Garden Terms: Reproductive Plant Morphology Seeds, Flowers, and Fruits. Anne Streich, Horticulture Educator

Transcription

1 EXTENSION Garden Terms: Reprodutive Plant Morphology Seeds, Flowers, and Fruits EC1257 Anne Streih, Hortiulture Eduator Seeds Seeds are a plant reprodutive struture, ontaining a fertilized emryo in an arrested state of development, surrounded y a hard outer overing. They vary greatly in olor, shape, size, and texture (Figure 1). Seeds are dispersed y a variety of methods inluding animals, wind, and natural harateristis (puffall of dandelion, wings of maples, et.). Seed Formation Pollination is the transfer of pollen from an anther to a stigma. This may our y wind or y pollinators. Cross pollinated plants are fertilized with pollen from other plants. Self-pollinated plants are fertilized with pollen from their own flowers. Fertilization is the union of the (male) sperm nuleus from the pollen grain and the (female) egg nuleus found in the ovary. If fertilization is suessful, the ovule will develop into a seed and the ovary will develop into a fruit. Seed Charateristis Figure 1. A seed is a small emryoni plant enlosed in a overing alled the seed oat. Seeds vary in olor, shape, size, and texture. Seed oats are the hard outer overing of seeds. They protet seed from diseases, insets and unfavorale environmental onditions. Water must e allowed through the seed oat for germination to our. Endosperm is a food storage tissue found in seeds. It an e made up of proteins, arohydrates, or fats. Emryos are immature plants in an arrested state of development. They will egin growth when environmental onditions are favorale. Germination is the proess in whih seeds egin to grow. Extension is a Division of the Institute of Agriulture and Natural Resoures at the University of Neraska Linoln ooperating with the Counties and the United States Department of Agriulture. University of Neraska Linoln Extension eduational programs aide with the nondisrimination poliies of the University of Neraska Linoln and the United States Department of Agriulture. 2007, The Board of Regents of the University of Neraska on ehalf of the University of Neraska Linoln Extension. All rights reserved.

2 Seed Dormanies Seed oat dormany is a physial ondition in whih the seed oat is impermeale to water and oxygen. In order to reak seed oat dormanies, the seed oat needs to e softened or raked. Methods used to reak seed oat dormany inlude sand paper, hot water, weathering, fire, miroorganisms, and passage through the digestive system of animals. The proess of physially reaking the seed oat dormany is alled sarifiation. Examples of plants having seed oat dormany inlude honeyloust, Kentuky offeetree and linden. Emryo dormany is a physiologial ondition of the emryo. This type of dormany requires a speifi period of old or heat treatment in order for germination to our. This temperature treatment is alled stratifiation. Examples of plants having emryo dormany inlude elm, with hazel, and dogwood. Doule dormany is when the seed has oth seed oat and emryo dormany. An example is redud seed. Germination Flowers Flowers ontain the sexual reprodutive parts of the plant (Figure 2). Plants are often grown for flower olor and fragrane. Flower Charateristis Sepals are leaf-like strutures that protet the flower ud. They are usually green and olletively are alled the alyx. Sometimes they are highly olored and similar in appearane to petals. Petals are usually the highly olored strutures of the flower. They are olletively alled the orolla. Tepal is the olletive term used for sepals and petals when they are not easily distinguishale. Pistil is the female part of the flower, usually made up of a stigma, style, ovary(s) and ovule(s). Stigmas are at the top of the style and reeive pollen. They are ommonly flattened and stiky. Germination is the resumption of ative growth of the emryo. Prior to any visual signs, the seed must imie water through the seed oat. The seed must also e in proper environmental onditions; that is, exposed to oxygen, favorale temperatures, and in some ases, light. Styles are long stalks that onnet the stigma and ovary. Ovaries develop into fruit after fertilization and ontain ovules. Anther Stigma Petal Style Ovary Filament Sepal Figure 2. The reprodutive struture of a plant is found in its flower.

