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A caryopsis is a dry, one-seeded fruit that remains closed at maturity and has its pericarp fused to the seed coat. It is characteristic of grasses. A maize kernel is therefore a whole fruit, even though everyday language often calls it a seed.^[ref]

The developmental distinction survives the fusion: the pericarp comes from the ovary wall, whereas the seed coat comes from the coverings of the ovule. A close attachment between the two does not make them the same tissue.

The exocarp is the outermost region of the pericarp. It forms the external covering of the fruit wall, outside the mesocarp and endocarp. The skin of a peach illustrates the term.^[ref]

The exocarp belongs to the fruit, whereas the seed coat belongs to the enclosed seed. They may both act as protective coverings, but function alone does not make them the same structure. In a caryopsis their close attachment can conceal the distinction; tracing their origins to ovary and ovule respectively preserves it.

An indehiscent fruit remains closed at maturity instead of splitting open in a regular way to release its seeds. The category describes the opening behaviour of the fruit, rather than the number of seeds or the origin of its floral tissues.^[ref]

An achene and a caryopsis are illuminating examples. Both remain closed, but their internal construction differs: in an achene, the seed is free from the pericarp; in a caryopsis, the pericarp and seed coat are fused. Thus knowing that a fruit is indehiscent does not identify its precise fruit type.^[ref]

Closed does not mean permanently sealed against every later event. A fruit may eventually decay or be broken by an animal. The distinction from a dehiscent fruit concerns its normal opening at maturity, not whether a person can cut it open or its seed can eventually emerge during germination.

Maize is the domesticated grass Zea mays, grown for its grain. A maize kernel is a caryopsis: a fruit in which the enclosing wall is closely attached to the seed. The male flowers form the tassel, while female flowers occur in ears; wind carries pollen between them. Having both kinds of flowers on one plant is different from having separate male and female plants.

Its domestication from teosinte provides a concrete example of how changes in developmental regulation alter a crop. Research on apical dominance identified the teosinte branched1 gene as a major contributor to the suppression of side branches in maize. Comparing gene activity and mutant plants connected a conspicuous architectural difference to regulation of axillary growth.^[ref]

The pericarp is the wall of a fruit, derived from the wall of the ovary. Its regions can be distinguished as outer exocarp, middle mesocarp and inner endocarp.^[ref]

These regions need not have the same texture: in a drupe, such as a peach, the fleshy middle surrounds a hard inner stone. The stone is hardened pericarp; the seed lies inside it. In a caryopsis, by contrast, the pericarp is closely fused to the seed coat. These examples explain why a fruit's protective covering should be identified by its developmental origin as well as its appearance.

A grass is a flowering plant in the family Poaceae, which includes maize, rice, wheat and bamboos. Typical grass leaves have a sheath clasping a jointed plant stem and a blade extending away from it; a ligule often occurs at their junction. The flowers are grouped into spikelets, and the characteristic fruit is a caryopsis.^[ref]

Recognizing the family requires more than seeing narrow green leaves. Many grass stems have hollow intervals between solid joints, but maize has substantial internal tissue and bamboos can be woody. Shared floral organization provides a more reliable basis for comparison than one vegetative feature. Grass biology connects the structure of a lawn to the grain crops that feed people.