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Flowers
For a general discussion of the structure and function of the flower, see Plant Reproduction
Flower Parts [Illustration]
The following are the major flower parts:
- Androecium: The male parts of the flower forming a whorl between the gynoecium (the female parts) to the inside and the corolla (the showy parts) to the outside. It includes one to many stamens, each of which typically includes a filament and an anther. Within the anther pollen is produced.
- Anther: The part of a stamen where pollen is produced. It typically sits atop a filament.
- Calyx: The outermost whorl of modified leaves found in the typical flower. It is the collective term for all the sepals of a single flower and is frequently green and inconspicuous.
- Corolla: The usually showy part of the flower, a whorl of modified leaves just inside the calyx. This is the collective term for all the petals of a single flower.
- Carpel: The structure that bears and encloses the ovules (egg-containing structures in the ovary).
- Corona: An extra-floral set of appendages that protrude from between the corolla and the stamens or from the corolla. The crown-like corona of Daffodils is an example.
- Filament: The part of the stamen that typically serves as a stalk for the anther.
- Fruit: A mature ovary that frequently contains mature ovules or seeds.
- Gynoecium: The female parts forming a whorl at the center of the flower. It includes one to many pistils, each of which typically includes a stigma, style, and ovary.
- Hypanthium: The cup formed from the receptacle and/or perianth that has fused with the androecium. Not all flowers have a hypanthium. The rose family (Rosaceae) has many species whose flowers have a hypanthium.
- Ovary: The typically enlarged, bottom part of the pistil where ovules are produced.
- Ovule: The egg-containing structures within the ovary that develop into seeds.
- Locule: A chamber within the ovary. A simple ovary has a single locule while a compound ovary has more than one locule. For example, a bicarpellate ovary has two locules. The number of locules is usually the same as the number of carpels.
- Pedicel: The "stalk" that supports a single flower in an inflorescence made up of more than one flower.
- Peduncle: The "stalk" that supports either a single flower, in plants that produce only a single flower, or an entire inflorescence.
- Perianth: The collective term for all the sepals and petals of a single flower.
- Petal: A sterile, highly modified leaf that is a single "unit" of the corolla. Petals are usually the showy part of a flower and may include special structures, called nectaries, for attracting insect pollinators and/or special, ultraviolet markings, called honey guides, for guiding insects, such as bees, to pollen.
- Pistil: A single female reproductive "unit." The pistil typically has three recognizable regions: the stigma, the style, and the ovary.
- Pollen: The male gametophyte. Pollen grains give rise to sperm.
- Rachis: The central stalk of an inflorescence to which the pedicels of individual flowers are attached.
- Receptacle: The region at the top of either the peduncle or pedicel where the floral appendages (for example, sepals, petals, stamens, and pistils) are attached.
- Sepal: A sterile, modified leaf that is a single "unit" of the calyx. Sepals are frequently green and inconspicuous.
- Stamen: The male reproductive structure made up of an anther and a filament.
- Staminode: A whorl of modified leaves just outside the stamens. Staminodes are frequently inconspicuous and stamen-like.
- Stigma: Typically, the top portion of a pistil, which receives pollen and provides conditions necessary for their germination.
- Style: The typically elongated region of a pistil between the stigma and ovary.
- Tepal: The term used for any single "unit" of the perianth when sepals and petals are morphologically similar.
Botanists often rely on reproductive characteristics to classify plants and establish their evolutionary relationships. Because the flower is the structure where reproduction occurs, there is a large body of terminology describing flowers in minute detail. Some of these terms are presented here. Becoming familiar with these terms not only can help you identify plants but also develop a greater understanding of their relationships.
Flower Sexuality
- Bisexual: With both stamens (male parts) and pistils (female parts).
- Pistillate: Female flowers-that is, imperfect flowers lacking stamens.
- Staminate: Male flowers, that is, imperfect flowers lacking pistils.
Plant Sexuality
- Dioecious: Species having male and female plants (that is, only male flowers on some plants and only female flowers on different plants).
- Monoecious: Species having both sexes on the same plant in separate (that is, imperfect) flowers.
- Polygamous: Species having both imperfect (pistillate and/or staminate) flowers and perfect flowers on the same plants.
