Achene

Achenes are small, one-seeded dry fruits that do not open to release the seed, which means they are indehiscent.

​[Pronounced ah-KEEN or eh-KEEN, depending on who you ask.]

Examples of achenes
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The tiny bits that you see on the outside of a strawberry are achenes. If you look closely, you will see that each tiny bit is actually a dried fruit that contains a single seed. If those seeds happen to sprout while still attach to the strawberry, it is called vivipary.

Strawberry achenes (Rich Caulton)

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Many members of the sunflower family feature achenes. Cardoons, cannabis, caraway, and roses also produce achenes. Some plants, such as the maple tree, produce modified achenes, called samaras. Other plants, such as wheat, barley, and other grains, produce a caryopsis, which is much like an achene, except that the seed coat is stuck to the pericarp. In the same way, each spike of a dandelion is a type of achene known as cypselae. 

Dandelion cypselae (Wikipedia)

Cypsela of cardoon (Penarc)

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Scientists are still sorting out the details of this particular mode of seed life. Until recently, the individual seeds from sunflowers were considered achenes, but genetic research may be changing that decision. I’ll keep you posted.