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Helianthus annuus

Daisy Family [Asteraceae]  

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11th Aug 2009, Clitheroe, Lancs. Photo: © RWD
Before fully opening the innards and bracts (actually phyllaries) may be charcoal coloured.

11th Aug 2009, Clitheroe, Lancs. Photo: © RWD
There are two or more layers of ovate (with long pointed tip) phyllaries enclosing the central florets that you normally do not see when the flower is opened for they will then be behind the flower.

11th Aug 2009, Clitheroe, Lancs. Photo: © RWD
A closer view of the layers of charcoal-coloured phyllaries, longer hairs on the edge; much shorter elsewhere.

18th August 2008, St. Julien d'Eymet, Dordogne. Photo: © Christine Shield
They all face the same direction.

30th July 2009, Kingsley, Staffordshire. Photo: © RWD
Grows up to 3m tall. Leaves sparse up the stem.

30th July 2009, Kingsley, Staffordshire. Photo: © RWD
Flowers a very large 10 to 30cm across. The leaves broad, large and heart-shaped.

4th Aug 2009, Walkden Railway Station, Greater Manchester. Photo: © RWD
The central brownish florets occupy a third of the diameter.

30th July 2009, Kingsley, Staffordshire. Photo: © RWD
Phyllaries behind the flowerhead are abruptly pointed. The stem (and leaves) have rough hairs which are actually trichomes.

4th Aug 2009, Walkden Railway Station, Greater Manchester. Photo: © RWD
Central disc florets are brown to black.

30th July 2009, Kingsley, Staffordshire. Photo: © RWD
The petals (ray florets) deep yellow. Leaves have un-even teeth.

4th Aug 2009, Walkden Railway Station, Greater Manchester. Photo: © RWD
The pollen yellow within 5-starred disc florets.

16th Sept 2009, Silverdale, Lancs. Photo: © RWD
The un-opened inner disc florets, greenish looking. Note the flat 'lips'.

16th Sept 2009, Silverdale, Lancs. Photo: © RWD
The partially opened inner disc florets.

17th sept 2009, Eagle & Child, Bispham Green, Burscough. Photo: © RWD
The outer 5-starred disc florets.

Some similarities to : Perennial Sunflower but Perennial Sunflower is only half as tall, has much narrower leaves, fewer and wider outer petals, a paler-yellow flower less than half as large and a disproportionately smaller central floret area.

Uniquely identifiable characteristics.

Distinguishing Feature : The tallest yellow-flowered plant in the U.K. Specimens have been known to grow to a height of 8m, but this is very unusual, normal height being about 2m.

Grown mainly in gardens for show or competitions.


Grown commercially to yield sunflower oil (which is obtained from the seeds) and is used in cooking. Sunflower oil has varying proportions of the fatty acids linoleic, oleic, stearic and palmitic acids, depending upon the type of Sunflower from which it is derived, with the most predominant first and the least dominant last. Linoleic (not to be confused with Linolenic Acid) is doubly unsaturated, oleic singly un-saturated. Both stearic and palmitic acids are saturated fats and attempts are made to minimise these when the seeds are to be used for producing healthy cooking oil.

The first three fatty acids have 18 carbon atoms, Palmitic Acid has only 16.

A durable yellow dye used to be extracted from the ray florets once used by the Hopi Indians. A near-black or dull-blue dye can be made from the seeds.


Sunflowers are heliotropic (pointing towards the sun and following its progress across the sky) only when in the bud stage but not when in flower. When they set flower they affix themselves to point in one direction only, usually towards the morning Sun (East), thus protected from the seeds from the full blaze of the midday sun. The bees which help pollinate the flowers will only visit those flowers pointing towards the East and not those pointing any other direction. Thus the ripened seeds pollinated by bees will, over time, actively select for those plant genetics which give rise to this plant behaviour.

The heliotropic response is mediated by one of the plant hormones, Indole-3-Acetic Acid (aka 3-Indolylacetic Acid or IAA) which is a heteroauxin or Plant Growth Regulator. Indole-3-Acetic Acid is a light sensitive hormone which causes the cell to grow in an asymmetric fashion, elongating it. It is this aligned elongation which causes the flower to turn, nominally towards the source of the strong light, the sun. It seems that another auxin, Indole-3-acetonitrile (aka 3-Indolylacetonitrile or IAN), which has an inhibitory effect on asymmetrical cell growth may also be involved.

Heliotropism is an example of photonasty, where it is light that activates some movement in the plant. Other flowers accomplish the opening and closing of flowers or other parts of the plant by differing means, such as by either Tropic movements or by Nastic movements. Nastic movements are initiated by various stimuli, thus Chemonasty is initiated by soil chemicals or nutrients, Epinasty (by gravity), Geonasty (by gravity), Hydronasty (by water), Hyponasty (by the growth hormone Ethylene), Nyctonasty (by circadian clock and light), Photonasty (by light), Thermonasty (by heat) and Thigmonasty (by touch). Thigmomorphogenesis is the alteration of parts of a plants genome in order to facilitate the Thigmonastic defence response.

Famous for displaying Fibonacci spirals, where there are typically 34 seeds in the spiral in one direction, and 55 seeds in the other direction, both Fibonacci Numbers. The Fibonacci mathematical sequence begins with the numbers 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89...

Annual Sunflower contains the toxic Sesquiterpene Lactone Niveusin A (as well as seven more toxic Niveusin A derivatives) which are contained in and around the trichomes present on both leaves and stem. These trichomes release the toxins when handled, and can result in dermatitis, which has been known of for centuries regarding Annual Sunflowers.

Annual Sunflower also has the ability to tolerate normally toxic metals in the soil, in fact it not only tolerates them but hyperaccumulates them. It is thus a valuable metallophyte for the phytoremediation of contaminated land, able to mop up a variety of metals from the soil including arsenic and zinc. Annual Sunflower (and Maize (Zea mays)) will also hyperaccumulate radioactive   Caesium-137 and radioactive   Strontium-90 released in the nuclear fallout from the   Chernoble Nuclear Reactor accident. Note that to remove the metals entirely, the plant then has to be harvested and disposed of safely elsewhere. The whole cycle has to be repeated over several seasons to bring heavy metal contamination down to safe levels. This could take many years.

It will accumulate up to 8 times more caesium-137 than do either Foxtail or Timothy grasses. Most of the caesium is contained in the roots of Annual Sunflower, up to 3 times more than in the above ground aerial parts of the plant. Of course, it is not fussy, it will hyperaccumulate caesium or strontium whether or not they are present as radioactive isotopes or as completely stable isotopes, such as from the exhaust ashes of coloured fireworks [which may contain oxides of   strontium (for red sparks) or of   caesium (for blue-violet) or of   barium (for green), etc].

  Helianthus annuus  ⇐ Global Aspect ⇒ Asteraceae  

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Helianthus annuus

Daisy Family [Asteraceae]  

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