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Fruit Terminology (Part 2)
Botany 115 Terminology
Fruit Terminology Part 2
C. Indehiscent Dry Fruits (Do Not Split Open At Maturity)
1. Achene: Small, one-seeded fruit; pericarp free from seed coat.
Note: In the grain or caryopsis, the pericarp is fused with the seed coat.
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The achene is the typical fruit of the sunflower family (Asteraceae). It is a small, one-seeded fruit containing a single seed. The seed is attached by a funiculus, but the seed coat is free from the inner wall of the pericarp.
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Achenes of the sunflower (Helianthus annuus). One achene has been sectioned to reveal the single seed inside. The seed is essentially free within the pericarp wall, except where it is attached at the placenta. Sunflower seeds of this variety with striped pericarps is used primarily for food. Seeds from achenes with solid black pericarps are used for sunflower oil.
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One-seeded achenes of buckwheat (Fagopyrum esculentum), an important crop plant native to central Asia. The three-sided achenes resemble miniature nuts from the beech tree (Fagus). This resemblance led to the German name "buchweizen" (beech-wheat) which became corrupted to the present name of buckwheat. The hulled achenes or groats are used in several brands of hot and cold breakfast cereals. The seeds are ground into flour which is used for pancakes, noodles and breads. In Russia, a nutritious porridge called "kasha" is made from buckwheat flour.
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Two angular nuts of American beech (Fagus grandifolia) within a spiny involucre. The three-sided nuts resemble the miniature one-seeded achenes of buckwheat (Fagopyrum esculentum). This resemblance led to the German name "buchweizen" (beech-wheat) which became corrupted to the present name of buckwheat.
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2. Anthocarp: Small, one-seeded fruit enclosed by a fused perianth or receptacle.
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In the four o'clock family (Nyctaginaceae), individual apetalous flowers have a tubular, petaloid calyx that resembles a sympetalous corolla. The lower portion of the calyx tightly enwraps the one-seeded achene and is persistent around the fruit as an anthocarp. The calyx base plus the enclosed seed-bearing achene is the unit of dispersal. In some members of the Nyctaginaceae, the persistent calyx base bears sticky glandular projections that aid in dispersal by adhering to the bodies of animals. This is especially true in pisonia trees (Pisonia umbellifera) in which the numerous glutinous anthocarps stick to the feathers of seabirds.
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Two anthocarps of the desert sand verbena (Abronia villosa var. villosa). Each
seed-bearing ovary (achene) is tightly encased within the persistent winged calyx.
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Left: Desert (dune) evening primrose (Oeothera deltoides ssp. deltoides). Right: Desert sand verbena (Abronia villosa var. villosa). Both species commonly occur together in sandy riverbeds of Anza-Borrego State Park, San Diego County.
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Yellow sand verbena (Abronia latifolia) on the coastal dunes of Monterey County.
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Yellow sand verbena (Abronia latifolia) on the coastal dunes of Monterey County.
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Two anthocarps of (Boerhavia intermedia) attached to the sticky stem of this small desert annual. Each elongate (obpyramidal), seed-bearing anthocarp is truncate at the widest end (apex). The anthocarp has five longitudinal ribs and is wrinkled (transversely rugulose) between the ribs. The minute anthocarps were photographed by Tom Chester in Palm Canyon, Anza-Borrego State Park (November 2003).
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3. Grain (Caryopsis): One-seeded fruit; pericarp fused with seed coat.
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Rice (Oryza sativa). A. Grain-bearing spikelet showing a pair of slender basal bracts (glumes) and the stalk (pedicel). The inflorescence is composed of numerous spikelets, each bearing a rice grain. B. An empty spikelet with the lemma and palea slightly separated from each other. These two leathery bracts enclosed the grain or caryopsis. C. A grain (caryopsis) removed from spikelet (B). The embryo or germ is at upper end. Beneath the brownish outer pericarp and seed coat layers (called the bran) is the endosperm tissue. Most of the vitamin B1 is found in the germ and bran portions, which are milled off in polished white rice.
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Grains of brown and polished white rice. In polished white rice (left), most of the bran and germ has been milled away, resulting in an improved flavor (at least to some people). The grains appear slightly more slender, with the apical germ region ground off giving the grains a slightly pointed appearance (red arrow). In white rice you are eating mostly the carbohydrate-rich endosperm tissue which lacks the vitamin B1 of the bran and germ. Even though it is less nutritious, white rice is still preferred by Asians, and is the most popular grain served in Chinese and Japanese restaurants in the United States.
