Structure and Formation Of Dehiscent and Indehiscent Dry Fruits

The Achene: Indehiscent dry fruits resulting from a single carpel enclosing a single seed. In some cases a receptacle may bear a collection of achenes resulting from an apocarpous gynaecium. Such a collection may be regarded as a compound fruit and is described as an etaerio of head of achenes, e.g., buttercup, avens, Clematis, Anemone. Species cases of achenes are:

The Nut: Pericarp distinctly hard and woody, e.g., hazel, oak, dock, rhubarb, buckwheat, sweet chestnut, beech.

(Note: The acorn is derived from a trilocular ovary with two ovules in each loculus, but almost invariably only one seed in one of the carpels reaches maturity.)

The Caryopsis: Pericarp inseparably fused to the seed coat, e.g., grains of cereals and grasses.

The Samara: Pericarp produced into a wing, e.g., ash, elm.

The Cypsela: Ultimately a one – seeded indehiscent dry fruit but originating in a bicarpellary ovary. Part of the wall is receptacular tissue, although this is not differentiated from the true pericarp and the wall appears as a single layer. It could be regarded as a false fruit and is characteristic of the family compositae, e.g., sunflower

The Follicle: Dehiscent dry fruits formed from a single carpel bearing one or more seeds and splitting along one suture (ventral) only.

In many cases a head of follicles is formed from an apocarpous pistil, e.g., Delphinium, Aquilegia, monkshood, marsh marigold, paeony, Magnolia, hellebore.

The Legume: Dehiscent dry fruits formed from a single carpel bearing one or more seeds and splitting along both dorsal and ventral sutures, e.g., gorse, broom, pea, bean, laburnum, Lucerne, lupin, vetch, clover and others of the family Papilionaceae.

Fruits With Special Encapsulation

The Lomentum: A pod or legume transversely divided by false septa into separate compartments each bearing one seed, e.g., Cassia, Acacia. Note that siliquas may be classed as loments when transversely divided into one – seeded parts.

The Capsule: A dehiscent dry fruit formed from a syncarpous gynaecium, the carpels of which open by slits, pores or teeth, e.g., horse chestnut, Antirrhinum, poppy, Lychnis, Dianthus, foxglove, pimpernel, violet, iris.

Special cases:

The Silicula: A capsule formed from a bicarpellary ovary separated into two loculi by a false septum: broader than long, e.g., shepherd’s purse, honestly.

The Siliqua: As above but longer than broad, e.g., wallflower, cabbage. Both these types (a) and (b) are peculiar to the family Cruciferae.

The Carcerulus: A capsule modified by constriction or branching of carpels to form a number of one – seeded segments or nutlets into which the fruit finally splits, e.g., dead nettle and other labiates.

The Regma: Similar to the carcerulus but the separation into segments is explosive and the segments themselves may dehisce, e.g., Geranium.

The Schizocarp: A dry fruit formed from a synearpous gynaecium in which the carpels separate from one another as one-seeded mericarps. E.g., hollyhock, mallow.

Special cases:

The Double Samara: Composed of two or more winged indehiscent carpels which separate before or after wind dispersal, e.g., sycamore, maple.

The Cremocarp: Bicarpellary, bilocular fruit in which the two carpels separate into one – seeded indehiscent mericarps which remain attached for a time to a central supporting strand, the carpophores, before dispersal, e.g., hogweed, parsnip, caraway and others of the family Umbelliferae.

(Note: the carcerulus and regma are sometimes considered as schizocarpic fruits.)

Succulent Fruits

The Drupe: A fleshy fruit formed from a monocarpellary or syncarpous gynaecium, containing one or more seeds each of which is enclosed by a hard, stony portion of the pericarp at dispersal. The dispersal structure may be a single one – seeded “stone” as in the plum, or in several distinct portions as in the holy, elder and ivy. The inner hard portion of the pericarp which surrounds the seed is called the endocarp. The middle region of the pericarp, the mesocarp, is soft and succulent and this is covered externally by a skin – like epicarp. Examples of drupes are cherry, almond, walnut, coconut, elder. In many cases the receptacle bears a collection of small drupes, drupels or drupelets resulting from an apocarpous gynaecium, e.g., blackberry, raspberry.

The Berry: A fleshy fruit formed from a monocarpellary or syncarpous ovary containing one or more seeds each of which is surrounded only by its own hardened seed coat at dispersal. There is no hardened endocarp in the pericarp, e.g., currant, gooseberry, marrow, orange, lemon, cucumber, banana, tomato, grape, date.