Sepals Sepals Adrienne HK Roeder, California Institute of Technology, Pasadena, California, USA Published online: May 2010 References Abstract Sepals are the outermost organs of a flower. They are sterile and generally green leaf‐like organs that surround and protect the developing reproductive structures inside the bud before the flower blooms. The sepals are the first organs initiated from the floral meristem and quickly grow to cover the floral meristem and initiating organ primordia. Sepal organ identity is traditionally thought to be specified by the A function in the ABC model. Sepals often contain specialised cell types such as hair cells or giant cells, which are present on the outer surface of Arabidopsis sepals. The sepals and petals in the flower interact with the environment by both attracting pollinators as well as defending against predators and abiotic factors such as the weather. Current and future research on the development of sepals will lead to a better understanding of floral organ formation as well as underlying principles of cell division and growth. Key Concepts: The perianth is composed of the sterile organs of the flower, which are the set of sepals (calyx) and the set of petals (corolla).

Although generally sepals are green photosynthetic protective organs, some sepals are showy organs similar to petals and designed for attracting pollinators. Sepals serve their protective function by overlapping such that they completely cover the developing bud. Sepals generally contain defensive cell types including hair cells and produce toxic chemicals to defend the developing reproductive organs from predators. Arabidopsis sepals have a characteristic pattern of diverse cell sizes including giant cells on the outer surface. The four Arabidopsis sepals are the first organs initiated from the floral meristem and are formed in a whorled phyllotaxy. APETALA1 (AP1), APETALA2 (AP2) and SEPALLATA1–4 (SEP1–4) specify sepal organ identity. After fertilisation, sepals often senesce and abscise. Keywords: flowers; reproduction; angiosperms; bracts; buds; giant cells Figure 1. Arabidopsis sepals. (a) Mature Arabidopsis flower (stage 14) showing the outer whorl of four sepals, followed by four petals, six stamens and two carpels at the centre of the flower.

(b) Scanning electron micrograph (SEM) of the outer (abaxial) side of the sepal showing the characteristic cell size pattern including giant cells (false coloured red). (c) High magnification view of the abaxial sepal epidermis showing the diversity of cell sizes (giant cells are false coloured red) and the presence of stomata (false coloured green) for gas exchange. (d) High magnification view of the inner (adaxial) side of the sepal showing that the cells are of a more uniform size and interspersed with a few stomata (false coloured green). Two ball‐shaped pollen grains are present. Figure 2. Development of the Arabidopsis sepal. (a) Scanning electron micrograph (SEM) of the inflorescence meristem (m) from an Arabidopsis thaliana Landsberg erecta plant. The surrounding flower primordia are visible. The sepal primordia emerge as ridges on the flanks of the late stage 3 floral meristem. The sepal primordia grow to cover the floral meristem, whereas the stamen primordia initiate at stage 5.

The sepals completely cover the floral meristem at stage 6. (b) A stage 9 bud shows the development of the specialised cell size pattern including giant cells (g) and the differentiation of guard cells (gc) proceeding basipetally (from top to bottom). Note the trichome (t) at the top of the sepal. (c) At stage 12 bud, the sepals remain closed. (d) In stage 13, the petals and stamens push the sepals open as the flower blooms. (e) At stage 14, the flower is completely open and the sepal is fully mature. (f) At stage 16, the sepals senesce, turn yellow and are abscised. Figure 3. ABC model of floral organ identity. The ABC model postulates that there are three activities that act alone or concert to specify the identity of the floral organs. A function specifies sepals, A+B function specifies petals or lodicules, B+C function specifies stamens and C function alone specifies carpels. Whether the grass lemma or palea can be considered first whorl oranges and whether they are specified by an A function is a current subject of investigation.

References Ambrose BA, Lerner DR, Ciceri P et al. (2000) Molecular and genetic analyses of the silky1 gene reveal conservation in floral organ specification between eudicots and monocots. Molecular Cell 5: 569–579. Bossinger G and Smyth DR (1996) Initiation patterns of flower and floral organ development in Arabidopsis thaliana. Development 122: 1093–1102. Bowman JL, Alvarez J, Weigel D, Meyerowitz EM and Smyth DR (1993) Control of flower development in Arabidopsis thaliana by Apetala1 and interacting genes. Development 119: 721–743. Bowman JL, Smyth DR and Meyerowitz EM (1989) Genes directing flower development in Arabidopsis. Plant Cell 1: 37–52. Bowman JL, Smyth DR and Meyerowitz EM (1991) Genetic interactions among floral homeotic genes of Arabidopsis. Development 112: 1–20.

Chen X (2004) A microRNA as a translational repressor of APETALA2 in Arabidopsis flower development. Science 303: 2022–2025. Coen ES and Meyerowitz EM (1991) The war of the whorls – genetic interactions controlling flower development. Nature 353: 31–37. Dinneny JR, Yadegari R, Fischer RL, Yanofsky MF and Weigel D (2004) The role of JAGGED in shaping lateral organs. Development 131: 1101–1110. Ditta G, Pinyopich A, Robles P, Pelaz S and Yanofsky MF (2004) The SEP4 gene of Arabidopsis thaliana functions in floral organ and meristem identity. Current Biology 14: 1935–1940. Drews GN, Bowman JL and Meyerowitz EM (1991) Negative regulation of the Arabidopsis homeotic gene AGAMOUS by the APETALA2 product.