- Polygamo-dioecious: Polygamous, but primarily dioecious.
- Polygamo-monoecious: Polygamous, but primarily monoecious.
Numbers of Flower Parts
- Complete: Flowers that have all four floral whorls (calyx, corolla, stamens, and pistils).
- Incomplete: Flowers that lack one or more of the four floral whorls (calyx, corolla, stamens, or pistils).
- Perfect: Flowers with both stamens (male parts) and pistils (female parts).
- Imperfect: Flowers lacking either stamens (male parts) or pistils (female parts).
Position of Flower Parts [Illustration]
- Epigynous: The perianth (sepals and petals) and androecium (male parts) are attached above the base of the ovary. Therefore, the ovary is inferior or half-inferior.
- Half-inferior: The ovary is surrounded by, or embedded in, the receptacle (the region at the top of either the peduncle or pedicel where floral appendages are attached). Therefore, the flower is epigynous.
- Hypogynous: The perianth (sepals and petals) and androecium (male parts) are attached below the ovary. Therefore, the ovary is superior.
- Inferior: The ovary sits primarily below the attachment point of the perianth (sepals and petals) and androecium (male parts). Therefore, the perianth is epigynous.
- Perigynous: The perianth (sepals and petals) and androecium (male parts) are fused at the base so that the sepals, petals, and stamens appear to arise from the rim of a floral cup (the hypanthium). This condition is frequently found in plants of the rose family (Rosaceae).
- Superior: The ovary sits primarily above the attachment point of the perianth (sepals and petals) and androecium (male parts). Therefore, the perianth is hypogynous.
Perianth Terminology [Illustration]
The perianth is the collective term for all the sepals and petals of a single flower.
- Apetalous: A flower lacking petals. Common in wind-pollinated plants.
- Banner: Topmost petal of the flowers of some plants in the pea family.
- Beard: A sepal or petal with a dense cluster or line of hairs.
- Claw: A very narrow, stalk-like base of a sepal or petal.
- Cruciform: A corolla that, when viewed from above, appears cross-shaped.
- Keel: The two united lowermost petals of the flowers of some plants in the pea family.
- Lobe: Any distinct segment of a divided sepal or petal. Members of the pink family (Caryophyllaceae) have divided petals that appear to have been cut with pinking shears (thus the common family name, pink).
- Spur: Any hollow protuberance from a sepal or petal. Impatiens species, for example, frequently have spurred sepals.
- Wing: One of two lateral petals of the flower of some plants in the pea family.
Corolla Parts
Corolla is the collective term for all the petals of a single flower. This is usually the showy part of the flower.
- Limb: In fused corollas, any extension of the petal beyond its fused base. Members of the phlox family (Polemoniaceae) have lobes that are extensions of the corolla tube.
- Throat: The opening at the top of the tube in fused corollas.
- Tube: The tube-like structure where the petals are united at the bottom of fused corollas.
Corolla Shapes [Illustration]
Corollas can be either actinomorphic (radially symmetrical, meaning that when you look down on the calyx or corolla you can see an infinite number of bisecting lines or planes that can cut the flower in equal halves) or zygomorphic (bilaterally symmetrical, meaning that when you look down on the calyx or corolla you can see that only one bisecting line that can cut the flower in equal halves). The following are different actinomorphic forms:
- Campanulate: Bell-shaped, as in bellflowers (Campanula species).
- Funnelform: Funnel-shaped, as in bindweeds (Convolvulus species).
- Rotate: Wheel-shaped, as in bluets (Hedyotis caerulea).
- Salverform: Trumpet-shaped, as in Russian olive (Elaeagnus angustifolia).
- Tubular: Cylindrical, as in trumpet vine (Campsis radicans).
- Urceolate: Urn-shaped, as in highbush blueberry (Vaccinium corymbosum).
The following are different zygomorphic forms:
- Bilabiate: With two lips composed of fused petals, as in snapdragon (Antirrhinum majus).
- Galeate: With a helmet-shaped appendage on one side. The corollas of monkshoods (Aconitum species) are galeate.
- Saccate: With an enlarged, pouch-like appendage on one side, as in the lady-slipper orchid (Cypripedium acaule).