Theme.
MORPHOLOGY OF THE REPRODUCTIVE ORGANS OF PLANTS
The reproductive structures are more varied than vegetative, and are usually specific to a particular group of plants, such as flowers and seeds, fern sori, and moss capsules. Structures such as flowers and fruits are only found in the Angiosperms divisions.
FLOWER is the total reproductive structure of an Angiosperm. Its basic parts include the peduncle, receptacle, sepal, petal, stamens and carpels (pistils).
Flowers may be: 1. Unisexual or bisexual (monoecious or dioecious);
2. Symmetry of flower: actinomorphic or zygomorphic;
3. Calyx: with separate or attachment sepals, number of sepals;
4. Corolla: with separate or attachment petals, number of petals;
5. Type of androecium: number of stamens, their shape and ar-
rangment;
6. Type of gynoecium: number of pistils, their arrangment;
ovary position (superior or inferior);
7. Compose flower formula
Flower specialization and pollination
Each flower has a specific design which best encourages the transfer of its pollen. Cleistogamous flowers are self pollinated, after which, they may or may not open. Many Viola and some Salvia species are known to have these types of flowers.
Entomophilous flowers attract and use insects, bats, birds or other animals to transfer pollen from one flower to the next. Flowers commonly have glands called nectaries on their various parts that attract these animals. Some flowers have patterns, called nectar guides, that show pollinators where to look for nectar. Flowers also attract pollinators by scent and color. Still other flowers use mimicry to attract pollinators. Some species of orchids, for example, produce flowers resembling female bees in color, shape, and scent. Flowers are also specialized in shape and have an arrangement of the stamens that ensures that pollen grains are transferred to the bodies of the pollinator when it lands in search of its attractant (such as nectar, pollen, or a mate). In pursuing this attractant from many flowers of the same species, the pollinator transfers pollen to the stigmas—arranged with equally pointed precision—of all of the flowers it visits.
Anemophilous flowers use the wind to move pollen from one flower to the next, examples include the grasses, Birch trees, Ragweed and Maples. They have no need to attract pollinators and therefore tend not to be “showy” flowers. Male and female reproductive organs are generally found in separate flowers, the male flowers having a number of long filaments terminating in exposed stamens, and the female flowers having long, feather-like stigmas. Whereas the pollen of entomophilous flowers tends to be large-grained, sticky, and rich in protein (another “reward” for pollinators), anemophilous flower pollen is usually small-grained, very light, and of little nutritional value to insects.
Flowering plants are heterosporangiate, producing two types of reproductive spores. The pollen (male spores) and ovules (female spores) are produced in different organs, but the typical flower is a bisporangiate strobilus in that it contains both organs.
A flower is regarded as a modified stem with shortened internodes and bearing, at its nodes, structures that may be highly modified leaves.[1] In essence, a flower structure forms on a modified shoot or axis with an apical meristem that does not grow continuously (growth is determinate). Flowers may be attached to the plant in a few ways. If the flower has no stem but forms in the axil of a leaf, it is called sessile. When one flower is produced, the stem holding the flower is called a peduncle. If the peduncle ends with groups of flowers, each stem that holds a flower is called a pedicel. The flowering stem forms a terminal end which is called the torus or receptacle. The parts of a flower are arranged in whorls on the torus.
The four main parts or whorls (starting from the base of the flower or lowest node and working upwards) are as follows:
Ovary (plants)
Longitudinal section of female flower of squash showing ovary, ovules, pistil, and petals
In the flowering plants, an ovary is a part of the female reproductive organ of the flower or gynoecium. Specifically, it is the part of the carpel which holds the ovule(s) and is located above or below or at the point of connection with the base of the petals and sepals. In this picture of a zucchini the petals and sepals are above the ovary and such a flower is said to have an inferior ovary; also referred to as epigynous. Above the ovary is the style and the stigma, which is where the pollen lands and germinates to grow down through the style to the ovary, and, for each individual pollen grain, to grow into one individual ovule. Some wind pollinated flowers have much reduced and modified ovaries. The carpel together with all the female components including ovules, placental tissue, style and stigma are called gynoecium. The carpel is considered to be a modified leaf. A pea shell is a good example of a carpel and shows the genetic and morphological relationship to a leaf.
Petal
Tetrameric flower of the Primrose Willowherb (Ludwigia octovalvis) showing petals and sepals
This tulip has dozens of petals.
