Sunflower

Sunflower (Helianthus) is a species of large annual forb of the daisy family Asteraceae. Sunflowers are native primarily to North and South America and edible oily seeds are used for cooking oil. The oil is also used in soap and paints and as a lubricant. The seeds may be eaten dried, roasted, or ground into nut butter and are common in birdseed mixes.

## Common sunflower

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The common sunflower (Helianthus annuus) has a green erect stem covered in coarse hairs, growing on average around 2m tall. The leaves are broad, with serrated edges, and are alternately arranged on the stem. The ‘flower’ of the common sunflower is actually a pseudanthium, or flowerhead, made up of many small flowers. The outer yellow ‘petals’ on the flowerhead are known as ray flowers and are made up of multiple petals fused together. Ray petals are usually yellow but can sometimes be red or orange. The black-brown flowers in the centre of the head, called disk flowers, grow in a spiral formation, and mature into sunflower seeds over time.

## Planting

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Sunflowers are annual plants that perform best in sunny locations. They can be easily started from seed by directly placing seeds into the ground. Sunflowers can also be started indoors as transplants, which allows for them to bloom earlier than direct seeding.

## Interactions

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Sunflower probably represents a classic case in the evolution of crops. It is a 'weedy' species in an ecological sense, one that thrives in disturbed habitats. Because of this, it probably frequented the areas close to primitive human habitation. Subsequently humans recognized its utility and started actively cultivating it and thereby developing it as a crop. A similar scenario may also apply to wheat and other crop species.