Cell 65: 991–1002. Gregis V, Sessa A, Colombo L and Kater MM (2006) AGL24, SHORT VEGETATIVE PHASE, and APETALA1 redundantly control AGAMOUS during early stages of flower development in Arabidopsis. Plant Cell 18: 1373–1382. Honma T and Goto K (2001) Complexes of MADS‐box proteins are sufficient to convert leaves into floral organs. Nature 409: 525–529. Irish VF and Sussex IM (1990) Function of the apetala‐1 gene during Arabidopsis floral development. Plant Cell 2: 741–753. Jofuku KD, den Boer BG, Van Montagu M and Okamuro JK (1994) Control of Arabidopsis flower and seed development by the homeotic gene APETALA2. Plant Cell 6: 1211–1225.

Keck E, McSteen P, Carpenter R and Coen E (2003) Separation of genetic functions controlling organ identity in flowers. EMBO Journal 22: 1058–1066. Lewis MW, Leslie ME and Liljegren SJ (2006) Plant separation: 50 ways to leave your mother. Current Opinion in Plant Biology 9: 59–65. Litt A (2007) An evaluation of A‐function: evidence from the APETALA1 and APETALA2 gene lineages. International Journal of Plant Sciences 168: 73–91. Lohmann JU, Hong RL, Hobe M et al. (2001) A molecular link between stem cell regulation and floral patterning in Arabidopsis. Cell 105: 793–803. Mandel MA, Bowman JL, Kempin SA et al. (1992a) Manipulation of flower structure in transgenic tobacco. Cell 71: 133–143.

Mandel MA, Gustafson‐Brown C, Savidge B and Yanofsky MF (1992b) Molecular characterization of the Arabidopsis floral homeotic gene APETALA1. Nature 360: 273–277. Melaragno JE, Mehrotra B and Coleman AW (1993) Relationship between endopolyploidy and cell size in epidermal tissue of Arabidopsis. Plant Cell 5: 1661–1668. Mizukami Y and Ma H (1992) Ectopic expression of the floral homeotic gene AGAMOUS in transgenic Arabidopsis plants alters floral organ identity. Cell 71: 119–131. Nagasawa N, Miyoshi M, Sano Y et al. (2003) SUPERWOMAN1 and DROOPING LEAF genes control floral organ identity in rice. Development 130: 705–718.

Ohno CK, Reddy GV, Heisler MG and Meyerowitz EM (2004) The Arabidopsis JAGGED gene encodes a zinc finger protein that promotes leaf tissue development. Development 131: 1111–1122. Pelaz S, Ditta GS, Baumann E, Wisman E and Yanofsky MF (2000) B and C floral organ identity functions require SEPALLATA MADS‐box genes. Nature 405: 200–203. Pelaz S, Gustafson‐Brown C, Kohalmi SE, Crosby WL and Yanofsky MF (2001a) APETALA1 and SEPALLATA3 interact to promote flower development. Plant Journal 26: 385–394. Pelaz S, Tapia‐Lopez R, Alvarez‐Buylla ER and Yanofsky MF (2001b) Conversion of leaves into petals in Arabidopsis. Current Biology 11: 182–184. Pinyopich A, Ditta GS, Savidge B et al.

(2003) Assessing the redundancy of MADS‐box genes during carpel and ovule development. Nature 424: 85–88. Pnueli L, Hareven D, Rounsley SD, Yanofsky MF and Lifschitz E (1994) Isolation of the tomato AGAMOUS gene TAG1 and analysis of its homeotic role in transgenic plants. Plant Cell 6: 163–173. Smyth DR, Bowman JL and Meyerowitz EM (1990) Early flower development in Arabidopsis. Plant Cell 2: 755–767. Sridhar VV, Surendrarao A and Liu Z (2006) APETALA1 and SEPALLATA3 interact with SEUSS to mediate transcription repression during flower development. Development 133: 3159–3166. Theissen G (2001) Development of floral organ identity: stories from the MADS house. Current Opinion in Plant Biology 4: 75–85.

Vrebalov J, Pan IL, Arroyo AJ et al. (2009) Fleshy fruit expansion and ripening are regulated by the tomato SHATTERPROOF gene TAGL1. Plant Cell 21: 3041–3062. Warner KA, Rudall PJ and Frohlich MW (2009) Environmental control of sepalness and petalness in perianth organs of waterlilies: a new Mosaic theory for the evolutionary origin of a differentiated perianth. Journal of Experimental Botany 60: 3559–3574. Wellmer F, Alves‐Ferreira M, Dubois A, Riechmann JL and Meyerowitz EM (2006) Genome‐wide analysis of gene expression during early Arabidopsis flower development. PLoS Genetics 2: e117. Wellmer F, Riechmann JL, Alves‐Ferreira M and Meyerowitz EM (2004) Genome‐wide analysis of spatial gene expression in Arabidopsis flowers. Plant Cell 16: 1314–1326.

Whipple CJ, Ciceri P, Padilla CM et al. (2004) Conservation of B‐class floral homeotic gene function between maize and Arabidopsis. Development 131: 6083–6091. Whipple CJ and Schmidt RJ (2006) Genetics of grass flower development. Advances in Botanical Research Incorporating Advances in Plant Pathology 44: 385–424. Whipple CJ, Zanis MJ, Kellogg EA and Schmidt RJ (2007) Conservation of B class gene expression in the second whorl of a basal grass and outgroups links the origin of lodicules and petals. Proceedings of the National Academy of Sciences of the USA 104: 1081–1086. Xu B, Li Z, Zhu Y et al. (2008) Arabidopsis genes AS1, AS2, and JAG negatively regulate boundary‐specifying genes to promote sepal and petal development. Plant Physiology 146: 566–575.