3 Ovules are loated in the ovary and are unfertilized, immature seed whih ontain geneti information from the maternal (female) parent plant. Stamen is the male part of the flower, usually made up of anthers and filaments. Anthers are the pollen produing organ. Filaments are long supporting stalks for the anthers. Pollen is a fine, powder-like reprodutive struture ontaining geneti information from the paternal (male) parent plant. Reeptale is the ase of the flower. Pediel is the stalk that diretly supports a flower or fruit (Figure 3). Pedunle is the primary stalk supporting a single or luster of flowers or fruits. Infloresene refers to how flowers are arranged on a floral stem. The most ommon floral arrangements are solitary, spike, raeme, panile, omposite, and umel (Figure 4). Flower Types Complete flowers ontain the stamen, pistil, petals, and sepals. Flowers are alled inomplete if they have one or more of these parts missing. Figure 3. Pediel Pedunle The pediel is the stalk that diretly holds the flower or fruit, while the pedunle is the primary stalk that supports a single or luster of flowers or fruits. Perfet flowers ontain oth the male and female flower parts within eah flower. If either the male or female flower parts are missing, the flower is alled imperfet. Solitary Spike Raeme Pistillate (female) flowers are those whih possess a funtional pistil or pistils ut lak stamens. Staminate (male) flowers are those whih possess funtional stamens ut lak a pistil. Plant Types Moneious plants have separate male and female flowers on the same plant. Examples are oak and orn. Dioeious plants have male and female flowers on different plants. Examples are uffalograss (Figure 5) and holly. Figure 4. Panile Umel The most ommon infloresene types inlude: solitary a single flower with the pediel attahed to the stem; spike stalkless flowers; raeme a luster of flowers on individual stalks (pediels); panile a luster of flowers on flower stalks that have repeated ranhing; and umel a luster of flowers that have stalks that radiate from the same point at the top of the pedunle.

4 Figure 5. Male (a) and female () uffalograss flowers grow on separate plants, indiating it is a dioeious plant. Fruits Fruits are the ripened ovaries of flowers. They an vary in size, olor, form and texture. Dry fruits (Figure 6) have fruit walls that eome papery or leathery as they mature and may eome quite hard. Dehisent fruits split or open at maturity. Examples inlude legumes (ean family), apsules (euonymus), folliles (milkweed), and siliques/sililes (mustards) (Figure 6a-6d). Indehisent fruits do not open at maturity. Examples inlude samaras (maple), nuts (oak), ahenes (sunflower), and shizoarps (dill) (Figure 6e-6g). Fleshy fruits (Figure 7) are usually soft and juiy. Examples inlude drupes (prunes and peahes), pomes (pears and apples), erries (tomatoes), pepos (melons), and hesperidium (itrus). Aggregate fruits (Figure 8) develop from a single flower whih has many ovaries. The flower appears as a simple flower with one orolla, one alyx, and one stem ut with many pistils (Figure 9). The ovaries are fertilized separately and independently. Examples inlude strawerry, rasperry, and lakerry. Multiple fruits are derived from a tight luster of separate, independent flowers orne on a single struture. Eah flower will have its own alyx and orolla. Examples inlude pineapple, fig, and mulerry. Cones are the fruit of gymnosperms. They are not true fruits eause they do not develop from an ovary. Seed found in ones are therefore said to e naked. Seeds of gymnosperms are found inside near the ase of the one sales. In some gymnosperms, suh as junipers and yews, the seed is found inside a fleshy one known as an aril. In ginkgo, the seed is found inside a fleshy overing that is messy and malodorus. For these reasons, only male ginkgo trees should e used in landsapes (Figure 10). Simple fruits develop from a single ovary.

5 Dehisent Fruits Legume Capsule d Follile Silile Indehisent Fruits e f g h Samara Nut Ahene Shizoarp Figure 6. Dry fruits are lassified as either dehisent or indehisent, depending on whether they split open at maturity. Legumes (a) ontain several seeds and open along two sides. They are found in the ean family (Faaeae). Capsules () ontain many seeds and split along more than two sides and often ontain separate ompartments. Folliles () ontain several seeds and open along one seam. Siliques/sililes (d) leave a thin partition in whih seeds are attahed after the fruit opens. Siliques/sililes are found in the mustard family (Brassiaeae). Samaras (e) are winged fruits. Nuts (f) are hard, one-seeded fruits. Aorns, walnuts, and hestnut are examples of nuts. Ahenes (g) are one-seeded fruits without wings. Shizoarps (h) split to form one-seeded segments.

6 Drupe d Pome e Berries Figure 7. a Pepos Hesperidiums Drupes (a) ontain one seed whih is surrounded y a hard stony layer (pit) and an outside fleshy layer (plum, herry, viurnum). Pomes () have several seeds that are ontained near the enter of the fruit (apple and pear). Berries () have two or more seeds that are found in a fleshy layer that omprises the entire fruit (tomato). Pepos (d) are speialized erries with a hard rind enlosing a fleshy interior ontaining several seeds (uumer, melons, squash). Hesperidiums (e) are speialized erries with a leathery rind and several juiy setions in the interior (itrus). Figure 8. Aggregate fruits form from a single flower. Examples of plants with an aggregate fruit inlude: (a) tuliptree (aggregate of samaras); () lakerry (aggregate of drupes); () sweetgum (aggregate of apsules).

7 ahenes Figure 9. The strawerry flower has many pistils, whih are loated in the enter of the flower and are surrounded y several stamens (a). The fruit is an aggregate of ahenes (tannish-orange strutures) whih are held in a fleshy red enlarged reeptale (). a Figure 10. Cones and naked seeds are the fruit of gymnosperms. Examples inlude a one from ponderosa pine (a); an aril from yew (); and a seed from ginkgo ().