How big is Sunflower Seed? | Scale of the Universe

A sunflower seed is the fruit of the common sunflower, Helianthus annuus: a hard hull wrapped around a single kernel. The striped seed shown here is 7 millimeters (0.28 inches) long, measured from its wide end to its pointed tip. Sunflower seeds range from about 3 to 15 millimeters long, depending on the plant.

Size

Botanists call what people know as a sunflower seed an achene: a dry fruit that does not split open, with a thin, hard wall around a single true seed. The wall is the hull, and the true seed inside is the kernel that people eat. The Flora of North America, a standard guide to the continent's plants, gives the common sunflower's achenes as usually 4–5 millimeters long, and 3–15 millimeters at the extremes. Its description covers wild plants as well as crops.

Crop sunflowers come in two main types. Oilseed sunflowers usually have black seeds, with a thin hull that clings to the kernel. Their seeds are 38–50 percent oil. Confection sunflowers, grown for snacks and bird food, have larger seeds that are usually striped, with a thicker hull that comes off more easily. The striped seed in the explorer is the confection type. Confection sunflowers make up about 10 percent of all sunflower production.

Size comparisons

Nearly three seeds laid end to end would span a U.S. penny, which is 19 millimeters (0.75 inches) across.
A 7-millimeter seed is nearly twice as long as an ant 4 millimeters long.
A green coffee bean, about 9.6 millimeters long on average, is about 1.4 times as long as this seed.
A sunflower plant grows 1–3 meters (3–10 feet) tall, about 140 to 430 times the length of one of its seeds.

One flower head, hundreds of seeds

A sunflower's "flower" is really a head of many small flowers. The petals around the edge each belong to a ray flower. The center is packed with tiny disc flowers, from about 150 to more than 1,000 of them. Each disc flower can become one achene, so a single head can produce hundreds to more than a thousand seeds.

Wild sunflowers and early crop varieties needed insects to carry pollen between plants before they could set seed. Modern crop varieties can pollinate themselves, but they still benefit when bees and other insects visit.

A crop from North America

The Flora of North America calls the common sunflower the only native North American species to have become a major field crop. Ancient DNA shows that people domesticated it in eastern North America between 5,000 and 3,800 years ago.

Archaeologists sort ancient achenes by size: those 7 millimeters or longer are taken to come from domesticated plants. After domestication the seeds slowly grew larger. By about 1,000 years ago, in the river valleys of eastern North America's interior, they had reached the largest size seen before Europeans arrived.

Spanish explorers took sunflowers to Europe, and by 1580 they were a common garden flower in Spain. The crop was first grown on a large scale in Russia. Today sunflower kernels are the world's fourth-largest source of vegetable cooking oil.