Further Reading Endress PK (1994) Diversity and Evolutionary Biology of Tropical Flowers. Cambridge: Cambridge University Press. Heywood VH, Brummitt RK, Culham A and Seberg O (2007) Flowering Plants Families of the World. Buffalo: Firefly Books Ltd. Meyerowitz EM (1994) The genetics of flower development. Scientific American 271: 56–65. Soltis DE, Leebens‐Mack JH and Soltis PS (eds) (2006) Developmental genetics of the flower. In: Callow JA (Series ed.) Advances in Botanical Research Incorporating Advances in Plant Pathology, vol. 44. San Diego: Academic Press. Stebbins GL (1974) Flowering Plants: Evolution Above the Species Level. Cambridge, MA: The Belknap Press of Harvard University Press. Related Sub-Topics: Flower | Parts of a Flower | Angiosperm Morphology Flower | Biology@TutorVista.com Back to Top Flowers are the reproductive organs of plants. Flower is the modified vegetative shoot and is meant for sexual reproduction.

Flower arises from a modified leaf called bract. It consists of a very short axis on which whorls of different parts of the flower are present. Parts of a Flower Flowers are diverse in gross appearance but the basic parts which make up the flower are basic throughout. Flower is the specialized and modified shoot. The following are the recognized parts of the flower: Peduncle Peduncle is the stalk of a flower. Receptacle Receptacle is the stem portion, it is found at the base in the center of the flower. The internodes are short and the number of leaves is small. Hence, receptacle is not usually a large part of the flower. Sepals Sepals form the outermost whorl of the floral structure. They are mostly but not always green and are leaf-like in appearance. Sepals are similar to the foliage leaves of the plant. Sepals are collectively known as the Calyx. The major function of the calyx is the protection of flower parts during early development of the flower or the bud. Petals Petals are present above the sepals whorl. Petals are larger than the sepals, they are brightly colored, leaf-like, broad and are thin organs.

The petals collectively are known as the Corolla. Corolla is the attractive part of the flower. They provide additional protection and attract insects to facilitate pollination of the flower. The leaf-like organs, the sepals and the petals are together known as the perianth of the flower. They are similar in appearance. Carpels Carpels are one or more in number and are located in the upper center of the flower. Collectively the carpels are known as gynoecium. Carpels are made of three parts: Ovary. Style and Stigma. Ovary is the structure present at the base of the carpel. It is an enlarged narrow region bearing one or more ovules. Style is the slender, neck-like portion of the carpel the leads to the ovary. Stigma is of variety of shapes and sizes. It present at the tip of the carpel and is sticky to collect pollen grains. Stamens Stamens are located inside the corolla and are leaf-like appearance. Stamens are the male part of the flower and produces pollen. Stamens consists of a filament and an anther. Stamens are collectively called androecium.

Anther is the sac located at the tip of the filament that contains pollen. Filament is the stalk that connects to and holds up the anther. Nectaries are often associated with flowers and are found at the receptacle, nectaries produce sugary nectar which attracts insects. Bract Back to Top Flower consists of a stalk and is called pedicel. The flower is described as sessile if the pedicel is absent. Flowers are known as ebracteate in the absence of bracts. Bract-like green structures are present on the pedicel and are called bracteoles and the flower with presence of bractiole is called bracteolate and absence of bracteoles is described as ebracteolate. Bracts are of various types: Foliaceous: Leaf-like bracts as in Adhantoda. Petaloid: Petal like bracts, peatloids is bracts where they are large and colored as in Bougainvillea. Involucre of bracts: Here many bracts form one or more whorled structures called involucres. Example: Head inflorescence of Helianthus.

Spathe: Special type of bract covering the flowers in spadix inflorescence. Example: Aroids, Cocos nucifera. Calyx Corolla makes up the second whorl of the flower and it is composed of petals. They are brightly colored, making the corolla conspicuous, and attractive. Petals are also scented in many cases. They help attracting insects for pollination. The corolla is described as polypetalous if the petals are free from one another. Example - Crotalaria. They are described gamopetalous if the petals are fused or united. Example - Nerium. The number of petals in the flower is a feature for classification of plants. In dicot plants, most frequently four or five petals are present. In flowers of monocot plants usually three or six petals are seen. The corolla may be either radially or bilaterally symmetrical. If the petals are in radial symmetry, all the petals are identical in size and shape the flower is said to be regular or actinomorphic. Example - Lily, buttercup.

Many flowers are bilaterally symmetrical, that is they are symmetrical in only one plane, these flowers are said to be irregular or zygomorphic. Example - Orchids and members of pea family. Androecium Back to Top The stamens in the flower is called androecium. The androecium forms a whorl surrounding the gynoecium and is inside the perianth. Stamens can be free or fused in may ways, like some stamens be fused but not all. It also can be, the filaments fused and the anthers free and the filaments free and the anthers fused. Usually the anthers have two locules, in some one of the locules may fail to develop or the two locules may merge late in development to give a single locule. Androphore is the term given to a column formed from the fusion of multiple filaments. The anther can be attached to the filament in two ways basifixed and dorsifiexed. Basifixed is where the anther is attached at its base to the filament. Dorsifixed, here the anther is attached at its center to the filament, usually versatile.

