Lecture on flower by Dr Chanchal Kumar Biswas

Lecture on flower by Dr Chanchal Kumar Biswas Department of Botany

THE FLOWER A flower is define as a modified reproductive shoot of determinant growth, consisting either only stamens (microsporophyll) or Carpel’s (megasporophylls) or both and may or may not be associated with accessory parts like sepal, petals to produce fruit and seeds.

Different term related to flower. Complete Flower: : A complete flower is a flower that has all four parts of the flower (sepals, petals, androecium and Gynoecium). Incomplete flower: 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).

Symmetry of flower • Actinomorphic (regular): Flowers that are radially symmetrical so that they are able to be bisected into similar halves in more than one vertical plane, forming mirror images. • Zygomorphic flower (irregular): Flowers that are bilaterally symmetrical so that they are able to be bisected into similar halves in only one plane, forming mirror images.

Cyclic(most of angiosperms): A flower whose parts are arranged in a whorl. Cyclic flowers are characteristic of most flowering plants, including those of the families Liliaceae, Caryophyllaceae, and Solanaceae. • Acyclic ( Eupomatia): A flowers whose parts are arranged in spirals rather than in whorls, as in magnoliales. • spirocyclic flower( Nymphaeaceae): It is flower where half of the members are arranged spirally and half of members arranged in whorl manner.

Pistillate and staminate flower • Unisexual or Imperfect flowers that bear stamens only are called staminate flowers or male flower. • Unisexual or Imperfect flowers that bear pistils only are called pistillate flowers or female flower.

• Monoecious plants are those in which both the staminate and pistillate flowers are borne on the same plant. Cucerbita. • Species in which the two imperfect flowers are borne separately in different plants are called dioecious. Borassus flabellifer. • Some plant bear male, female and bisexual flower are called polygamous flower. Eg Litchi sinensis.

Perianth • Perianth of a flower • The perianth is the outer envelope enclosing a flower and is made up of either: • an outer calyx and inner corolla; • a calyx or corolla; or • calyx and corolla combined and undifferentiated from one another. • The corolla of a flower is divided up into petals whereas the calyx is made up or sepals. – If the calyx and corolla are combined into one undifferentiated unit, then the individual parts are referred to as tepals.

Parts of typical flower • A flower consist of an axis known as thalamus, on which four different sets of floral parts are inserted. a. Thalamus: The thalamus is the receptacle or terminal part of the axis of a flower. Some times it is long , showing distinct internode.

Calyx: • In many Plant species, the calyx consists of green leaf-like structures, the sepals, which protect the delicate inner parts of the flower while it is developing and prevent it from desiccating. The sepals may be fused or free and symmetrical or assymetrical. In some plant families like. Liliaceae it is not possible to distinguish between sepal and petals and these structures are called tepals. •

Corolla • In many species, the corolla which consists of the whorl of petals, is the most obvious part of the flower. Some flowers have large, showy petals but in some families such as the grasses the petals have become very reduced. It is also free or fused and termed as polypetalous and gamopetalous.

AESTIVATION of floral parts. It is the mode of arrangement of accessory floral member ( sepal , petal & perianth ) with respect to one another in a flower bud. These are following types.

• Valvate: In this type, the margin of sepals or petals simply touch each other but not overlap. Mimosaceae. Twisted (contorted): In this case sepals or petals are arranged in such way that their one margin overlaps the margin of the next one and the other margin is overlapped by margin of another. Malvaceae Imbricate: In this case out of five accessory members one is purely internal, one is external and other three partly internal and partly external. E. g. Caesalppinaceae

Quincuncial: In this case out of five accessory member two is purely internal, two are external and one partly internal and partly external e. g. Apocynaveae. Vexillery: It is a type of imbricate aestivation, here out of five petals the odd posterior one (standard) is largest and outermost, it overlaps the two lateral petals (wings) and the lateral petals again in turn partly overlap the two smallest and innermost petals (keel).

Androecium: Depending on the numbers and arrangement of stamen, it is classified in to following groups. – Diplostemonous: stamens occurs in two whorl. And outer one is alternate with petals and consequently opposite to sepals. Cassia fistula – Obdiplostemonous: When stamens of outer whorl are opposite with petals and consequently alternate to sepals. Oxalis sp

• – Isostemony: When all stamens are in one whorl and are equal to the number of sepals and petals. – Tetradynamous: Stamens are six. Outer two are shorter and inner four are longer or vice versa (A 2+4) Cruciferae – Didynamous: Stamen four. Two are long and two are short. Labiatae

Union of stamen The union of stamens takes place either among themselves (cohesion) or with other whorls (adhesion). – Adhesion of stamens : Stamens may unite with other floral whorls like Perianth, petals or gynoecium. Based on the floral organ involved in the union with stamens, the adhesion may be of the following types :

Adhesion of stamens • Epiphyllous : Stamens unite with perianth. e. g. , Asperagus. • Epipetalous : Stamens unite with petals. e. g. , Datura. • Gynandrous : Stamens unite with gynoecium. It is also called gynandrium or gynostegium. e. g. , Calotropis.

