Sunflower scientifically known as Helianthus annuus is an annual plant in the family Asteraceae, with a large flower head (capitulum). The central florets look like the centre of a normal flower, and the outer florets look like yellow petals.
All together they make up a “false flower” or pseudanthium. The benefit to the plant is that it is very easily seen by the insects and birds which pollinate it, and it produces thousands of seeds.
Generally, each floret is oriented toward the next by approximately the golden angle, 137.5°, producing a pattern of interconnecting spirals, where the number of left spirals and the number of right spirals are successive Fibonacci numbers.
Typically, there are 34 spirals in one direction and 55 in the other; on a very large sunflower there could be 89 in one direction and 144 in the other.
In Germany, it is mixed together with rye flour to make Sonnenblumenkernbrot (literally: sunflower whole seed bread), which is quite popular in German-speaking Europe.
It is also sold as food for birds and can be used directly in cooking and salads. Sunflower oil, extracted from the seeds, is used for cooking, as a carrier oil and to produce margarine and biodiesel, as it is cheaper than olive oil.
A range of sunflower varieties exist with differing fatty acid compositions; some ‘high oleic’ types contain a higher level of healthy monounsaturated fats in their oil than Olive oil.
They are distinguished technically by the fact that the ray florets (when present) are sterile, and by the presence on the disk flowers of a pappus that is of two awn-like scales that are caducous (that is, easily detached and falling at maturity).
Some species also have additional shorter scales in the pappus, and there is one species that lacks a pappus entirely.
Another technical feature that distinguishes the genus more reliably, but requires a microscope to see, is the presence of a prominent, multicellular appendage at the apex of the style.
Sunflowers are especially well known for their symmetry based on Fibonacci numbers and the Golden angle.
Sunflowers are generally hardy plants and can withstand short dry or wet spells. It’s important that they are not overwatered, as this loosens the soil to the point that they cannot support the weight of the large flowers heads.
Seedlings need to be protected from snails until they are about ten centimetres high. Tall plants can be stabilised by tying individual plants to supporting sticks.