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4. Samara: One-seeded, winged achene.
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The samara is a peculiar one-seeded fruit similar to an achene except the pericarp wall extends into a thin, papery wing. The above image shows two strikingly different samaras, one from the tree of heaven (Ailanthus altissima) and the other from big-leaf maple (Acer macrophyllum). The maple has a "double samara" composed of two seed-bearing pericarps, each with an elongate wing. The one-seeded fruits split apart and spin by autorotation as they fall to the ground. Some botanists refer to the maple fruit as a schizocarp because it splits into two indehiscent, seed-bearing sections.
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5. Nut: One-seeded fruit with hard pericarp.
A. Fagaceae: Oak (Quercus)
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The one-seeded nut of an acorn sits in a cup-shaped involucre composed of numerous overlapping scales. These acorns are from the cork oak (Quercus suber), the bark of which is the source of natural cork.
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B. Fagaceae: Chestnut (Castanea)
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The one-seeded nuts of the American chestnut (Castanea dentata) are produced in a spiny, cup-shaped involucre.
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C. Betulaceae: Hazelnut or Filbert (Corylus)
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The American filbert (Corylus americana) of the eastern United States produces a one-seeded nut enclosed in an involucre of leafy bracts. In the closely-related species of the Pacific northwestern United States (C. cornuta), the nut is produced in an elongate, tubular involucre.
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The beaked filbert (Corylus cornuta) of the Pacific United States produces a one-seeded nut within an elongate, tubular involucre. In this photo, the tubular involucre has been sectioned lengthwise (longitudinally) to expose the hard-shelled nut inside
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D. Juglandaceae: Pecan & Hickory (Carya)
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Note: Some botanists say that the husk of pecans and walnuts
contains tissue from the outer pericarp, and insist on referring
to these dry fruits as "drupaceous nuts" rather than true nuts.
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According to "The Morphology of the Flowers of the Juglandaceae" by W.E. Manning (1940), American Journal of Botany 27 (10): 839-852, the fruits of Juglans and Carya are drupe-like but not a drupe or dry drupe. The fruit is sometimes called a "tryma" but can be described as a nut. Webster's Third New International Dictionary describes a tryma as a nutlike drupe (as the fruit of the walnut or hickory) in which the epicarp and mesocarp separate as a somewhat fleshy or leathery rind from the hard 2-valved endocarp. The tryma is also defined as a drupe with a dehiscent husk, which fits the genus Carya perfectly.
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Pecan (Carya illinoensis): The green, fleshy outer husk or shuck splits into 4 valves, exposing a single large, one-seeded "nut." The husk is composed of leathery tissue derived (at least in part) from the fused sepals. The "tryma" is a fruit type defined as drupe with a dehiscent husk, which fits the pecan perfectly. The "hican" (C. x nussbaumeri) is a Carya hybrid resulting from a cross between the pecan (C. illinoensis) and the shellbark hickory (C. laciniosa).
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One-seeded "nuts" of the shellbark hickory (Carya laciniosa). The outer green husk has been removed. Each woody endocarp contains one seed with two conspicuous cotyledons resembling those of a pecan or a walnut. The shellbark hickory generally has larger nuts than the shagbark hickory (C. ovata). Both species of hickory are native to the deciduous forests of the northeastern United States, along with the mockernut (C. tomentosa), pignut (C. glabra) and bitternut (C. cordiformis).
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E. Juglandaceae: Walnut (Juglans)
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Black walnut (Juglans nigra), a deciduous hardwood tree native to the eastern and central United States. Some botanists refer to walnuts as nuts because the outer green husk contains involucral and calyx tissue, in addition to the outer pericarp. Unlike the closely-related pecan (Carya), the husk does not split into four sections and actually resembles the outer fleshy pericarp of a drupe. According to some botanical references, the outer green layer (husk) of the walnut is part of the pericarp and the hard shell surrounding the seed is the endocarp layer as in coconuts. In true nuts, the hard, indehiscent layer surrounding the seed is the ripened ovary wall or pericarp and the outer husk is composed of involucral tissue (or calyx tissue) that is not part of the ovary wall (pericarp). Depending on the reference, walnuts and pecans are referred to as true nuts or dry drupes. Some authors eloquently avoid this dilemma by calling these fruits drupe-like or "drupaceous nuts."
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An intricately-carved English walnut (Juglans regia).
Purchased from a vendor on the Great Wall of China.
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