Helianthus annuus

Helianthus annuus, the common sunflower, is a large annual forb of the genus Helianthus grown as a crop for its edible oil and edible fruits. This sunflower species is also used as wild bird food, as livestock forage (as a meal or a silage plant), in some industrial applications, and as an ornamental in domestic gardens. The plant was first domesticated in the Americas. Wild Helianthus annuus is a widely branched annual plant with many flower heads. The domestic sunflower, however, often possesses only a single large inflorescence (flower head) atop an unbranched stem. The name sunflower may derive from the flower's head's shape, which resembles the sun, or from the impression that the blooming plant appears to slowly turn its flower towards the sun as the latter moves across the sky on a daily basis. Sunflower seeds were brought to Europe from the Americas in the 16th century, where, along with sunflower oil, they became a widespread cooking ingredient. The plant has an erect rough-hairy stem, reaching typical heights of 3 metres (9.8 ft). The tallest sunflower on record achieved 9.17 metres (30.1 ft). Sunflower leaves are broad, coarsely toothed, rough and mostly alternate. What is often called the 'flower' of the sunflower is actually a 'flower head' or pseudanthium of numerous small individual five-petaled flowers ('florets'). The outer flowers, which resemble petals, are called ray flowers. Each 'petal' consists of a ligule composed of fused petals of an asymmetrical ray flower. They are sexually sterile and may be yellow, red, orange, or other colors. The flowers in the center of the head are called disk flowers. These mature into fruit (sunflower 'seeds'). The disk flowers are arranged spirally. 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; however, in a very large sunflower head there could be 89 in one direction and 144 in the other. This pattern produces the most efficient packing of seeds mathematically possible within the flower head. Most cultivars of sunflower are variants of Helianthus annuus, but four other species (all perennials) are also domesticated. This includes H. tuberosus, the Jerusalem artichoke, which produces edible tubers. A model for the pattern of florets in the head of a sunflower was proposed by H. Vogel in 1979. This is expressed in polar coordinates where θ is the angle, r is the radius or distance from the center, and n is the index number of the floret and c is a constant scaling factor. It is a form of Fermat's spiral. The angle 137.5° is related to the golden ratio (55/144 of a circular angle, where 55 and 144 are Fibonacci numbers) and gives a close packing of florets. This model has been used to produce computer graphics representations of sunflowers. The sunflower, Helianthus annuus, genome is diploid with a base chromosome number of 17 and an estimated genome size of 2871–3189 Mbp. Some sources claim its true size is around 3.5 billion base pairs (slightly larger than the human genome). To grow best, sunflowers need full sun. They grow best in fertile, moist, well-drained soil with heavy mulch. In commercial planting, seeds are planted 45 cm (1.48 ft) apart and 2.5 cm (0.98 in) deep.Sunflower 'whole seed' (fruit) are sold as a snack food, raw or after roasting in ovens, with or without salt and/or seasonings added. Sunflowers can be processed into a peanut butter alternative, sunflower butter. In Germany, it is mixed 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. Native Americans had multiple uses for sunflowers in the past, such as in bread, medical ointments, dyes and body paints.