A petal (from Ancient Greek petalon “leaf”, “thin plate”), regarded as a highly modified leaf, is one member or part of the corolla of a flower. The corolla is the name for all of the petals of a flower; the inner perianth whorl, term used when this is not the same in appearance (color, shape) as the outermost whorl (the calyx) and is used to attract pollinators based on its bright color. It is the inner part of the perianth that comprises the sterile parts of a flower and consists of inner and outer tepals. These tepals are usually differentiated into petals and sepals. The term “tepal” is usually applied when the petals and sepals are similar in shape and color. In a “typical flower the petals are showy and colored and surround the reproductive parts. The number of petals in a flower (see merosity) is indicative of the plant’s classification: eudicots (the largest group of dicots) having typically four or five petals and monocots and magnoliids having three, or some multiple of three, petals.
There exists considerable variation in form of petals among the flowering plants. The petals can be united towards the base, forming a floral tube. In some flowers, the entire perianth forms a cup (called a calyx tube) surrounding the gynoecium, with the sepals, petals, and stamens attached to the rim of the cup.
The flowers of some species lack or have very much reduced petals. These are often referred to as apetalous. Examples of flowers with much reduced perianths are found among the grasses.
The petals are usually the most conspicuous parts of a flower, and the petal whorl or corolla may be either radially or bilaterally symmetrical. If all of the petals are essentially identical in size and shape, the flower is said to be regular or actinomorphic (meaning ‘ray-formed’). Many flowers are symmetrical in only one plane (i.e., symmetry is bilateral) and are termed irregular or zygomorphic (meaning yoke- or pair-formed). In irregular flowers, other floral parts may be modified from the regular form, but the petals show the greatest deviation from radial symmetry. Examples of zygomorphic flowers may be seen in orchids and members of the pea family. The petal is the colorful, often showy part of a plant.
Inflorescence is the shoot bearing flowers and no leaves. Also it is a group of flowers attached to a common axis in a specific arrangement. Flower is single when one flower per stem or the flowers are greatly spread-apart as to appear they do not arise from the same branch (poppy).
Types of simple monopodial inflorescences
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Raceme – is a flower spike with flowers that have stalks of equal length. The stem tip continues to grow and produce more flowers with the bottom flowers open first and blooming progresses up the stem (lily of the valley, digitalis).
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Spike – when flowers arising from the main stem are without individual flower stalks. The flowers attach directly to the stem (plantain).
Corymb – a grouping of flowers where all the flowers are at the same level, the flower stalks of different lengths forming a flat-topped flower cluster (apple).
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Umbel – were all the flower stalks rising from the same point of the same length, the flower head is rounded like an umbrella (cherry, onion).
Capitulum – the flowers are arranged into a plate composed of many separate unstalked flowers, the single flowers are called florets and are packed close together. The typical arrangement of flowers in the Asteraceae family (dandelion, sunflower).
Head – the flowers are arranged into a round composed of many separate unstalked flowers (clover).
Spadix – consisting of a single fleshy axis with many small sessile flowers (female Inflorescence in corn).
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Types of compound monopodial inflorescences
Compound umbel – is an umbel where each stalk of the main umbel produces another smaller umbel of flowers (dill, carrot).
Compound corymb (rowan-tree).
Compound spike (wheat, barley).
Compound raceme (rice, oat).
Fruits
Fruits are the containers in which the plant puts its seeds. They are not all fruits as we think of them, but have many different forms. Some are fleshy with parts we like to eat, some are dry, some are heavy and are designed to be dispersed by falling and rolling away from the parent plant, some have wings or fluffy tails to enable them to be caught by the wind to be dispersed.
Fruits are divided into Fleshy Fruits, and Dry Fruits.
Fleshy Fruits can be subdivided again into those formed from a single flower and those formed from a group of flowers. They can have one seed or several seeds in.
Fleshy Fruits formed from a single flower are classified as: Berry, Drupe, Aggregation of Drupes, Pome, Hesperidium. Some authorities also give these separate status: Hep, Pseudocarp, Pepo.
Fleshy Fruits which grow from a group of flowers are: Sorosis, Synconium, Coenocarpium.
Dry Fruits can be divided into those in which the seeds are contained in a seedpod of some sort which opens to release the seeds (called Dehiscent), and those in which there isn’t a seedpod which opens (Indehiscent).
Dry Dehiscent Fruits are Follicle, Legume, Silique, Capsule. Some authorities separate these further.
