In botany, a capsule is a type of simple, dry or (rarely) fleshy, fruit which splits open on maturity. They are produced by many species of flowering plants.

The capsule (Latin: capsula, small box) is derived from a compound (multicarpellary) ovary. A capsule is a structure composed of two or more carpels. In (flowering plants), the term locule (or cell) is used to refer to a chamber within the fruit. Depending on the number of locules in the ovary, fruit can be classified as uni-locular (unilocular), bi-locular, tri-locular or multi-locular. The number of locules present in a gynoecium may be equal to or less than the number of carpels. The locules contain the ovules or seeds and are separated by septa.

In most cases the capsule is dehiscent, i.e. at maturity, it splits apart (dehisces) to release the seeds within. A few capsules are indehiscent, for example those of Adansonia digitata, Alphitonia, and Merciera. Capsules are often classified into four types, depending on the type and location of dehiscence (see Simpson Fig 9.41 and Hickey & King ).

Loculicidal capsules possess longitudinal lines of dehiscence radially aligned with the locules, i.e. not at the septa, along the midrib or dorsal suture (seam) of the locules. If septa are absent, the dehiscence lines lie between the placentae. This type is common among many members of the Liliaceae such as Lilium (see illustration).

Septicidal capsules have dehiscence lines aligned with the sutures of the ovary septa or placentae, that is between the carpels.

Both loculicidal and septicidal capsules split into distinguishable segments called valves. The valves are a part of the pericarp (fruit wall) that has split away, without enclosing the seed or seeds. The borders of the valves may or may not coincide with the borders of carpels. These valves may remain attached to the fruit or fall off. In septicidal capsules the valves remain in place. In some capsules, the split occurs between carpels, and in others each carpel splits open.

Circumscissile capsules (pyxide, pyxis, pyxidium or lid capsule) have a transverse, rather than longitudinal, dehiscence line, so that the upper part of the capsule dehisces, usually forming a terminal lid (operculum) that opens (see illustration). An example is Plantago. A variant is the Septifragal capsule (valvular capsule) in which the outer walls break away from the septa and (usually axile) placentae as valves.

Poricidal capsules dehisce through pores (openings) in the capsule, as in Papaver, the seeds escaping through these pores.