[Biology Class Notes] on Achene Pdf

Achene or the achene fruit is a dry and one-seeded fruit lacking special seams, which split to release the seed. As in buckwheat, the seed coat is attached to the thin and dry ovary wall (or husk) by a short stalk, allowing the seed to be easily removed from the husk. The fruits of several plants present in the buttercup family and the rose family are the achenes.

About Achene

An achene is a fruit when defined botanically. It is derived from the ovary wall that is what defines a fruit. It has only one embryo (called a seed). When mature, it does not open, but rather the developing seed breaks it apart when the germination takes place. The achene’s thin wall is not fused with the seed that it encloses, in contrast to the fruits of grasses, otherwise, which resemble achenes. The fruit of grass is known as a grain of caryopsis.

The fact that achene is not fleshy like a plum does not alter the fact that it is a fruit, to speak botanically.

This has much to do with the difference between what we “sensibly” refer to like fruit and what a fruit anatomically consists of, from the botanist perspective. We think of strawberries as a fruit, but that thing we like to is has derived from the calyx of the flower, but not the ovary’s wall. The tiny brown structures present on the surface of the strawberry are hundreds of achenes, each enclosing a single seed. Each of these seeds develops from a single ovary, and the wall of that ovary develops into the hardened and thin covering, which is achene. In the same way, the fruits of roses are not the “hips” (or hypanthium), which consist of calyx tissue, but rather the achenes found within the hypanthium.

Examples

The fruits of buckwheat, buttercup, quinoa, caraway, cannabis and amaranth are a few typical achenes.

Sometimes, the achenes of the strawberry are mistaken for seeds. Strawberry is an accessory fruit with an aggregate of achenes on its outside surface, and what is eaten is the accessory tissue.

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An expanded hypanthium (or aka floral tube) is a structure in which the basal portions of the corolla, the calyx, and the stamens join with the rectangle to form a cup-shaped tube, which is encased within an expanded hypanthium (or aka floral tube).

Variations

A winged achene, as in maple, is known as a samara.

Some of the achenes have accessory hair-like structures, which cause them to tumble in the wind in a manner similar to the tumbleweed. Sometimes, this type is known as a diaspore or tumble fruit. Anemone virginiana is an example.

A grain, also known as a caryopsis, is a type of fruit that resembles an achene but differs in that the pericarp is fused to the grain’s thin seed coat.

A utricle is similar to achene, but the fruit is inflated or is bladder-like.

Sometimes, the fruits of the sedges are considered achenes, although their one-locule ovary is given as a compound ovary.

While it comes from the inferior compound ovary, the fruit of the Asteraceae family is very similar to achene, which is sometimes mistaken for one (having one locule). A special term for the Asteraceae fruit is given as cypsela (which is cypselas or plural cypselae or the community achene). For example, the white-grey husks of the sunflower achene seed are the cypsela fruit walls. Several cypselus (for example, dandelion) contain calyx tissue attached that functions in the biological dispersal of the seed.

Bur-oak Acorns

Acorn is similar to achene, but the pericarp (or the ovary wall) is papery-thin and adherent to the seed tightly. We cannot crack open a corn kernel and remove the seed the way we can with sunflower achene. The coat can be milled off, as when the white rice is manufactured by brown rice processing. The grain is given as a fruit in one family only, but what a family! The grass family (which is the Poaceae) is most important because the grasses are primary components of several ecosystems, and grass fruit forms the basis of specifically all the agricultural economies, as corn, rice, oats, barley, millet, and wheat.

What Does a Seed Contain?

An embryo is a handful of plant cells that, when they start to divide and grow, creates a root and shoot. At times, it is called a Zygote.

A food reserve, usually called starch, will supply energy to the developing embryo once germination starts and prior to the root is established. The zygote and the food reserve together form the Endosperm.

A hard protective shell of some sort, which is sufficiently porous to allow the water in to dampen the starch and start the process of growth. This can be the Endosperm’s outer layer, or a residual of the flowering tissue of the parent plant, or both.

Aromatic compounds are intended to protect the seed by preventing it from being eaten.