Back to Top Pistil is the female reproductive part of a flower. It is located centrally and consists of a swollen base, which is the ovary. The ovary contains the ovules which are the potential seeds; a stalk or style and a stigma which the pollen receptive tip. Pistil in collective sense forms the gynoecium. Pistil is the word used to describe each unit of the gynoecium. A pistil consist of a single carpel which can be a monocarpous or apocarpus gynoecium, in which case it is called a simple pistil. It also may be of fused carpels or a syncarpous gynoecium and is called a compound pistil. Placentation Back to Top Placentation in flowering plants occurs at position where the ovules are attached inside the ovary via the funiculi. The term placentation here refers to the arrangement of placentas inside a flower or fruit. The types of placentation are: Basal Placentation: Here the placenta is at the base or bottom of the ovary. It can be seen in a simple or compound carpel.

Apical Placentation: The placenta is the the apex position or the top of the ovary, it is also seen in simple or compound carpel. Parietal Placentation: It is found only in the compound carpel. The ovary is positioned in the ovary wall within a non-sectioned ovary. Axile Placentation: The ovary in axile placentation is sectioned by radial spokes with placentas in separate locules. Axile placentation is seen in compound carpels. Central Placentation: Central placentation is also known as free placentation. Here the placentae are arranged in a central column within a non-sectioned ovary and is seen in compound carpel. Marginal Placentation: This type of placentation is conspicuous in legumes and simple carpels, Here there is only one elongated placenta on one side of the ovary. Estivation Botany 101 -- Flower Parts Botany 101 Flower Parts A flower is a highly differentiated and specialized branch of the stem bearing modified leaves or flower parts. It is the site of sexual reproduction in these plants and is their most distinctive structure.

The great variety of forms acts as a guide in separating flowering plants into the major groups. Before we look at the different classifications of flowers, we must first learn the terms for the individual structures in the flower. Accessory Organs The following are known as accessory organs because they are not directly involved in pollination. Perianth - the outer floral parts, composed of the calyx and the corolla. Tepal - used when calyx and corolla are very similar and not easily distinguished as in Lilium catesbaei (pine lily). Calyx - the ring of sepals making up the outermost, leaflike part of the flower. Sepals are commonly green, but may be almost any color and serve primarily as protection for the other floral parts. Corolla - the inner set of leaflike parts lying just within the calyx and composed of petals . Petals are generally white or brightly colored to attract pollinating insects to their nectar. They also serve as protection for the innermost organs. Receptacle or torus - the apex of the pedicel upon which the organs of a flower are developed. Floral Bracts - modified leaves which can simulate petals and add the conspicuous part to otherwise inconspicuous flowers.

Examples are the red bracts surrounding the small Euphorbia pulcherrima (poinsettia) flowers; the purple, red, or white leaves enclosing the small white flowers of Bougainvillea spp. (bougainvillea); or the white leaves of Cornus florida (flowering dogwood). Many plants have floral bracts which are not colorful such as Fittonia vershaffeltii (silver nerve plant). Reproductive Organs Reproductive organs are directly involved in pollination and fertilization, hence their presence usually determines the survival of the species. Stamens - male reproductive organs attached to the receptacle in some species inside the corolla or in other species to the corolla itself. Each stamen is composed of: Filament - thin stalk which attaches the anther to the rest of the flower. Its attachment is called basal if it is at the lower end of the anther as in Tulipa spp. (tulip), and versatile if it is lateral, near the center of the anther as in Crinum spp. (crinum). Anther - lobed, oblong, bag-like appendage at the top of the filament which produces the pollen grains which develop the male germ cells.

Anthers are usually yellow and when young have from one to four cavities (cells) in which pollen grains arise. When mature, the anther usually contains two cavities from which the pollen grains are released by the formation of apical pores or longitudinal slits in the cavity wall. Pollen Grains - usually appear as tiny specks barely visible to the unaided eye, but are produced in such quantity that they often form a layer of powder. Each grain is usually two-celled, spherical, ovoid, or disk-like in appearance, whose surface is marked with ridges, spines, and germ spores. Pollen grains, collectively known as pollen, are so characteristic of the different species that they are used for identification purposes. In orchids and milkweeds pollen are in masses known as pollinia. Stamens are called opposite when they are opposite to the petals as in Vitis rotundifolia (muscadine grape) or Rhamnus caroliniana (Carolina buckthorn) and alternate when they alternate with the petals as in Viola odorata (garden violet).

The stamens are usually free or separate from each other, but in a few families they are united either by their filaments Hibiscus rosa-sinensis (hibiscus) and Lycopersicon esculentum (tomato) or by their anthers as in Helianthus annuus (sunflower). Pistils - the female reproductive organs usually occur in the very center of the flower and are often surrounded by the stamens, petals, and sepals. Flowers may have just one simple pistil [as in Lathyrus odoratus (sweet pea)], or two, three, four, five, or more separate pistils as in Consolida spp. (larkspur). A carpel refers to either a simple pistil or one of the segments of a compound pistil. United carpels are found in Dietes iridioides (African iris) and Antirrhinum majus (snapdragon). Pistils are usually flask- or bottle-shaped. They are composed of three parts: Style - the elongated stalk or neck connecting the ovary with the stigma.

