Geography and distribution
Sunflower was first domesticated from its wild ancestor more than 5,000 years ago in the south-western part of the USA and, within a short period of time, became widespread throughout the Americas. Its value as an ornamental plant and use as a source of food and oil attracted the attention of European explorers who brought the crop to Europe in the 16th century.
By the 19th century sunflower was being cultivated on a wide scale in Russia, the Ukraine and Caucasus regions for the manufacture of edible vegetable oil. The crop is still important in that part of the world today along with the US and Argentina. Other key producers are India, China, Turkey, the European Union (eg France, Spain) and South Africa. Occasionally, sunflower escapes cultivation and becomes naturalized.
Cultivated in relatively cool temperate to warm subtropical climates. Sunflowers can also be grown in the drier tropical regions but are unsuitable for humid environments. They can grow in a wide range of soils from sandy to clayey provided they are deep, free-draining and not acidic.
Overview: Helianthus annuus is an annual herb which grows up to 5 metres tall with a well-developed taproot extending up to 3 metres into the soil. The stem is erect with a slight-to-severe curve below the flower head in mature plants. In many wild types it is branched whereas in cultivated varieties the stem is unbranched.
Leaves: The leaves are positioned opposite each other in the lower part of the plant and higher up the stem they are arranged spirally. Each leaf is hairy, 10–30 × 5–20 cm with toothed margins, and is supported by a long petiole.
Flowers: The inflorescence is a terminal head (capitulum), 10-50 cm in diameter and is surrounded by three rows of bracts (phyllaries). The flower head is comprised of outer yellow ray florets, which serve to attract pollinators, and inner brownish disc florets which are fertile. The inner florets are numerous and are arranged in spiral whorls from the centre of the head. Each floret is about 2 cm long and consists of a 5-lobed, brown or purplish corolla tube and two deciduous bristly scales (pappus), 5 stamens united into a tube and an ovary which is positioned below the flower tube and stamens. The stigma has two curved lobes and there are nectaries at the base of the style.
Fruit: The fruit (known botanically as an achene) is up to 15-25 mm in size and can be white, brown, black or striped.
Sunflower is mainly cultivated for its tasty seeds and versatile oil and to a lesser extent for ornamental purposes.
The seeds yield edible oil, which is excellent quality due to a high proportion of unsaturated fatty acids, near absence of toxic substances, light colour and good flavour. The oil is used for salads, cooking and as an ingredient in the manufacture of margarine. The oil also has some industrial uses as drying oils for paints and varnishes and in the manufacture of soaps and cosmetics as well as a biofuel.
Wild sunflower growing by the roadside (Photo: Matt Lavin)
The by-product of sunflower oil extraction is a high protein meal, which is commonly blended with soyabean meal and used as livestock feed.
Sunflower meal is sometimes used as a substitute for wheat flour in the baking of bread and cakes for human consumption. The indigenous people of North America have a long tradition of using ground sunflower seeds to make bread-like products.
The varieties cultivated for their seeds are much larger than the oil-cultivars and are often black and white striped, are can be eaten directly. In countries like Russia, the sunflower seeds are salted and roasted whole and enjoyed as a delicious savoury snack.
The smaller seeds are widely used in birdseed and in pet food. Some people air-dry the fruiting capitula and hang them upside down or simply leave the fruiting capitula on the plants for bird feed. Sunflower is sometimes cultivated as a forage crop.
Crop wild relatives of sunflower
The Millennium Seed Bank and the Global Crop Diversity Trust are engaged in a ten-year project, called 'Adapting Agriculture to Climate Change'. The project aims to protect, collect and prepare the wild relatives of 29 key food crops, including sunflower, so that they are available to pre-breeders for the development of new varieties that are more resilient to the effects of climate change.
Millennium Seed Bank: Seed storage
The Millennium Seed Bank Partnership aims to save plants worldwide, focusing on those plants which are under threat and those which are of most use in the future. Once seeds have been collected they are dried, packaged and stored at -20°C in our seed bank vault.
Description of seeds: Average 1,000 seed weight = 42 g
Number of seed collections stored in the Millennium Seed Bank: One
Seed storage behaviour: Orthodox. (The seeds of this plant can be dried to low moisture contents without significantly reducing their viability. This means they are suitable for long-term frozen storage such as at the MSB)
Germination testing: Successful
Helianthus annuus is one of the species included in the ‘Difficult Seeds' project because many of its seeds are short-lived and may not survive a long time in storage.
This species at Kew
Pressed and dried specimens of sunflower are held in Kew's Herbarium, where they are available to researchers by appointment. Details and images of some of these specimens can be seen online in Kew's Herbarium Catalogue.