Cohesion of Stamens Usually three types of cohesion among stamens occur. They are : 1. Adelphous: Anthers remain free and filaments are united. Adelphous condition can be (a) Monoadelphous—United to form 1 bundle, e. g. , China rose (b)Diadelphous—United to form 2 bundles, e. g. , Pea (c)(c) Polyadelphous— United into more than two bundles, e. g. , Lemon

2. Syngenesious: Filaments free and anthers united, e. g. , Sunflower. 3. Synandrous: Stamens fused all through their length, e. g. , Cucurbita

Attachment of anther to the filament • Innate or Basifixed: When the filament is firmly attached to the base of the anther. Solanum sp • Adnate: When filament running the whole length of the anther from the base to apex. Michelia sp • Dorsifixed: When the filament attached to the back of anther. Bauhinia variegate. • Versatile: Filament attached to the back of anther at a point only , so that the later can swing freely. Graminae

Dehiscence pattern of Stamen • (i) Porous: Pollens released through pores, e. g. , Brinjal, • Potato • (ii) Longitudinal: Pollens released through the longitudinal • slit of another lobes, e. g. , China rose, Cotton

Gynoecium. o Gynoecium : The gynoecium or pistil is the fourth essential whorl of the flower and may be made up of one or more carpels (megasporophylls). o A carpel has three distinct part, namely ovary, style and stigma. The lower most swollen fertile part of the carpel is the ovary. It encloses ovules. Above the ovary elongated thread like structure attached to the apex of the ovary, the style. The style end with a round, sticky stigma. o A sterile pistil is known pistillode. The number of carpels in a gynoecium vary in different flowers. Accordingly the gynoecium may be described as follows :

– Monocarpellary : It is a ovary with a single carpel, e. g. , Bean. – Bicarpellary : It is presence of two carpels in a ovary, e. g. , Solanum. – Tricarpellary : It is presence of three carpels, e. g. , Cocos. – Tetracarpellary : It is presence of four carpels, e. g. , Cotton. • Pentacarpellary : It is presence of five carpels, e. g. , Hibiscus. • Multicarpellary : It is presence of many carpels, e. g. , Annona.

Cohesion of carpel. If number of carpels is more than one, they may be • (i) Apocarpous: Carpels are free. Each carpel has its own style and stigma, e. g. , Rose. • (ii) Syncarpous: Carpels are united, e. g. , Lady’s finger, Tomato

The ovary encloses one to many chambers called the locules. Usually the number of locules in a syncarpous ovary corresponds to the number of carpels. Sometimes, the number of locules may be doubled. e. g. , in Datura, the gynoecium is bicarpellary syncarpous with four locules in the ovary. Based on the number of locules, the ovary may be described as follows : Unilocular : Ovary with one locule. e. g. , Dolichos. Bilocular : Ovary with two locules. e. g. , Solanum. Trilocular : Ovary with three locules. e. g. , Allium. Tetralocular : Ovary with four locules. e. g. , Datura. Pentalocular : Ovary with five locules. e. g. , Hibiscus. Multilocular : Ovary with many locules. e. g. , Abutilon.

Placentation refers to the arrangement of ovules within the ovary. Ovules are attached to ovarian walls through special structures called as placenta. Marginal: The placenta forms a ridge along the ventral suture of the ovary and the ovules are borne on this ridge, e. g. , Pea Axile: The ovary is partitioned into several chambers or locules and the placentae are borne along the septa of the ovary, e. g. , Tomato, China rose Parietal: The ovules develop on the inner wall of the ovary or on peripheral part. Ovary unilocular but in some cases becomes two chambered due to formation of a false septum, e. g. , Mustard

(iv) Free central: Ovules are borne on the central axis and septa are absent, e. g. , Carnation, Chilly (v) Basal: Placenta develops at the base of the ovary, e. g. , Sunflower.

Style The stalk like structure present above the ovary is called the style. The style may be long (Datura) or short (grasses) or absent (Papaver). In the family umbelliferae (Apiaceae) the base of the style is swollen and forms a structure called stylopodium. There are three types of styles as described below :

Kinds of style Terminal style : If the style arises from terminal part of the ovary, it is called terminal style, e. g. , Datura, Hibiscus and Solanum. Lateral style : If the style arises from one side of the ovary, it is called lateral style, e. g. , mango. Gynobasic style : If the style arises from the base of the ovary it is called gynobasic style, e. g. , Ocimum, Salvia.