Ovary - enlarged, bulbous, basal part of the pistil which bears the ovules (the egg-containing units which, after fertilization, become the seeds) attached either to its central axis or to its inner wall. The tissue to which the ovules are attached is called the placenta . Each ovule usually contains one egg , the female gamete or sex cell. The ovule normally develops into a seed when fertilized. Generally there are two or more ovules per carpel. In some plants, only one may mature into a seed. The ovary normally develops into a fruit containing seeds. An example is the pod of Phaseolus lunatus (lima bean). Stigma - the tip of the pistil especially adapted to receive the pollen grains. The stigma may be expanded into a bulb or disk or divided into two or more slender parts. The stigma is often located atop a style. A pistil is said to be compound when several or many carpels become united. Carpels are united so that a compound ovary often contains as many cavities as there are carpels. In some flowers, a compound ovary becomes "one-celled" by the disappearance of the partitions between the different carpels as in Primula spp.

(primrose). Union of carpels may be so complete that it includes the styles and stigmas as well as the ovaries. We are now ready to list the different classifications of flowers according to the presence or absence of their parts: Complete flowers are made up of calyx, corolla, stamens, and a pistil or pistils (the four "regular parts"). Incomplete flowers lack one or more of the four regular parts of a complete flower as in all of the Fagaceae (oak family), Betulaceae (birch family) and Juglandaceae (walnut family). Perfect flowers have both stamens and pistils, but not necessarily sepals or petals. Imperfect flowers lack either stamens or pistils, and may or may not have sepals or petals. Naked flowers are without petals (apetalous) or sepals (asepalous) as in Zantedeschia spp. (calla lily). Apetalous flowers lack petals as in Elaeagnus pungens (silverthorn), Hydrangea spp. and Cornus florida (flowering dogwood).

Staminate (male) flowers have a stamen or stamens, but no functional pistils. Pistillate (female) flowers have a pistil or pistils, but no functional stamens. Three terms are applied to plants based on their flowering characteristics: Monoecious plants bear both staminate and pistillate flowers on the same plant as in Quercus spp. (oak) and Zea mays (corn). Dioecious plants bear staminate flowers on one plant and pistillate flowers on a different plant, hence the terms male and female plants. Ilex species (holly) and all cycads and many conifers are examples. Polygamous plants bear staminate, pistillate, and hermaphroditic (bisexual - both sexes present and functional in the same flower) flowers on the same plant. An example is Acer rubrum (red maple). Source: Botany Handbook for Florida, Revised Edition, Kathleen C. Ruppert, January 1999 -- This document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida.

UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication. d Sepals Protective leaf like enclosures for the flower - SAS - Biochemist View Full Document (d) Sepals – Protective leaf-like enclosures for the flower buds, usually green, collectively called calyx. Sometimes highly colored like the petal as in iris. (e) Receptacle – Part of flower stalk bearing the floral organs, at base of flower. (f) Pedicel – Flower stalk of an individual flower in an inflorescence. Materials: 1. Two types of flowers 2. Razor blade 3. Slides 4. Cover slip 5. Microscope 6. Distilled water Methods: 1. The flowers were examined and each set of the floral organs were carefully removed, beginning with the outermost organs. 2. A stamen was examined with the microscope.

Then the pollen was extracted, mounted with water on a slide and examined under the microscope. 3. The pistil was split lengthwise with a razor blade and the internal cavity of the ovary was noted. 4. All the observation was recorded. This preview has intentionally blurred sections. Sign up to view the full version. View Full Document Result: Floral Parts Flower 1 Flower 2 Sepals Two, large, overlapping and form a tube at the bottom, green in colour Five, small, separated, green in colour Petals Three, small, purple in colour, overlapping and form a tube at the bottom Five, big, yellow in colour, separeted Stamen Anther Five, moon-shaped and continued with filament, small, brown in colour Ten, elongated and continued with filament, big, brown in colour Pollen Round, rough Round, rough Filament Long, thin tube, fused with petals Short, thick tube, split from petals Pistil Stigma Irregular-shaped, small, green in colour, This is the end of the preview. Sign up to access the rest of the document.

TERM Tunku Abdul Rahman University College, Kampar SAS Biochemist - Fall 2013 Name: Choong Mel June Student ID: 12WAD00443 Group: AA1 Subject: AACB3214 Biodiversit exp 1 completed angiosperm - Reproductive structures | plant | Britannica.com Reproductive structures peanut General features The broad range of variation in the morphology and structure of nonreproductive (vegetative) organs within the angiosperms has been outlined above. There is a similarly broad range in the morphology and structure of the reproductive organs of the plant . Many vegetative buds sooner or later become flower buds. Flower buds are modified leaves borne on a short axis with very short internodes and no axillary buds. The floral axis has determinate growth, in that at some point it ceases to grow. Flowers , the reproductive tissues of the plant, contain the male and/or female organs. They may terminate short lateral branches or the main axis or both. Flowers may be borne singly (as in the daffodil and Magnolia ) or in clusters called inflorescences (e.g., bromeliads, snapdragons, and sunflowers).

