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Fruit Terminology (Part 1)
Botany 115 Terminology
Fruit Terminology Part 1
A. General Fruit Terminology
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Carpel: Leaf-like megasporophyll bearing one or more ovules on the inner surface. In dehiscent dry fruits that split open, carpels are represented by the seed-bearing sections. Carpels are difficult to distinguish in dry, indehiscent fruits (e.g. nuts) and fleshy fruits (e.g. berries). Carpels are the innermost parts of a complete flower and they are united to form the gynoecium (pistil).
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B. Dehiscent Dry Fruits (Split Open At Maturity)
1. Legume or Pod: Composed of one carpel.
Note: Some legumes are indehiscent and do not split open.
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A legume (such as a bean pod) is composed a one folded carpel. It splits lengthwise along two seams into two sections, each of which represents half of a carpel. Some legume pods, such as carob and mesquite, are indehiscent and do not split open.
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The peanut (Arachis hypogea) is a dehiscent legume that is harvested from below the soil. The legume was originally formed above ground following pollination. After fertilization, the flower stalk of the peanut curves downward, and the developing pod is forced into the ground by the proliferation and elongation of cells under the ovary. The pod typically contains two seeds, each with a papery seed coat. Peanut seeds are eaten raw, salted and roasted. Peanuts are ground into peanut butter and Thai peanut sauce, and the expressed oil is used in cooking. Peanuts are also used in cookies, peanut brittle and candy bars.
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Note: Some legume fruits are indehiscent, including the carob tree, mesquite and honey locust. In addition, some legume fruits are oblong, rounded, kidney-shaped (reniform), or coiled (spiral-shaped), such as sweet clover (Melilotus alba and M. officinalis), black medic (Medicago lupulina), bur clover (M. polymorpha) and alfalfa (M. sativa). Some specialized legume fruits (called loments) break apart into indehiscent, seed-bearing segments. A good example of a loment is the fruit of crown vetch (Coronilla varia), a European wildflower that is naturalized throughout parts of North America. The slender pods are constricted between the seed-bearing segments.
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Crown vetch (Coronilla varia) from Palomar Mountain in San Diego County, California. Note the slender legume fruit (called a loment) with constrictions between the seed-bearing segments. The fruit breaks apart transversely into seed-bearing sections. This attractive European wildflower has become a troublesome weed in parts of North America. It has been planted on road cuts for erosion control, but is a very invasive perennial with creeping rhizomes and prolific seed production.
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Stick-tights or beggar's-ticks (Desmodium cuspidatum) produces slender loments that break into small, one-seeded joints covered with tiny barbed hairs. The individual joints are so flat that they are exceedingly difficult to remove from your socks. Like little flat ticks, you must individually pull off each one. This can be exasperating when your socks are covered with them. Several species of this remarkable hitchhiking herb are native to the midwestern and eastern United States.
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2. Capsule: Composed of several fused carpels.
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The separate carpels of a true capsule were originally fused together to form the pistil or gynoecium. They separate along the septa or along the locules between septa.
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Four methods of dehiscence in capsules: The carpels may separate along the septa or along the locules between the septa. Some capsules dehisce by a lid that falls off exposing the seeds. Poppies of the genus Papaver, including the opium poppy (P. somniferum), dehisce by small apical pores near the top of the capsule. As the capsule moves back and forth in the wind, the seeds are released like a pepper shaker.
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It sould be noted here that some capsules are indehiscent. Their carpels do not separate and release the seeds. Two examples of plants with indehiscent capsules are the South African baobab tree (Adansonia digitata) and two species of South African gardenias (Gardenia thunbergii and G. volkensii). The seed pods of South African gardenias are chewed opened by large herbivores, and the seeds are dispersed in their feces.
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Indehiscent capsule of the baobab tree (Adansonia digitata). Left: A dry fruit showing the velvety outer exocarp. Right: Longitudinal section of a dry fruit showing the large, angular seeds. Each seed is embedded in a white pulp which has a pleasant tart flavor. The lower left seed has been removed from the pulp. The common names of "cream-of-tarter tree" and "lemonade tree" are derivied from the powdered pulp which is mixed which water to make a refreshing drink. Baboons tear open the fruits to eat this tasty pulp.
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3. Follicle: One carpel that splits along one seam.
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The single carpel of a follicle splits open along one seam. When completely opened, the carpel resembles a thick, dried leaf. It is easy to see that the single carpel of a follicle is a modified, seed-bearing leaf (megasporophyll).
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4. Silique: Two carpels separated by a seed-bearing septum.
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The silique is an elongate fruit composed of two carpels separated by a seed-bearing partition. The silicle is very similar except it is much shorter (less than twice as long as broad). Siliques and silicles have parietal placentation. They are the characteristic fruits of the mustard family (Brassicaceae). Some members of the mustard family have siliques that do not split longitudinally into two separate carpels. For example, fruits of the radish (Raphanus sativus) split transversely into seed-bearing sections (joints).
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The overlapping seeds of bitter cress (Cardamine) are connected to alternate edges of the septum within each locule. The minute seeds are attached to both margins of the central septum. This revelation requires the skillful use of a dissecting microscope. In the Jepson Flora of California (1993), this genus keys out under "one row of seeds in each locule," without mentioning the alternating seed attachments along both edges of the septum. Apparently, the superficial appearance of the overlapping seeds in a single file is the defining character for the key.
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A species of bitter cress (Cardamine) collected along the damp seepage area of a lawn in northern San Diego County. It is an annual with a fibrous root system (without rhizomes). The leafy stems are erect or ascending (curving upward from the base). The leaves are odd pinnate with 2 or three pairs of leaflets. This species of bitter cress greatly resembles the European annual C. flexuosa With. Another native species reported for San Diego County (C. oligosperma Torrey & A. Gray) has similar compound leaves; however, it has a distinct basal leaf rosette that is lacking in this species. It is interesting to note that C. flexuosa With. has now been added to the San Diego Natural History Museum on-line Checklist of Vascular Plants of San Diego County.
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The seeds of water cress (Rorippa nasturtium-aquaticum) are connected along both margins of the septum within each locule. In the Jepson Flora of California (1993), this species keys out under "two rows of seeds in each locule." Although Cardamine also has seeds attached in two rows, the seeds are overlapping and do not appear distinctly 2-ranked. In Rorippa the seeds appear more distinctly two-ranked, and this is apparently a defining character for the key.
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Inflorescence (raceme) of shepherd's-purse (Capsella bursa-pastoris), a common European annual that is naturalized in southern California. The silicles are inverted heart-shaped (obcordate). The membranous partitions remain on the pedicels long after the valves of the silicles have fallen away.
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Moonwort (Lunaria annua), a European annual or biennial naturalized in California. The fruits of this species are called silicles because they are broad compared with the elongate and slender siliques. Generally silicles are only twice as long as broad (or less). The septum of each silicle remains attached to the dried flower stalk, long after the valves and seeds have fallen away.
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Go To The Diversity Of Flowering Plants