Hydrangea macrophylla (Bigleaf hydrangea)

Hydrangea macrophylla is a species of flowering plant in the family Hydrangeaceae, native to Japan. It is a deciduous shrub growing to 2 m (7 ft) tall by 2.5 m (8 ft) broad with large heads of pink or blue flowers in summer and autumn. Common names include bigleaf hydrangea, French hydrangea, lacecap hydrangea, mophead hydrangea, penny mac and hortensia. It is widely cultivated in many parts of the world in many climates. It is not to be confused with H. aspera 'Macrophylla'.

Description
The term macrophylla means large- or long-leaved. The opposite leaves can grow to 15 cm (6 in) in length. They are simple, membranous, orbicular to elliptic and acuminate. They are generally serrated.

The inflorescence of Hydrangea macrophylla is a corymb, with all flowers placed in a plane or a hemisphere or even a whole sphere in cultivated forms. Two distinct types of flowers can be identified: central non-ornamental fertile flowers and peripheral ornamental flowers, usually described as "sterile". A study of several cultivars showed that all the flowers were fertile but the non-ornamental flowers were pentamers while the decorative flowers were tetramers. The four sepals of decorative flowers have colors ranging from pale pink to red fuchsia purple to blue. The non-decorative flowers have five small greenish sepals and five small petals. Flowering lasts from early summer to early winter. The fruit is a subglobose capsule.

Distribution and habitat
Hydrangea macrophylla is native to Japan and possibly Korea. It is reported from seaside habitats as well as mountains in Japan, from Honshu southwards. This species has naturalized in China, New Zealand and the Americas.

Colors and soil acidity
Hydrangea macrophylla blooms can be blue, red, pink, light purple, or dark purple. The color is affected by soil pH. An acidic soil (pH below 7) will usually produce flower color closer to blue, whereas an alkaline soil (pH above 7) will produce flowers more pink. 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.

Landscaping
In climates where Hydrangea macrophylla flowers, place in a mixed shrub border or at the back of a flower bed. Its rich foliage and large size make it a wonderful background for white or light colored flowers, even tall growing perennials and annuals. In warm climates H. macrophylla is good for adding a splash of early summer color to shady areas and woodland gardens. Minimal pruning is recommended for most prolific flowering. Flowers are easily air dried and are long lasting.

While Hydrangea macrophylla is not considered a particularly difficult plant to grow, it may fail to flower. This may be due to cold winter damage to the flower buds, not getting enough sunlight, too much nitrogen fertilizer, or pruning at the wrong time of year. H. macrophylla forms flower buds in late summer. As a result, pruning in late summer, fall or winter could remove potential flowers.

Chemistry
Phyllodulcin, hydrangenol, and their 8-O-glucosides, and thunberginols A and F can be found in H. macrophylla. Thunberginol B, the dihydroisocoumarins thunberginol C, D and E, the dihydroisocoumarin glycosides thunberginol G 3'-O-glucoside and (−)-hydrangenol 4'-O-glucoside and four kaempferol and quercetin oligoglycosides can be found in Hydrangeae Dulcis Folium, the processed leaves of H. macrophylla var. thunbergii. The leaves also contain the stilbenoid hydrangeic acid.

The various colors, such as red, mauve, purple, violet and blue, in H. macrophylla are developed from one simple anthocyanin, delphinidin 3-glucoside (myrtillin), which forms complexes with metal ions called metalloanthocyanins.

Lunularic acid, lunularin, 3,4′-dihydroxystilbene and a glycoside of lunularic acid have been found in the roots of H. macrophylla.

Hydrangine is another name for the coumarin umbelliferone, and may be responsible for the possible toxicity of the plant.
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