Diversity of flowers - e
Transcription
Diversity of flowers - e
5 Diversity of flowers By the end of this chapter, you will be competent to... w identify the morphological diversity of flowers. w describe a flower by using scientific conventions. w investigate the patterns of inflorescences. w analyse the structure of fruits. w use the diversity of life time of plants to fulfil the day - today pursuits. 73 For free distribution 5.1 Morphological diversity of flowers The plants which bear flowers are known as flowering plants. Plants which do not bear flowers are categorised as non-flowering plants. e.g. mosses, ferns, algae and conifers. Majority of the plants in the plant kingdom produce flowers. Though flowers are generally considered as structures which are colourful, beautiful and consist of petals, small flowers which are not noticeable at first glance are also found in herbs and grass varieties. Flowering plants can be divided into two categories as dicotyledons and monocotyledons. Flowers are specially structured for reproduction. A Flower can be considered as a special structure designed to determine the survival and existence of its species. 5.1.1 Parts of a flower and their arrangement A flower is a modified shoot. That is instead of a bud grows and produces a shoot, it gets modified to produce a flower. The flower is fixed on to the stem by a stalk. The top of the stalk is expanded to form a torus or thalamus. All the parts of the flower is arranged in four whorls on the torus. In a flower four types of flower parts can be identified. They are calyx, corolla, androecium and gynaecium (from outer ring to inner). anther filament } stamen Petals (corolla) Sepals (calyx) Stigma Style Ovary thalamus (torus) pedicel (stalk) Fig 5.1.1 Main parts of a flower 74 For free distribution } gynaecium Calyx Calyx is a cup shaped structure. It is found at the bottom of all the other parts. It is the outer most whorl of a flower. It consists of sepals. Sepals are similar to small green leaves. Colurful sepals can be seen in some flowers. Function of the calyx is the protection of the tender flower bud. Photosynthesis takes place in green coloured sepals. Colourful sepals are important to attract insects for pollination. (Fig 5.1.2 and 5.1.3) Rose Sesbenia Tribulus Fig 5.1.2 - Flowers with green sepals Muntingia Species of Musandas Fig 5.1.3 - Flowers with colourful sepals Do you know In some flowers a whorl of floral leaves can be seen outside the calyx. It is known as epicalyx Example:- Shoe flower Cotton flower Shoe flower Cotton flower calyx and epicalyx 75 For free distribution Do you know? In some flowers the sepals do not fall off even after the fruits are produced. Example :- Mangoosteen Guava Rose apple Guava Mangoosteen Fruits with persistent sepals Corolla Within the calyx are the whorl of floral leaves called petals, together forming the corolla. It is the most beautiful and attractive part of most flowers. The corolla protects the internal parts of the flower and also helps to attract insects for pollination. The corolla is colourful in majority of flowers which are pollinated by insects. Corolla shows diversity in colour and shape. Examples:- Fig 5.1.4 Clitoria Wrightia Catharanthus Shoe flower Orchid Fig 5.1.4 - Diversity of Corolla in shape and colour 76 For free distribution Alstonia In most of the flowers which bloom during the night, the corolla is white in colour, and the flowers are scented. This is also important to attract insects for pollination. Examples:-Fig 5.1.5 Coral jasmine (Sepalika) Kadupul Fig 5.1.5 - Flowers bloom during the night Getapichcha Androecium Androecium is the male part of a flower. It is the whorl of floral leaves found inside the corolla. Andreoecium consists of stamens. A stamen consists of the anther and the filament. The function of the androecium is to produce pollen grains for reproduction. Structure of Androecium in different Flowers Stamens of flowers can be independent or connected to the petals. e.g: Fig 5.1.6 Passion fruit Torenia Shoe flower Gloriosa Brassica Calotropis Fig 5.1.6 - Situation of anthers in different flowers 77 For free distribution Gynoecium or Pistil stigma Gynoecium or pistil is the female part of a flower, It is the innermost part of a