Dry indehiscent fruits

Dry indehiscent fruits include the caryopsis, the achene, the samara, and the "nut".

A caryopsis is an indehiscent fruit in which the seed coat is completely fused to the fruit wall. This fruit type is characteristic of the grass family and is commonly called a grain. A grain (caryopsis) is technically a one-seeded fruit, but you can't get the seed out of the fruit because they are fused together.

Caryopsis of maize
The fruit of maize (corn) is a caryopsis. Each grain or kernel is a fruit that has developed from the ovary of a separate pistil. The micrograph (stained) shows the fused fruit wall and seed coat, with the rest of the seed inside (endosperm staining blue-purple, embryo staining pink; micrograph by Alejandro Clark)

An achene is an indehiscent fruit in which the seed coat is NOT fused to the fruit wall. An example is the sunflower "seed": the shell of the sunflower "seed" is actually the fruit wall.

Achene
Achene of sunflower

A samara is a winged fruit. (Seeds of some species may be winged, but samaras are winged fruits; they each contain a single seed.)

Samaras
Samaras of various species. [Drawings from Groom 1898 and Rusby 1911]

Some indehiscent fruits with very hard pericarps are called "nuts" (not shown).

A schizocarp is a fruit that separates into (usually) single-seeded segments at maturity. The schizocarp develops from the ovary of a single pistil with multiple, fused carpels. At maturity, however, fruit sections derived from different carpels separate from each other. These fruit sections are called mericarps. They are considered indehiscent because, although the fruit splits up, the fruit sections do not split open to release their seeds. Some members of the Malvaceae (the hibiscus family) and the Geraniaceae (the geranium family) have schizocarps.

Schizocarps
Schizocarps of the Malvaceae and Geraniaceae. Each is from the ovary of a single pistil (note the single style on each). The wedge-shaped one-seeded segments in the Malvaceae and the beaked one-seeded segments in the Geraniaceae are called mericarps. [Drawings from Groom 1898]

In a somewhat similar manner, lobes of deeply lobed ovaries may separate at maturity, with each lobe containing a single seed. These single-seeded structures are called nutlets. They are not considered schizocarps because the lobes on the ovaries (which become nutlets) do not represent separate carpels.

Nutlets
Deeply lobed ovary that will separate into nutlets at maturity. [Adapted from Groom 1898 and Rusby 1911]

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