A little botany

The name 'hydrangea' comes from the form of the plants' fruit, which has the shape of an antique water vessel ( hydrangea derives  from the Greek words hydor, 'water', and aggeion, 'receptacle' ) 

Hydrangeas are best known through the species H.macrophylla and its hybrids, which have globular inflorescences, known in French and several other European languages as 'hortensias'. Many authors believed that the plant had been named as a tribute to a woman called 'Hortense', but in fact it was first given by Philibert Commerson to a hydrangea macrophylla with globular inflorescences which he found in the garden of the king of Bourbon Island ( Réunion ). In fact, in Latin the word 'hortensia' means 'from the garden'.

 Morphological characteristics

Hydrangeas are woody shrubs, meaning they retain their branches in winter. Most are of upright habit. The largest can grow to ten metres in height, while the smallest are less than a metre tall.There are some climbing species which attach themselves to their support with aerial roots ; these can grow to a height of over twenty metres above ground level. Leaves, which are generally deciduous in garden plants, are always opposite and never alternate. Old bark flakes off in all species.

Fertile flowers and sterile florets : Hydrangeas do not bear single flowers, but flower heads called inflorescences containing two sorts of flowers : fertile flowers, which are unspectacular and measure only a few millimetres in height, and sterile florets, which are often from one to three centimetres in diameter. It is these which give the inflorescence their decorative value ; the coloured sepals are much more highly developed than the petals.

Inflorescence shape : depending on the species, inflorescences can have the shape of 'lacecaps', 'mopheads' or 'panicles'.

                                    

            lacecap                     panicle                      mophead

Inflorescence colour : the colour of hydrangea inflorescences is confined to a single range : from blue to red, passing through all the possible intermediate colours, from the lightest to the darkest. In coloured species, the colour is extremely variable, depending on soil acidity. In very acid soil, flowers are blue. In less acid soil, flowers are purple or mauve. In almost neutral soil, flowers are red or pink.In fact it is not the acidity of the soil itself which turns the colour blue, but the aluminium in the soil which can only be absorbed in acid conditions.

To find out much more, read the books by Corinne Mallet ( see the Corinne Mallet page ).                 

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