Fruits

Fruit form or type can be an important consideration for identification, yet it can be difficult to interpret, especially for novice botanists. Fruits either open at maturity (dehiscent) to release seeds or they do not (indehiscent). Contaminants may be encountered as mature fruits or immature, whole fruits with or without seeds, fragments of fruits with or without seeds, or just seeds. Due to the variety of forms contaminants may take, the key does not focus on fruit type. However, it is worth keeping in mind, when comparing a specimen to the fruit types listed in a family fact sheet, that, for instance, an immature capsule may look similar to a dried berry. When possible, images of immature fruits are also included in the fact sheets.

Two indehiscent fruits (left) and two dehiscent fruits (right).
Two indehiscent fruits (left) and two dehiscent fruits (right).
Two species which, as contaminants, may be found as whole fruits, fruit segments, or partial fruits, or as seeds.
Two species which, as contaminants, may be found as whole fruits, fruit segments, or partial fruits, or as seeds.

As contaminants, fleshy, indehiscent fruits, such as berries or drupes, usually appear shriveled, often with a thin outer fruit wall and a dried fleshy inner wall. Berries are several- to many-seeded, while drupes have a stony pit(s) encasing a seed(s).

Illustration of berry in transection (top left) and berries whole and in longitudinal section.
Illustration of berry in transection (top left) and berries whole and in longitudinal section.
Top row: longitudinal sections of drupes, with drupe in middle showing pit open and seed exposed; bottom row: whole drupes.
Top row: longitudinal sections of drupes, with drupe in middle showing pit open and seed exposed; bottom row: whole drupes.

Most dry, indehiscent fruit types are single-seeded and are often difficult to distinguish from seeds. In fact, these fruits are often casually referred to as “seeds” or “seed units”. For these types of specimens, recognizing if they are seeds or single-seeded fruits, and then, what type of single-seeded fruit, will help in choosing between families. The presence of an easily removed fruit wall revealing the seed inside or accessory structures, such as persistent bracts, scales, tufts of hairs, or wings, may help distinguish fruits from seeds. Even though wings and hairs occur on seeds, they are more frequently found on fruits, since accessory structures usually develop from floral parts. The easiest to recognize (and most common) accessory structures are persistent sepals (calyx) or petals (corolla) or both (perianth). Sometimes, persistent perianths can be strongly adherent, as in the case of some Polygonaceae fruits. Inspecting a specimen under 10x to 20x magnification will assist in determining if it has accessory structures.

Single-seeded fruit with persistent perianth (upper left); same fruit with removed perianth, fruit wall split open, and extracted seed.
Single-seeded fruit with persistent perianth (upper left); same fruit with removed perianth, fruit wall split open, and extracted seed.
Single-seeded fruits with accessory structures, clockwise from upper left: persistent style; winged fruit wall; persistent winged perianth attached to fruit and fruit removed from perianth; two examples of persistent perianths.
Single-seeded fruits with accessory structures, clockwise from upper left: persistent style; winged fruit wall; persistent winged perianth attached to fruit and fruit removed from perianth; two examples of persistent perianths.

Some of the most commonly intercepted dry, single-seeded, indehiscent fruits are grains (or caryopses). This fruit type only occurs in the grass family (Poaceae). The fruit wall is thin and usually completely fused to the seed coat. Poaceae fruits are often dispersed within highly modified bracts as a single unit (floret) or as multiple units (florets or spikelet). Distinguishing the fruit from the seed is not necessarily needed to identify this family, but a familiarity with the dispersal units of grasses will help. If the fruit-seed is dissected, the shape and position of the embryo is fairly unique to this family.

Caryopses with hilum, embryo, and scutellum indicated.
Caryopses with hilum, embryo, and scutellum indicated.
Typical grass inflorescence showing parts of spikelets and florets.
Typical grass inflorescence showing parts of spikelets and florets.
Leptochloa viscida spikelet, floret, and caryopsis, clockwise from upper left: immature spikelet with five florets and three empty glumes in lateral view; florets in dorsal view showing lemma; floret in ventral view showing palea and edges of lemma; caryopsis in dorsal view and in ventral view (inset).
Leptochloa viscida spikelet, floret, and caryopsis, clockwise from upper left: immature spikelet with five florets and three empty glumes in lateral view; florets in dorsal view showing lemma; floret in ventral view showing palea and edges of lemma; caryopsis in dorsal view and in ventral view (inset).

The other single-seeded, indehiscent fruit types are distinguished based on differences in the thickness and adherence of the fruit wall to the seed (achene, nut, and utricle) and if winged (samara) or not. Achenes are found in about 30 families; of these, Asteraceae is the most likely to be intercepted.

Single-seeded fruit types.
Single-seeded fruit types.
Asteraceae achenes with persistent pappus (calyx).
Asteraceae achenes with persistent pappus (calyx).

Dehiscent fruits open upon maturity to release seeds . Capsules or follicles are common dehiscent fruit types, which are typically dry (rarely fleshy) and multi-seeded. Whole or fragments of mature or immature dehiscent fruits may be found with or without the seeds in potpourri, decorative plant arrangements, and handicraft items.

Capsules at maturity.
Capsules at maturity.
Dehiscent fruit types (without their seeds) that are imported as dried botanicals.
Dehiscent fruit types (without their seeds) that are imported as dried botanicals.
About fruits and seeds