Dry Indehiscent Fruits are: Achene, Nut, Samara, Caryopsis. Some people sub-divide some of these further. There are also Schizocarpic Fruits.
Knowing the type of fruit a plant has might help you to identify it, and might also help you to know when the seeds are ready to harvest.
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FLESHY FRUITS |
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Berry A Berry is a single fleshy fruit without a stone, usually containing a number of seeds. This is a Kiwi Fruit (Actinidia chinensis). Other fruits of this type are: Banana (Musa), Coffee (Coffea arabica), Currant (Ribes), Pasionfruit (Passiflora), Pepper (Capsicum), Tomato (Lycopersicon esculentus). |
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A Drupe is a single fleshy fruit with a hard stone which contains the single seed. This is a Cherry (Prunus avium). Other fruits of this type are: Apricot (Prunus armeniaca), Plum (Prunus x domestica), Coconut (Cocos nucifera), Olive (Olea europaea), Peach (Prunus persica), Sloe (Prunus spinosa). |
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An Aggregation of Drupes is a fleshy fruit, made up of many drupes but formed from a single flower, each drupe containing one seed. This is a Raspberry (Rubus idaeus). Other fruits of this type are: Loganberry (Rubus), Blackberry (Rubus fruticosus). |
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A Pome is a fleshy fruit with a thin skin, not formed from the ovary but from another part of the plant. These are sometimes called Accessory Fruits. The seeds are contained in chambers in the centre of the fruit. This is an Apple (Malus domestica). Other fruits of this type are: Firethorn (Pyracantha), Hawthorn (Crataegus), Medlar (Mespilus germanica), Pear (Pyrus communis), Quince (Cydonia oblonga). |
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A Hesperidium is a berry with a tough, aromatic rind. This is an Orange (Citrus sinensis). Other fruits of this type are all Citrus fruits: Citron (Citrus medica), Grapefruit (Citrus x paradisi), Kumquat (Fortunella), Lemon (Citrus limon), Lime (Citrus aurantifolia). |
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A Pseudocarp is a false fruit, because it does not contain the seeds. The seeds are achenes, on the outside of a fleshy fruit. This is a Strawberry (Fragaria x ananassa). |
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FLESHY FRUITS |
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There are a few fruits formed from a group of flowers (inflorescence) rather than just one, but which form only one fruit. These are Sorosis, as in the Mulberry (Morus), Syngonium, as in the Fig (Ficus), and Coenocarpium, as in the Pineapple (Ananas). |
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A Follicle is a dry dehiscent fruit which splits on one side only. It may contain one or many seeds. This is the fruit of a Columbine (Aquilegia). Other fruits of this type are: Delphinium (Delphinium), Larkspur (Consolida), Love in a Mist (Nigella damascena), Milkweed (Asclepias), Peony (Paeonia). |
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Legume A Legume is a dry dehiscent pod that splits on two sides. This is the fruit of a Sweet Pea (Lathyrus odoratus). Other fruits of this type are all in members of the Pea Family (Leguminosae/Fabaceae): Acacia (Acacia), Alfalfa (Medicago sativa), Liquorice (Glycyrrhiza glabra), Flamboyant (Delonix regia), Pea (Pisum sativa), Peanut (Arachis hypogaea), Redbud (Cercis occidentalis), Runner Bean (Phaseolus coccineus), Wisteria (Wisteria). |
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A Lomentum is a dry dehiscent fruit, a legume constricted between the seeds. This is the fruit of a Golden Chain Tree (Laburnum anagyroides). Other fruits of this type are: Sophora (Sophora), Tick Trefoil (Desmodium). |
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A Silique is a dry dehiscent fruit. It is long and thin, splits down the two long sides, and has a papery membrane (the septum) between the two halves. This is the fruit of a Wallflower (Erysimum cheiri). Other fruits of this type are all in members of the Cabbage Family (Brassicaceae): Aubrieta (Aubrieta x cultorum), Cabbage (Brassica olearacea), Honesty (Lunaria annua), Radish (Raphanus sativus). A silique which is less than twice as long as broad is called a Silicula. |
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Capsule A Capsule is the most common fruit type. A Capsule is a dry fruit which splits open to release the seeds. These plants all have fruit capsules: Cotton (Gossypium), Eucalyptus (Eucalyptus), Horse Chestnut (Aesculus hippocastanum), Jimson Weed (Datura), Mahogany (Afzelia), Witch Hazel (Hamamelis). There are several types of Capsule, depending on how the fruit splits. |
