Hydrangea

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{{Taxobox | color = lightgreen | name = Hydrangea | image = Hydrangea hirta 2004ja 01.jpg | image_width = 240px | image_caption = Hydrangea hirta | regnum = Plantae | divisio = Magnoliophyta | classis = Magnoliopsida | ordo = Cornales | familia = Hydrangeaceae | genus = Hydrangea | subdivision_ranks = Species | subdivision = See text }}

Hydrangea (common name also Hydrangea; pronounced haidréindʒiə) is a genus of about 70-75 species of flowering plants native to southern and eastern Asia (from Japan to China, the Himalaya and Indonesia) and North and South America. By far the greatest species diversity is in eastern Asia, notably China and Japan. Most are shrubs 1-3 m tall, but some are small trees, and others lianas reaching up to 30 m by climbing up trees. They can be either deciduous or evergreen, though the widely cultivated temperate species are all deciduous.

Hydrangea flowers are produced from early spring to late autumn; they grow in flowerheads (corymbs or panicles) at the ends of the stems. In many species, the flowerheads contain two types of flowers, small fertile flowers in the middle of the flowerhead, and large, sterile bract-like flowers in a ring around the edge of each flowerhead. Other species have all the flowers fertile and of the same size.

In most species the flowers are white, but in some species (notably H. macrophylla), can be blue, red, pink, or purple. In these species the exact colour often depends on the pH of the soil; acidic soils produce blue flowers, neutral soils produce very pale cream petals, and alkaline soils results in pink or purple. Hydrangeas are one of very few plants that accumulate aluminium. Aluminium is released from acidic soils, and in some species, forms complexes in the hydrangea flower giving them their blue colour.

Selected species
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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. 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 the following season.

Hydrangeas are moderately toxic if eaten, with all parts of the plant containing cyanogenetic glycosides. However, poisoning is rare, as the plant does not look an enticing food source.

A Hydrangea at Watermouth Castle, north Devon, England

Close up of pale big leaf hydrangea flowerheads.

Hydrangea flowerheads (closeup)

A Hydrangea painted by the botanical artist Redouté

Bigleaf Hydrangea

Bigleaf Hydrangea

Bigleaf Hydrangea

Bigleaf Hydrangea

Oakleaf Hydrangea

Oakleaf Hydrangea

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References

de:Hortensien es:Hydrangea eo:Hortensio fr:Hortensia it:Hydrangea nl:Hortensia ja:アジサイ pt:Hortência

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