Hydrangea is a flowering plant found in different parts of the world in many different climates. Some species are native to China. The Chinese names of the flowers are 繡球花, 八仙花, 紫陽花, etc. It is a deciduous shrub growing to 2 m tall by 2.5 m broad with large heads of pink, blue or white flowers in late spring and summer.

The inflorescence of Hydrangea is a corymb, with all flowers placed in 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”. Some ornamental varieties are all sterile. More studies on the floral structures will be done later on.

Flowering lasts from early summer to early winter. The fruit is a subglobose capsule.

Hydrangeas are amazingly versatile in that you can actually alter the flower colours to suit your needs. The flower colour in most forms relates to the acidity or alkalinity of the soil. In acid soil (pH 5 or less) hydrangeas are usually always blue. As the soil pH climbs towards the neutral and alkaline end of the scale (pH 7 or more) hydrangeas turn mauve, pink and red. A blueing tonic (containing aluminium and iron) will turn pink or mauve hydrangeas blue. A cup of lime (calcium carbonate) added to the soil in spring will cause blue or mauve hydrangeas to turn pink. White flowering hydrangeas will remain white regardless of soil pH.

However, in my garden a purple flower plant is planted together with a pinkish-blue flower plant under soil of the same pH, their different phenotypes can still be expressed.

A purple flower plant is planted together with a pink flower plant under soil of the same pH, their different phenotypes can still be expressed differently.
Two  different phenotypes can still be expressed when grown in soil of the same pH. 

Before next Spring, I will adjust the pH of the soil and see if the plants will change the colour of the flowers.

 

Development of the Hydrangea inflorescence

Young inflorescence of Hydrangea
Buds of the inflorescence
Young inflorescence of Hydrangea developing
Young inflorescence developing
Inflorescence of Hydrangea with white 'flowers'. (Please note the white structures are not petals!)
Inflorescence with white ‘flowers’. (The white structures are not petals, they are sepals! ) At this stage, no stamens and pistils are visible, some botanists named these flowers as ‘neutral flowers‘ as no male parts or female parts are shown..

 

Close-up view of the white inflorescence

The middle small purple structure is the real flower of the inflorescence. There are a few real flowers in each inflorescence.
Among the neutral flowers, there are a few tiny purple ‘typical’ flowers in the inflorescence.

‘Typical’ flowers

The purple flower has 5 purple petals, 5 sepals, 10 stamens and 3 stigmas.
The purple flower has 5 relatively bigger purple petals, 5 relatively smaller white sepals, 10 stamens and 3 stigmas.

 

Stamens of the flower
Stamens of the flower
3 stigmas of the flower
3 stigmas of the flower
The ovary has been cut opened to show the ovules.
The ovary has been cut opened to show the ovules.
The flower as seen from the bottom: 5 sepals alternate with 5 purple coloured petals, the ovary has been cut opened to shows 3 carpels with ovules inside.
The flower as seen from the bottom: 5 sepals alternate with 5 purple coloured petals, the ovary has been cut opened to shows 3 carpels with ovules inside.

 

Neutral flowers

Many botanists consider those flowers where stamens and pistils are under developed and lack function as neutral flower. However, near the end of the life of the white flowers, the petals eventually open and the stamens and pistil are exposed.

 

The white 'flower' has 4 petal-like structures. They may be sepals of the flower. The middle part of the flower has a purple coloured structure which remained closed.
The white ‘flower’ has 4 sepals. The middle part of the flower has a purple coloured structure which remained closed.
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The purple coloured structure as seen under the microscope
When the purple coloured structure has been cut opened, 8 stamens and 3 stigmas can be seen. The purple coloured structure may be 4 petals and the white petal-like structures may be sepals. (Further investigation is needed.)
When the purple coloured structure has been cut opened by a razor blade, 8 stamens and 3 stigmas can be seen. The purple coloured structure are the 4 petals and the white structures are the sepals.
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After many days the purple petals eventually open and the stamens and pistil are exposed.

 

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Even after the white sepals have started to wither, the little purple flowers still bloom.

 

No development of the flowers into fruits have been observed in these commercial varieties of Hydrangea.

 

Young inflorescence of Hydrangea with lilac ‘flowers’

Inflorescence of Hydrangea with lilac 'flowers'
Young inflorescence of Hydrangea with lilac ‘flowers’
Most of the flowers are in full bloom, some flowers start to wither
Mature inflorescence, some flowers start to wither. The petals in the neutral flowers have not yet opened.

 

Chinese drawings / paintings on Hydrangea 

Zhou Zhimian (周之冕) (b 1520), a small section of a long scroll of flower painting (百卉圖), ink and Chinese watercolour on paper, 32 x 171.7 cm
Zhou Zhimian (周之冕) (b 1520), a small section of a long scroll of flower painting (百卉圖), ink and Chinese watercolour on paper, 32 x 171.7 cm
Zhou Zhimian (周之冕) (b 1520), a small section of a long scroll of flower painting (百卉圖), ink and Chinese watercolour on paper, 32 x 171.7 cm
Zhou Zhimian (周之冕) (b 1520), a small section of a long scroll of flower painting (百卉圖), ink and Chinese watercolour on paper, 32 x 171.7 cm

 

Artist: Shitao (1642 - 1707), dated 1694, ink on paper, album 31.2 x 20.4 cm, Shanghai Museum
Artist: Shitao (1642 – 1707), dated 1694, ink on paper, album 31.2 x 20.4 cm, Shanghai Museum
Shitao (1642 - 1707), dated 1694, ink on paper, album 31.2 x 20.4 cm, Shanghai Museum
Details of the above painting by Shitao

 

Chao Shao-ang (趙少昂) (1905 – 1998), ink and Chinese watercolour on paper
Chao Shao-ang (趙少昂) (1905 – 1998,) Hydrangea, ink and Chinese watercolour on paper

 

Chao Shao-ang (趙少昂) (1905 – 1998), ink and Chinese watercolour on paper
Chao Shao-ang (趙少昂) (1905 – 1998), Hydrangea and Honey Bees, ink and Chinese watercolour on paper

 

 

Chao Shao-ang (趙少昂) (1905 – 1998), a sketch of Hydrangea
Chao Shao-ang (趙少昂) (1905 – 1998), a sketch of Hydrangea

 

Oil painting on Hydrangea

Allan Hansen, circa 1993, oil on canvas, 34 x 46 cm
Allan Hansen, Hydrangea, circa 1993, oil on canvas, 34 x 46 cm

 

Michelle Holmes, 2015, watercolour on paper, 59 x 43 cm (Courtesy of Michelle)
Michelle Holmes, Hydrangea, 2015, watercolour on paper, 59 x 43 cm (Courtesy of Michelle)

 

 

Bibliography:

https://en.wikipedia.org/wiki/Hydrangea_macrophylla

http://www.burkesbackyard.com.au/fact-sheets/in-the-garden/flowering-plants-shrubs/hydrangeas/#.VjVLQ7crIgs

Chao Shao-ang (趙少昂) (1990) A Study of Chinese Paintings, Publisher: Ho Kung-shang, Art Book Co., Ltd, Taiwan, ISBN 957-9045-22-4

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