Stigma The terminal pollen receptive portion of the style is called the stigma. It receptive pollen grain during pollination. Usually the lobes of the stigma equal to the number of carpels. The stigma may be unifid, bifid, trifid, tetrafid, pentafid or multifid.

• Capitate : Round stigma. e. g. , Hibiscus. • Forked : Divided stigma. e. g. , Tridex. • Feathery : Brush like stigma. e. g. , Grasses.

FLORAL FORMULA • Once the description of the plant is completed, major characters of the flower are written in a special method where few signs and letters are used. • This formula is useful in knowing major characters of a flower at a glance. In this method characters of bracts, symmetry sex, calyx, corolla, (or parianth), androecium and gynoecium are denoted in this order. Some of the commonly used denotations are given below.

• Bracts and Epicalyx; Br……… Bracteate Ebr……. . . Ebracteate Brl………Bracteolate E………. . . Epicalyx • Symetry …. Actinomorphic or . Zygomorphic • Sex; …. . Staminate flower …. . Pistillate flower …. Hermaphrodite • Calyx; K…. Calyx K 4……Four free sepals K(4) …. Four fused sepals • Corolla; C……Corolla C 4…. . Four free petals C(4)…. Four fused petals • Perianth; P……. . Perianth P 5……. Five free tepals P(5)……Five fused tepals P 3+3…. . Six tepals in two whorls

• Androecium; A………Androecium A 5……. . Five free stamens A(5)……Five fused stamen. A 5+5…. . Ten stamen in two whorl of five each A 0…………Stamens absent. A ……………. Stamen indefinite in number. C A… . . Stamens epipetalous P A…… Staens epiphyllous • Gynoecium; G………. . Gynoecium G 3………. three free carpels G(3)………three fused carpels. G 0………. . Carpels absent G_(2)……. . two fused carpel, overy superior G(3) ………Three fused carpel, semi inferior overy. G (2)………. Two fused carpel, inferior overy.

Floral diagram • Floral Diagram • The floral diagram is a ideal ground plan of a flower. It is a method in which many of the characteristics of its parts and symmetry can be expressed in a graphic form.

Insertion of floral leaves It means the structure of thalamus and the consequent position and insertion of calyx, corolla androecium in relation to the pistil • Hypogynous: • A flower in which the overy is superior and all other floral organs are situated below its level. Michelia champaca

• Perigynous: • The thalamus is flat or concave and the floral organs arising from around the ovary and not beneath it. Papilionaceae

• Epigynous: • The thalamus is concave and the floral member are arise above the pistil. E. g. Compositae

Insertion of floral leaves

Flower is Modified shoot • Morphologically a flower is a modified shoot. The elongated axis (internodes) of a vegetative shoot is reduced into a horizontal disc, the receptacle. Floral leaves are arranged on the receptacle in different whorls. • By the Following fact it can be established that the flower is modified shoot.

1. Axis nature of the thalamus: Flower consists of a thalamus or torus, which is very much like an axis in some cases. • a. The axis bears modified floral leaves such as sepals, petals, stamens and carpels. Generally the axis in a flower consist of short or suppressed Internodes and nodes. But it is not the normal rule; the axis is long in some flower e. g. Gynandropsis gynandra ( Capparidaceae ), Passiflora suberosa ( Passifloraceae) etc. The internode of the thallamus between corolla androecium (andophore) and between androecium and gynoecium (gynoephore) become enlarged with same whorled arrangement of stamens and carpels respectively. ; so here thalamus behaves like a axile.

• Gynandropsis gynandra • Passiflora superba

• b. Normally the growth of the thalamus is checked by the carpels but in some thalamus has been found to undergo further upward growth having green stem and small foliage leaves beyond the gynoecium, this phenomenon also support that flower is a modified shoot. E. g. Rosa sp, Pyrus sp This phenomenon is known as monstrous development.

• c. In some cases the carpel bearing region of the thalamus elongate like the stem giving rise to an aggregate fruit. E. g. Polyalthia longifolia Michalia champaca

2. Leaf nature of floral member: This is evident by many plant member Following are some example. a. In many cases the sepal are leaf like with veins and petals like pigments e. g Mussanda frondosa

b. In some cases the floral leaves are both verticillately and spirally arranged On long thalamus but in majority of flowers the floral phyllotaxy is whorled eg Michalia champaca c. The leaf nature is also proved by the gradual transition of sepals to petals and petals to stamen and so on as in found in Nymphaea sp

D. Carpel is also leafy in nature can be proved by on examination of single carpel of Pisum sativum in which it is folded along its midrib to form a chamber.

3. Homology of floral buds Floral buds like vegetative buds may be metamorphosed bulbils e. g. viviparous bulbils of Agava sp. Development and position of vegetative bud are also like those of floral buds i. e. axillary and terminal.