flower. It consists of three parts namely stigma, style and ovary. The stigma is situated at the top and the ovary is situated at the base. The style is a tube like structure which connects the stigma and the ovary. Ovules can be seen in the ovary. After pollination and fertilization the ovary becomes the fruit and the ovules become seeds. style ovary Fig 5.1.7 - gynoecium of a flower Unisexual and Bisexual Flowers If both the gynoecium (pistil) and the androecium are present in a flower it is called a bisexual flower. Examples:- Hibiscus (Shoe flower) , Sesbenia, Lotus, Blue Lily Shoe flower Cannon ball tree Fig 5.1.8 - Bisexual Flowers Caesalpinia In some flowers only one of these parts is present. Such flowers are called unisexual flowers. Example:- Coconut, Maize staminate flower pistilate flower a - staminate flowers b - pistilate flowers Fig 5.1.10 - coconut (In coconut, both staminate and pistilate Fig 5.1.9 zia - maize flowers present in the same in florescense) 78 For free distribution Flowers which consist of only the gynoecium (pistil) are called pistilate flowers while flowers consist of only the androecium are called staminate flowers. Activity - 5.1.1 Divide your class into four groups. Select 10 kinds of flowers which can be easily found from your surrounding. Observe and identify the diversity in the calyx, corolla, androecium and gynoecium Symmetry of flowers Actinomorphic Flowers If a flower can be divided into two similar halves by cutting vertically through any one of its axis which passes through the centre, such flowers are known as radially symmetrical flowers or an actinomorphic flowers. Examples:- Shoe flowers, Jam, Temple flowers, Hendirikka (Mirabilis) Wrightia, Kaduru, Pupmpkin Catharanthus Pumpkin Shoe flower Kaduru Mirabilis Fig. 5.1.11 – Actinomarphic flowers Temple flower Wrighita Zygomorphic flowers Some flowers can be divided into two similar halves by cutting along only one symmetrical axis. These flowers are known as bilaterally symmetrical flowers or zygomorphic flowers. 79 For free distribution Sesbenia Thunbergia Orchid Leucus zeylaniea Caesalpinia Salvia Crotolaria Fig 5.1.12 - zygomarphic flowers Asymmetrical flowers Some flowers cannot be divided into two similar halves by cutting along any axix. These flowers are known as irregular or asymmetrical flowers. Examples:- Cannas, Cactus Species of Cactus Species of Cactus Fig 5.1.13 Irregular flowers Species of Canna Activity - 5.1.2 Bring 20 kinds of flowers which can be easily found from your surrounding to the school. Observe its symmetry and group them as actinomophic, zygomorphic and asymmetrical flowers. 80 For free distribution 5.2 Structure of flowers There are some standard methods to describe the structure of flowers. They are 1. Whole flower and half flower 2. floral diagram 3. floral formula Whole Flower By observing a flower externally we can study the structure of the flower. To observe the colour, the nature, its parts and their position in the flower by the naked eye one has to observe a whole flower. Half Flower To observe the parts of a flower more clearly we can separate a flower into two similar halves through a symmetrical axis of the flower. Fig - 5.2.1 – whole flower Because some parts which cannot be seen by observing the flower externally, can be clearly seen in a half flower. (fig 5.2.2) Therefore a half flower is used to describe the structure of a flower. Half flower can be depicted by a line diagram. Fig 5.2.2 – a half flower 81 For free distribution Floral Diagram A transverse section drawn so that all the parts of the flower are in the same level is called a floral diagram. This is similar to a diagram of a flower drawn as seen from the top. To draw a ksm;%h bract floral diagram the main axis of the tree should main axis placed to the anterior side and the bract should of the tree placed to the posterior side. a b a) Position of a flower in the tree Fig 5.2.3 - Position of a Flower and b) Floral diagram of a flower Floral diagram Floral Formula A formula written using standard symbols to describe the morphological features of a flower is known as floral formula. Example :- floral formula of a shoe flower K(5) C 5 Aα G (5) The symmetry of the flower is depicted by the first symbol. Symbol Symmetry - Actinomorphic - Zygomorphic According to this, the symmetry of a shoe flower is actinomorphic. The second symbol depicts the sex of the flower - staminate pistilate bisexual According to this, the shoe flower is bisexual The third symbol ‘K’ depicts the calyx. The numeral at the bottom shows the number of sepals. If the numeral is written within brackets it depicts that the sepals are connected. 