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A Valvate Capsule is a dry dehiscent fruit in which the tips of the seed capsule split. This is the fruit of a Campion (Silene). Other fruits of this type are: Jacob’s Ladder (Polemonium), Pink (Dianthus), Primrose (Primula). |
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Porose Capsule A Porose Capsule is a dry dehiscent fruit, opening with pores or holes around the top. This is the fruit of a Poppy (Papaver). Other fruits of this type are: Blue Poppy (Meconopsis), Prickly Poppy (Argemone). |
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Loculicidal Capsule A Loculicidal Capsule is a dry dehiscent fruit, splitting along the locule (midrib of each ovary). This is the fruit of Stinking Gladwyn (Iris foetidissima). Other fruits of this type: Evening Primrose (Oenothera), Valotta (Cyrtanthus elatus), and members of the Violet and Lily Families. |
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Circumscissile Capsule A Circumscissile Capsule is a dry dehiscent fruit, opening by splitting through the centre of the fruit, so that the top of the capsule lifts off like a lid. An example of this type of fruit is Pimpernel (Anagallis) A Septicidal Capsule splits along the septa (joints of the ovary) as in the Foxglove (Digitalis). |
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Achene An Achene is a single-seeded dry indehiscent fruit in which the seedcoat is not part of the fruit coat. This is the fruit of a Sunflower (Helianthus annuus). Other fruits of this type are: Buttercup (Ranunculus), Clematis (Clematis), Coreopsis (Coreopsis), Dahlia (Dahlia), English Marigold (Calendula), Zinnia (Zinnia). |
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A Cypsela is a single-seeded dry indehiscent fruit that develops from a one part inferior ovary (on the stalk side of the flower). They are sometimes included with Achenes. This is the fruit of a Dandelion (Taraxacum officinale). Other fruits of this type are found in the same plant family, the Daisy Family (Asteraceae). |
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A Nut is a large single hardened achene. This is a Chestnut (Castanea sativa). Other fruits of this type are: Acorn (Quercus), Hazel (Corylus avellana), Hickory (Carya). |
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This is not a classification that seems to be recognised everywhere, but the Mint Family (Lamiaceae) is a very large plant family, and has a particular type of seed which is not quite any of the normal ones, so I thought it should be included somewhere. The fruits of this family are single-seeded achene-like nutlets, which are held at the bottom of the calyx. This is the fruit of a Salvia (Salvia). All members of the Mint Family (Lamiaceae) have this type of fruit. |
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A Caryopsis is a simple dry indehiscent fruit, like an achene, but with the seedcoat fused with the fruit coat. This is the fruit of Sweetcorn (Zea). Other fruits of this type are all members of the Grass Family (Poaceae): Barley (Hordeum), Oats (Avena), Rice (Oryza), Rye (Secale), Wheat (Triticum). |
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A Samara is an independent dry indehiscent fruit which has part of the fruit wall extended to form a wing (i.e. not a winged seed inside another type of seed pod). This is the fruit of a Maple (Acer). This is a Schizocarpic Samara, because the fruit splits into its separate Samaras. Other fruits of this type are: Ash (Fraxinus) – also Schizocarpic, Elm (Ulmus). |
SEED
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Seed – the part of a flowering plant that contains the endosperm and embryo. It will develop into a new plant if sown; a fertilized and mature ovule. Embryo is the product of repeated mitotic division of the zygote.
Literature
1. Botany / Randy Moore, W.Denis Clark, Kingsley R.Stern, Darrell Vodopich. – Dubuque, IA, Bogota, Boston, Buenos Aires, Caracas,Chicago, Guilford, CT, London, Madrid, Mexico City, Sydney, Toronto: Wm.C.Brown Publishers.- 1994.-
2. Kindsley R. Stern. Introductory plant biology-
3. Gulko R.M. Explanatory Dictionary of Medicinal Botany- Lviv: LSMU, 2003.-200 p.
4. Raven, P. H., R. F. Evert, & S. E. Eichhorn. Biology of Plants, 7th ed., page 9. (
5. Harold C. Bold, C. J. Alexopoulos, and T. Delevoryas. Morphology of Plants and Fungi, 5th ed., page 3. (New York: Harper-Collins, 1987).
Prepared by ass. prof. Shanayda M.I.
