangea) eastern North America Hydrangea arguta – Hawaii Hydrangea aspera – China, Himalaya Hydrangea asterolasia Hydrangea barbara Hydrangea bifida Hydrangea breedlovei Hydrangea bretschneideri – China Hydrangea caerulea Hydrangea carroniae Hydrangea chungii – China Hydrangea cinerea – (ashy hydrangea) eastern United States Hydrangea coenobialis – China Hydrangea corylifolia Hydrangea crassa Hydrangea daimingshanensis Hydrangea davidii – China Hydrangea densifolia Hydrangea diplostemona Hydrangea fauriei Hydrangea febrifuga (syn. Dichroa febrifuga) – central & southern China to Malesia and New Guinea Hydrangea glaucescens – China, Myanmar and Vietnam Hydrangea gracilis – China Hydrangea heteromalla – Himalaya, west and north China Hydrangea hirsuta Hydrangea hirta – Japan Hydrangea hwangii Hydrangea hydrangeoides – Ulleungdo, Japan, Kurils Hydrangea hypoglauca – China Hydrangea integrifolia – China Hydrangea involucrata – Japan, Taiwan Hydrangea jelskii – Andes Hydrangea kawagoeana Hydrangea kwangsiensis – China Hydrangea kwangtungensis – China Hydrangea lalashanensis Hydrangea lingii – China Hydrangea linkweiensis – China Hydrangea liukiuensis Hydrangea lobbii Hydrangea longifolia – China Hydrangea longipes – western China Hydrangea luteovenosa Hydrangea macrocarpa – China Hydrangea macrophylla – (bigleaf hydrangea) southeast Japan, southern China Hydrangea mangshanensis – China Hydrangea marunoi Hydrangea mathewsii Hydrangea megalocarpa Hydrangea minamitanii Hydrangea × mizushimarum Hydrangea moellendorffii Hydrangea mollissima Hydrangea nahaensis Hydrangea nebulicola Hydrangea obtusifolia Hydrangea ofeliae Hydrangea otontepecensis Hydrangea paniculata – (panicled hydrangea) eastern China, Japan, Korea, Sakhalin Hydrangea peruviana – Costa Rica and Panama, Andes Hydrangea petiolaris – (climbing hydrangea) Japan, Korea, Sakhalin Hydrangea pingtungensis Hydrangea platyarguta Hydrangea pottingeri (synonym Hydrangea chinensis ) – Arunachal Pradesh, Myanmar, southeastern China, and Taiwan Hydrangea preslii Hydrangea quercifolia – (oakleaf hydrangea) southeast United States Hydrangea radiata – (silverleaf hydrangea) southeast United States Hydrangea robusta – China, Himalaya Hydrangea sargentiana – western China Hydrangea scandens – southern Japan south to the Philippines Hydrangea seemannii - northern Mexico, to Nayarit Hydrangea serrata – Japan, Korea Hydrangea serratifolia – Chile, western Argentina Hydrangea sikokiana Hydrangea sousae Hydrangea steyermarkii Hydrangea strigosa – China Hydrangea stylosa – China Hydrangea taiwaniana Hydrangea tapalapensis Hydrangea tarapotensis – Andes Hydrangea tomentella Hydrangea × versicolor Hydrangea viburnoides Hydrangea wallichii Hydrangea xanthoneura – China Hydrangea xinfeniae Hydrangea yaoshanensis Hydrangea yayeyamensis Hydrangea × ytiensis Hydrangea yunnanensis Hydrangea zhewanensis – China
Fossil record
Hydrangea alaskana is a fossil species recovered from Paleogene strata at Jaw Mountain Alaska. †Hydrangea knowltoni has been described from leaves and flowers recovered from the Miocene Langhian Latah Formation of the inland Pacific Northwest United states. The related Miocene species †Hydrangea bendirei is known to from the Mascall Formation in Oregon, and †Hydrangea reticulata is documented from the Weaverville Formation in California.
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.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.
Cultivation and uses Hydrangeas are popular ornamental plants, grown for their large flowerheads, with Hydrangea macrophylla being by far the most widely grown. It has 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 and lacecap hydrangea. 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.
The following cultivars and species have gained the Royal Horticultural Society's Award of Garden Merit under the synonym Schizophragma: S. hydrangeoides var. concolor 'Moonlight' S. hydrangeoides var. hydrangeoides 'Roseum' S. integrifolium
Hydrangea root and rhizome are indicated for the treatment of conditions of the urinary tract in the Physicians' Desk Reference for Herbal Medicine and may have diuretic properties.PDR for Herbal Medicine 3rd Edition Page 453 Hydrangeas are moderately toxic if eaten, with all parts of the plant containing cyanogenic glycosides. Hydrangea paniculata is reportedly sometimes smoked as an intoxicant, despite the danger of illness and/or death due to the cyanide.
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. Adding organic materials such as coffee grounds and citrus peel will increase acidity and turn hydrangea flowers blue. A popular pink hydrangea called Vanilla Strawberry has been named "Top Plant" by the American Nursery and Landscape Association.
A hybrid "Runaway Bride Snow White", from Japan, won Plant of the Year at the 2018 RHS Chelsea Flower Show.
In culture In Japan, ama-cha (), 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 is used for an herbal tea called sugukcha () or isulcha ().
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 Korean florist Tan Jun Yong, who 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!"
Hydrangea quercifolia was declared the official state wildflower of the U.S. state of Alabama in 1999.State Botanical SymbolsBy Alan McPherson, p.3
Hydrangeas were used by the Cherokee people of what is now the Southern U.S. as a mild diuretic and cathartic; it was considered a valuable remedy for bladder stones.
Extrafloral nectaries were reported on hydrangea species by Zimmerman 1932, but Elias 1983 regards this as "doubtful".