82 For free distribution According to this, the shoe flower has 5 connected sepals. The fourth symbol ‘C’ depicts the corolla The numeral at the bottom shows the number of petals in the . If the numeral is written within brackets it indicates that the petals are fused. According to this, the corolla of the shoe flower has five independent petals. The fifth symbol ‘A’ depicts the androecium. The numeral at the bottom shows the number of stamens. If the numeral is written within brackets the stamens are fused. According to this, the number of stamens in the androecium cannot be counted easily. C A All the filaments of the stamens of a shoe flower are connected to make the staminal tube. The sixth symbol ‘G’ depicts the gynaecium. The numeral at the bottom shows the number of parts in the pistil. If the numeral is written within brackets, it depicts that these parts are connected to each other. The situation of gynaecium is depicted by drawing a line over or below its symbol. If it is situated above all the other parts of the flower, the short line should be drawn below the letter ‘G’. If the ovary is situated below the other parts of the flower, the short line should be drawn above the letter ‘G’. According to this, the gynaecium of the shoe flower consists of five parts and they are connected. The gynaecium is situated above all the other parts. Now let us consider the floral formula of two other kinds of flowers. Sesbenia K(5) C(2)+2+1 A(9) +1 G(1) Ipomea K5 C(5) A5 G(2) Assignment 1 Try to describe the features of the Sesbenia and Ipomea flowers by studying their floral formula. 83 For free distribution 5.3 Inflorescence Leaves and flowers are situated on the tree trunks according to a certain way. Some flowers are situated alone while some are situated as groups on a central axis. When flowers are situated as groups on a central axis it is called an inflorescence. The main axis of an inflorescence is the peduncle while the stalk of each flower is called a pedicel. Inflorescence can be divided into two categories according to the way in which flowers are arranged on the main axis. 1. Racemose Inflorescence 2. Cymose Inflorescence Fig - 5.3.1- an inflorescene 5.3.1 Racemose inflorescences Terminal buds of racemose inflorescences continuously grow for some time and flowers gradually start growing from the bottom of the axillary bud towards the top of it. Matured flowers can be seen at the bottom of the inflorescence while tender flowers can be seen on the top. Flowers start blooming from the bottom of the inflorescence and continue upwards towards the top. Raceme These flowers consist of pedicels. Examples:- Crotolaria, Orchid, Ehela (Cassia fistula) Ehela (Cassia fistula) Orchid Fig - 5.3.2- Racemose inflorescence 84 For free distribution Spike This is similar in all aspects to a raceme, but the flowers are sessile. Examples Amaranthus, Stachetophyta Spadix Cat's tail (Acalypha) Stachetophyta (Balunakuta) Fig - 5.3.3- Spike Amaranthus (Tampala) The flowers are sessile. These flowers are attached to a fleshy, thick central axis. A leaf like structure called spathe can be seen at the bottom of the central axis. This is an adaptation of the bract. Before the inflorescene bloom it is completely covered by the spathe. Examples:- Anthurium, Alocasia inflorescence sheath Anthurium, Alocasia (Gahala) Corymb Anthurium species Fig - 5.3.4 Spadix As the stalks of the basal flowers are longer than the stalks of the terminal flowers, they seem to be in one level. Examples – Caesalpinia pulcherima, Some Cassia species Thora (Cassia) Caesalpinia pulcherima (Monera mal) Fig - 5.3.5- Corymb 85 For free distribution Umbel All the flowers appear in the same level. Matured flowers are situated outside the inflorescence while tender flowers are seen at the centre of the inflorescence. Examples – Red onion, Crinum, Lantana, Isora Capitulum