Helianthus annuus, Common Sunflower,
Hebrew: חמנית מצויה, Arabic: دوار الشمس

Scientific name:  Helianthus annuus L.
Common name  Common Sunflower
Hebrew name:   חמנית מצויה
Arabic name:  دوار الشمس
Plant Family:  Compositae / Asteraceae, מורכבים

ישראל, פרחים, צמי בר, תמונות, חמנית מצויה

Life form:  Annual
Stems:  100–300 cm; erect, rough, hairy
Leaves:  Alternate, entire, dentate or serrate margin; rough on both sides
Inflorescence:  Involucrate capitulum, a large flowering head
Flowers:  Yellow ray-florets; disk-florets, bisexual, fertile, yellow, brown, purplish
Fruits / pods:  Cypsela, edible seed
Flowering Period:   May, June, July, August, September
Habitat:  Disturbed habitats
Distribution:   Mediterranean Woodlands and Shrublands, Semi-steppe shrublands
Chorotype:  American
Summer shedding:  Ephemeral

Helianthus annuus, Common Sunflower,دوار الشمس , חמנית מצויה

Derivation of the botanical name:
Helianthus, Greek helios, the sun; anthos, a flower; sunflower.
annuus, annual.
  • The standard author abbreviation L. is used to indicate Carl Linnaeus (1707 – 1778), a Swedish botanist, physician, and zoologist, the father of modern taxonomy.
Sunflowers in the bud stage exhibit heliotropism (the diurnal motion of plant parts (flowers or leaves) in response to the direction of the sun). At sunrise, the faces of most sunflowers are turned towards the east. Over the course of the day, they follow the sun from east to west, while at night they return to an eastward orientation.
When one observes the heads of sunflowers, one notices two series of curves, one winding in one sense and one in another; the number of spirals not being the same in each sense.
The number of spirals is in general either 21 and 34, either 34 and 55, either 55 and 89, or 89 and 144. They all belong to the Fibonacci sequence: 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, etc.
The Fibonacci numbers fn are given by the formula f1 = 1, f2 = 2, f3 = 3, f4 = 5 and generally f n+2 = fn+1 + fn .
In order to optimize the filling, it is necessary to choose the most irrational number there is, that is to say, the one the least well approximated by a fraction. This number is exactly the Golden Mean, or the Golden Ratio (The Golden Ratio is an irrational number approximating 1.6180). The corresponding angle, the golden angle, is 137.5 degrees. (It is obtained by multiplying the non-whole part of the golden mean by 360 degrees and, since one obtains an angle greater than 180 degrees, by taking its complement). With this angle, one obtains the optimal filling, that is, the same spacing between all the seeds. This arrangement forms an optimal packing of the seeds.

Helianthus annuus, Common Sunflower, חמנית מצויה

Helianthus annuus, Common Sunflower, دوار الشمس,חמנית מצויה

Flora of Israel online