Fruits are derived from the floral parts of the angiospermous plant. Rhododendrons in bloom along a trail. Photos.com/Jupiterimages Titan arum, or corpse flower (Amorphophallus titanum), featuring the largest … © alessandrozocc/Fotolia A complete flower is composed of four organs attached to the floral stalk by a receptacle ( Figure 11 ). From the base of the receptacle upward these four organs are the sepals , petals , stamens , and carpels . In dicots the organs are generally grouped in multiples of four or five (rarely in threes), and in monocots they are grouped in multiples of three. The sepals, the outermost layer, are usually green, enclose the flower bud, and collectively are called the calyx. Petals are the next layer of floral appendages internal to the calyx; they are generally brightly coloured and collectively are called the corolla. The calyx and corolla together compose the perianth . The sepals and petals are accessory parts or sterile appendages; though they protect the flower buds and attract pollinators, they are not directly involved with sexual reproduction.

When the colour and appearance of sepals and petals are similar, as in the tulip tree (Liriodendron tulipifera) and Easter lily (Lilium longiflorum), the perianth is said to be composed of tepals. Similar Topics liverwort Internal to the corolla are the stamens, spore-producing structures (microsporophylls) that are collectively called the androecium. In most angiosperms, the stamens consist of a slender stalk (the filament) that bears the anther (and pollen sacs), within which the pollen is formed. Small secretory structures called nectaries are often found at the base of the stamens and provide food rewards for pollinators. In some cases the nectaries coalesce into a nectary or staminal disc. In many cases the staminal disc forms when a whorl of stamens is reduced into a nectiferous disc, and in other cases the staminal disc is actually derived from nectary-producing tissue of the receptacle. At the centre of the flower are the carpels, collectively called the gynoecium.

Carpels are megasporophylls that enclose one or more ovules, each with an egg. After fertilization, the ovule matures into a seed, and the carpel matures into a fruit. Carpels, and thus fruit, are unique to angiosperms. A complete flower contains all four organs, while an incomplete flower is missing at least one. A bisexual (or “perfect”) flower has both stamens and carpels, and a unisexual (or “imperfect”) flower either lacks stamens (and is called carpellate) or lacks carpels (and is called staminate).

Species with both staminate flowers and carpellate flowers on the same plant (e.g., corn ) are monoecious , from the Greek for “one house.” Species in which the staminate flowers are on one plant and the carpellate flowers are on another are dioecious , from the Greek for “two houses.” Floral organs are often united or fused: connation is the fusion of similar organs—e.g., the fused petals in the morning glory ; adnation is the fusion of different organs—for example, the stamens fused to petals in the mint family ( Lamiaceae ). The basic floral pattern consists of alternating whorls of organs positioned concentrically: from outside inward, sepals, petals, stamens, and carpels ( Figure 12 ). It is possible in most cases to interpret the flower with respect to missing parts and/or the modification of parts to function as missing parts simply by positional relationships. In a complete five-merous flower (starting from the outside) there would be a whorl of five sepals, followed by an alternating whorl of five petals, followed by an alternating set of five stamens.

In the floral diagram ( Figure 12 ), the midline of each petal is midway between the midlines of two adjacent sepals. Because the whorls alternate, the midline of each stamen of the stamen whorl is between the midlines of two adjacent petals and on the midline of each sepal. When the petals are missing and bracts appear coloured and petaloid as in the Bougainvillea, one of the three whorls is missing: there are only two whorls of five organs instead of the three whorls of five organs described above. Because one whorl of the flower is obviously composed of stamens that bear functional pollen and the other whorl is composed of a brightly coloured set of organs that resemble petals one might conclude that the sepals are missing. But examination of positional relationships between the whorls reveals that the midline of each stamen is on the same line as the midline of the organs of the brightly coloured set. Thus, position tells us that the brightly coloured whorl represents a sepal whorl and that the sepals have assumed the function of the missing petals.

The receptacle Plants: From Cute to Carnivorous The peduncle is the stalk of a flower or an inflorescence. When a flower is borne singly, the internode between the receptacle and the bract (the last leaf, often modified and usually smaller than the other leaves) is the peduncle. When the flowers are borne in an inflorescence, the peduncle is the internode between the bract and the inflorescence; the internode between the receptacle of each flower and its underlying bracteole is called a pedicel . Thus, in inflorescences, bracteole is the equivalent of bract, and pedicel is the equivalent of peduncle. Connect with Britannica Facebook Twitter YouTube Instagram Pinterest Often the bract subtending an inflorescence is brightly coloured, as in the poinsettia (Euphorbia pulcherrima; Euphorbiaceae), or provides protection, as in the woody, boat-shaped bracts in many palms . Bracteoles in the inflorescence of Bougainvillea also are brightly coloured to attract pollinators (see photograph ).

In some angiosperms, the receptacle becomes fleshy; in the strawberry , for example, the receptacle is the fleshy edible part of the strawberry and, when eaten by small mammals and birds, aids in seed dispersal. In others, the peduncle or pedicel becomes fleshy; in the cashew (Anacardium occidentale; Anacardiaceae), for example, the pedicel is made into a drink in the Neotropics, and it also aids in fruit dispersal of the much smaller cashew nut. In cacti (e.g., prickly pear ), the fleshy part of the edible fruit forms from the receptacle and peduncle, and several internodes below that grow up and surround the carpels; this is why there are axillary buds in cacti (areoles) with spines on the fruit surface. The calyx The sepals (collectively called the calyx) most resemble leaves because of their generally green colour.