Lantana Fig - 5.3.6 - Umbel Crinum The flowers are sessile. A disc like structure is created as a result of the flat central axis. The flowers are seen on this disc like structure. Here too the tender flowers are situated at the centre of the inflorescence while matured flowers are seen in the outer part of it. Examples – Tridax, Zenia, Monarakudumbiya, Sun flower Sun flower Zenia Fig 5.3.7 - Capitulum Tridax 5.3.2 Cymose Inflorescenses There are more than one axis in cymose inflorescences. The main axis ends with a flower. In a cymose inflorescene tender flowers can be seen at the bottom while the matured flowers are at the top. Flowers bloom from the top towards the bottom according to the centrifugal method. Cymose inflorescences can be further classified into several types. Simple cyme There are only three flowers in a Simple cymose inflorescene. Example:- Some Jasminum species. 86 For free distribution A species of 'Pichcha' Fig - 5.3.8 - Simple cyme Dichasial cyme A dichasial cyme can be formed due to the continuous branching of lateral branches. Examples:- Begonia, Girithilla Begonia Fig - 5.3.9 - Dichasial cyme Girithilla Helicoid cyme Lateral branches always grow on one side of the central axis. As a result a curved inflorescence is formed. Examples :- Brinjal, ' Ethhonda' Brinjal Scorpoid cyme 'Ethhonda' Fig - 5.3.10 - Helicoid cyme Lateral branches grow on the either sides of the central axis. Here monochasiums formed by inhibiting the lateral branches side by side. Examples:- Leucus zelaynica, 'Uruhonda ' Though the inflorescences are classified as racemose and cymose, you may find other types of inflorescences which do not belong to any of these catagories . Leucus zelaynica Fig - 5.3.10 - Helicoid cyme Assignment - 1 Make a small booklet about inflorescences including examples for each type of inflorscene you studied in this chapter. 87 For free distribution 5.4 Diversity of fruits Fruits A fruit is an ovary developed and grown larger after stimulated by pollination. After pollination the ovary becomes the fruit while the ovules become the seeds. Fruits are mainly of three types. They are 1. Simple fruits 2. Aggregate fruits 3. Composite fruits / Multiple fruits 5.4.1. Simple fruits Simple fruits can be divided into two, according to the nature of pericarp. They are 1. Fleshy (Succulent ) fruits 2. Dry fruits Simple Fleshy fruits Pericarp of this fruits are fleshy or fibrous. Fleshy fruits are of many types. Mango Coconut Tomato Guava Apple Orange Fig 5.4.1 - Simple Fleshy fruits Pumpkin 88 For free distribution Simple dry fruits The fruits which are having a dry nature at the time of seed dispersal are simple dry fruits. Example - Beans, Olinda, Calotropis, Ladies fingers. Sun flower, Paddy, maize, Wheat, Vernonia, Dipterocarpus, cashew nuts, Anona Mimosa and castor. Calotropis beans Paddy Cashew Ladies finger Maize Fig 5.4.1 - Simple dry fruits Wheat Popy 5.4.2 Aggregate fruits An aggregate fruit is produced by a single flower with an apocarpous ovary. Fruitlets develop one by one gradually. A fruit of this type is a collection of fruitlets. Anona Strawberry Fig 5.4.3 - Aggregate fruits Anona specias 89 For free distribution 5.4.3 Composite fruits If a simple fruit originates from an inflorescene it is known as a composite fruit (multiple fruit). Example :- Pineapple, jak, mulberry, Ficus (Bo, Nuga, Attikka), Bread-fruit. Pineapple jak Fig 5.4.4 Composite fruits bread-fruit 5.5 Dispersal of fruits and seeds A fruit is produced in a tree for the purpose of reproduction to produce a new plant. A new plant is produced by the germination of seeds in a fruit. A single tree produces a large number of fruits at a time. Therefore a tree produces a large number of fruits in a number of seasons throughout its life time. The aim of producing fruits is to ensure the existence of the species. All these seeds may not get a chance to produce new plants.Only a few of them are able to produce new plants. If all the seeds get germinated near the mother plant they will rarely grow into healthy, matured plants. The probability of these seeds growing into healthy, matured plants is less. This is due to the competition for space, water, air, nutrients etc. Sometimes when a certain species of plant is limited to one area they can get destroyed by natural disasters. So dispersal of fruits and seeds is essential for the survival of the species. There are 4 ways in which fruits and seeds are dispersed. They are : 1. By wind 2. By water 3. By animals and 4. By explosive mechanisms 90 For free distribution Fruits that use explosive mechanisms for dispersal, dispersal agents are the seeds. The fruits that depend on other factors such as wind, water and animals for dispersal, dispersal agent can be a whole fruit or a part of a fruit. Fruits and seeds show various adaptations for dispersal. 