From their base and along most of their length, sepals remain either separate (aposepalous, or polysepalous) or marginally fused (synsepalous), forming a tube with terminal lobes or teeth (see photograph ). The number of calyx lobes equals the number of fused (connate) sepals. The sepals enclose and protect the unopened flower bud. The calyx is commonly persistent and evident when the fruit matures (e.g., persimmon , Diospyros virginiana ; Ebenaceae), in contrast to the more short-lived petals and stamens. Sepals may be brightly coloured and function as petals when true petals are missing—for example, the virgin’s bower ( Clematis ; Ranunculaceae) and the Bougainvillea . Petaloid sepals in this case differ from tepals because the first group of stamens are on the same radii as the sepals, indicating the absence of the petals, which would normally be positioned on alternating radii in the next floral whorl.

The corolla Editor Picks: Exploring 10 Types of Basketball Movies The petals composing the corolla are typically brightly coloured or white and attract insects and birds for pollination (see below Reproduction: Pollination ). The number of petals is usually the same as the number of sepals. Floral symmetry is defined by the petals ( Figure 13 ). When the petals of the corolla are of the same size and shape and when they are equidistant from each other, the flower has radial symmetry , and the flower is called regular or actinomorphic (e.g., buttercup , Ranunculus; Ranunculaceae). In regular flowers, any line drawn through the centre will divide the flower into two identical halves. When at least one petal of the corolla is different, the flower has bilateral symmetry and is called irregular or zygomorphic (e.g., violets, Viola ; Violaceae [see photograph ]). The petals of the corolla may be separate, or apopetalous, or marginally fused (fusion of like floral parts is called connation), or sympetalous, for all or part of their length.

When joined, they form a tubular corolla with terminal lobes (see photograph ). A tubular corolla may be present in regular flowers (e.g., blueberries , Vaccinium ; Ericaceae) or irregular flowers (e.g., sage , Salvia officinalis; Lamiaceae). Stamens are commonly united to a tubular corolla (fusion of two unlike floral parts is called adnation). A marginally fused (synsepalous) calyx, a marginally fused (sympetalous) corolla, and stamens may fuse to form a cuplike floral tube called a hypanthium that surrounds the carpels, as in cherries (Prunus; Rosaceae), for example. Fusion and reduction of flower parts are common and have occurred in many unrelated lineages. Many wind-pollinated angiosperms do not have petals, nor do they have floral parts modified as petals; examples of wind-pollinated species include the amaranth family (Amaranthaceae) and the birch family (Betulaceae).

Trending Topics Open Door policy Petals often bear nectaries that secrete sugar-containing compounds, and petals also produce fragrances to attract pollinators; the fragrance of a rose (Rosa; Rosaceae) is derived from the petals. Petals often develop a nectar-containing extension of the tubular corolla, called a spur. This may involve one petal, as in the larkspur (Delphinium), or all the petals, as in columbine (Aquilegia), both members of the family Ranunculaceae. The androecium Stamens (microsporophylls) are structures that produce pollen in terminal saclike structures ( microsporangia ) called anthers . The number of stamens comprised by the androecium is sometimes the same as the number of petals, but often the stamens are more numerous or fewer in number than the petals.

There are generally two pairs of spore-containing sacs (microsporangia) in a young stamen; during maturation the partition between the adjacent microsporangia of a pair breaks down so that there are only two pollen-containing sacs (one in each lobe of the anther) at the time the stamen releases the pollen. The least-modified stamens are similar to leaves, with the paired microsporangia located at or near the margins; an example is found in the magnolia family (Magnoliaceae). In more derived stamens, the blade has become modified into a slender stalk, the filament, with the microsporangia at or near the filament apex (the anther). The filaments are very often united with the corolla, but with the anthers either separate, as in primroses (Primula; Primulaceae), or united with each other to form a staminal tube that encloses the gynoecium, as in the mallow family ( Malvaceae ). In thistle (Cirsium; Asteraceae) and in other members of the sunflower family , the staminal tube is fused to the lower half of the corolla tube.

There are several trends in stamen modification. In many angiosperms, one or more of the stamens is modified and lacks functional anthers. In the most common modification, the filament is expanded to form a petallike blade called a staminode (in the same manner that a sepal forms a petallike blade in some flowers without true petals). The apparent petals in some angiosperm families, such as are found in many members of the pink family ( Caryophyllaceae ), are staminodial in origin. Wild roses have only five petals and many stamens; however, cultivated roses have been selected for the many apparent petals (but actually staminodes) and few functional stamens. In other cases, stamens have been modified into sterile nectaries involved in pollination. If flowers have a large number of stamens, then the stamens often occur in groups or clusters ( fascicles ; see photograph ), as in the myrtle family (Myrtaceae). The gynoecium The gynoecium is composed of carpels.

In more basal families (e.g., Magnoliaceae) the carpels are spirally arranged, and in more advanced families they tend to be arranged in a single whorl. Carpel number varies from one (e.g., bean or legume family [ Fabaceae ]) to many (e.g., buttercups or raspberries [Rubus]). At the base of a carpel is the ovary , within which develop one or more multicellular structures called ovules that each contain an egg. The upper part of the carpel, the stigma, receives the pollen. A slender stalk called the style often connects the ovary and stigma. The carpels may be separate (apocarpous) or fused together (syncarpous), with the individual carpel walls and cavities (locules) still present. Syncarpy may involve only the ovaries, leaving the styles and stigmas free, as is found in the wood sorrel ( Oxalis ), or it may involve both the ovaries and styles, leaving only the stigmas free, as in the waterleaf (Hydrophyllum).

The number of carpels in a syncarpous (or compound) ovary generally equals the number of locules (in some cases the inner carpel walls break down, leaving a single locule); in an orange or a grapefruit , for example, the juice sacs are actually trichomes that line the inner carpel walls of each cavity. The position of the gynoecium with respect to the petals, sepals, and stamens on the floral axis also characterizes the flower ( Figure 11 ). In hypogynous flowers , the perianth and stamens are attached to the receptacle below the gynoecium; the ovary is superior to these organs, and the remaining floral organs arise from below the point of origin of the carpel. In perigynous flowers , a hypanthium (a floral tube formed from the fusion of the stamens, petals, and sepals) is attached to the receptacle below the gynoecium and surrounds the ovary; the ovary is superior, and the free parts of the petals, sepals, and stamens are attached to the rim of the hypanthium.

In epigynous flowers , the hypanthium is fused to the gynoecium, and the free parts of the sepals, petals, and stamens appear to be attached to the top of the gynoecium, as in the apple (Malus; Rosaceae); the ovary is inferior, and the petals, sepals, and stamens appear to arise from the top of the ovary. Fruits Fertilization of an egg within a carpel by a compatible pollen grain results in seed development within the carpel. (Formation of fruit without the fertilization of an egg and subsequent seed development is called parthenocarpy .) A fruit is a ripened ovary (or compound ovary) and any other structure, usually the hypanthium, that ripens and forms a unit with it. This clearly separates a fruit from a vegetable , because a vegetable is derived only from vegetative (nonreproductive) organs.

Tomatoes, eggplants, and squashes are fruits, because they are derived from floral parts, whereas carrots, turnips (Brassica rapa), and beets are vegetables, because they are roots modified as storage organs in the same manner that potatoes, ginger (Zingiber officinale), and onions are modified stems. Simple fruits develop from a single carpel or from a compound ovary. Aggregate fruits consist of several separate carpels of one apocarpous gynoecium (e.g., raspberries where each unit is a single carpel). Multiple fruits consist of the gynoecia of more than one flower and represent a whole inflorescence, such as the fig and pineapple. Accessory fruits incorporate other flower parts in the development of the mature fruit; for example, the hypanthium is used in forming the pear (Pyrus; Rosaceae), and the receptacle becomes part of the prickly pear . The form, texture, and structure of fruits are varied (notably in simple fruits), but most fall within a few categories.

The fruit wall, or pericarp , is divided into three regions: the inner layer, or endocarp; the middle layer, or mesocarp; and the outer layer, or exocarp. These regions may be fleshy or dry (sclerified) or any combination of the two, but they are classified as either one or the other. The three main types of fleshy fruits are berries , drupes, and pomes. Berries are many-seeded simple fruits composed of one carpel or a syncarpous ovary. They are fleshy throughout, but the exocarp ranges in texture: a soft, thin exocarp, as in tomatoes (a berry); a leathery exocarp, as in oranges (a hesperidium); and a somewhat hard exocarp, as in pumpkins (a pepo). In drupes , or stone fruits, there is usually only one seed per carpel or locule. Drupes are fleshy fruits and consist of an inner stony or woody endocarp, which adheres to the seed (peaches, plums, and cherries).

The term druplet is used for each unit of aggregate fruit of this type (e.g., raspberries and blackberries). Pomes are fleshy fruits of the rose family (Rosaceae) in which an adnate hypanthium becomes fleshy (apples and pears). Simple dry fruits are either dehiscent or indehiscent . They are dehiscent if the pericarp splits open at maturity and releases the seeds, or indehiscent if the pericarp remains intact when the fruit is shed from the plant. The three principal types of dehiscent fruits are follicles , legumes , and capsules . Follicles and legumes are each derived from an ovary with a single carpel, and a capsule is derived from several united carpels. As the fruit matures, the pericarp dries and the fruit splits. Whereas follicles split along a single side of the fruit, such as in the milkweeds, columbines, and magnolias, legumes split along both sides, as in the bean family. Capsules have two or more carpels and split open to release their seeds in various ways.

They may open longitudinally to expose the seeds within each locule (cavity) or longitudinally along each septum between the locules, as in the agave (Agave; Agavaceae). Still others form an operculum (a lid) at the top of the ovary, as in the Brazil nut family (Lecythidaceae). Indehiscent fruits are derived from either single carpels or compound ovaries. Single carpel forms include the achene , the samara, and the caryopsis. Forms derived from a compound ovary include nuts and schizocarps. An achene is a fruit in which the single seed lies free in the cavity, attached only by a single point. The strawberry , for example, is really an aggregate fruit, and each “seed” is an achene. The samara is a winged achene and is found in the tree of heaven (Ailanthus altissima; Simaroubaceae) and ash (Fraxinus; Oleaceae). In the caryopsis , or grain, the seed adheres to the fruit wall (pericarp). The caryopsis is found among the cereal grasses, such as corn.

Nuts have a stony pericarp, and usually only a single seed in each carpel matures, as in acorns of oaks (Quercus; Fagaceae) and hazelnuts (Corylus avellana; Betulaceae). Schizocarps are fruits in which each carpel of a compound ovary splits apart to form two or more parts, each with a single seed . Schizocarps are found in the carrot family (Apiaceae). Winged schizocarps are found in maples.

Question: What name is given to the external set of floral leaves or sepals in a flower?
Answer: Calyx