5.5.1 Dispersal by wind A large number of fruits and seeds are produced in trees where the dispersal of fruits and seeds is caused by wind. Sometimes these fruits and seeds may land in places which are not suitable for the germination, causing a wastage. That is the reason for producing a large number of fruits and seeds. Some of the adaptations seen in fruits and seeds for dispersal by wind is stated below. 1. Light weighted and small seeds examples - Orchid 2. Having Structures such as wings Examples – Dipterocarpus, Shorea, Pterocarpus, Tecoma 3. Having hair like structures Examples – Vernonia, Nerium, Calatropis, Cotton Pterocarpus ' Thotila ' Dipterocarpus Calotropis Fig 5.5.1 - Fruits and seeds dispearsed by wind Tecoma Cotton 91 For free distribution 5.5.2 Dispersal by water In plants growing in or around water, dispersal of fruits and seeds is occured by water. There are various adaptations in these seeds and fruits to float on water. Some of them are, presence of air spaces, holes, having a fibrous covering and being impermeable to water. Examples :- Calophyllum, Terminalia, ' Kaduru ', Lotus, Coconut, Arecanut Rhizophora(Kadol), Water lily, Blue lily Arecanut Calophyllum 5.5.3 Coconut Terminalia Kaduru Fig 5.5.2 - Fruits and Seeds dispersed by water Lotus Dispersal by animals Seeds that are dispersed by animals show various adaptations. 1. Having a fleshy part which can be consumed by animals Fruits or seeds which can be consumed by animals and dispersed in various places. Most of the time the seed is thrown away after eating the fleshy part. Examples:- papaw, mango, dates, orange, avacardo In some instances the seed too is consumed with the fruit. Afterwards the seed will come out of the body with the waste matters. When the seed is passing through the digestive system no harm will be caused to the seed. After coming out of the body, it will get germinated when it finds a suitable place. Examples:- guava, tomato, chillie 92 For free distribution 2. Having appendages to cling on to animals Examples:- Love grass, 'Karal heba', 'Nerenchi', Tiger claws (Nagadarana) Seeds of some fruits are visible as small insects to trick the animals. So the birds carry them off and drop them in another place. Through this method too the seeds get dispersed. Examples:- Castor, 'Madatiya' , 'Crabs eyes' (olinda) Tomato Tiger claws 5.5.4 Papaw Guava Chillie Castor ' Nerenchi ' Fig 5.5.3 - Fruits and seeds dispearsed by animals Dispersal by explosive mechanisms Due to a change caused in pericarp the fruits burst and the seeds are thrown away to a distance. Examples – Balsom, ' Madatiya ' , ' Crabs eyes ' Bauhenia" Rubber Rubber Balsam Bauhenia Fig 5.5.4 - Fruits and seeds dispearsed by explosion Madatiya The method of dispersal by explosion is not very successful as the seeds are not thrown far away. 93 For free distribution 5.6 Diversity in plant habit Grouping plants according to its life span Plants show a diversity in the life span too. They can be divided into 3 groups. 1. Annuals 2. Biennials 3. Perennials 5.6.1 Annuals The plants which completes its life span and die within one season or one year are known as annuals. Example :- Grains like paddy and wheat, vegetables like cucumber and tomato. Paddy Maize Fig 5.6.1. Some annual plants Tomato The growth of these plants occur during the early stage. Reproduction occurs during the last stage after the growth stops. They produce flowers, fruits and seeds and die at the end of a season or a year. These plants spend the unfavourable season as seeds. 5.6.2 Biennials Plants which completes its life cycle and die within two years or two seasons are known as biennials. Growth continues upto two years and at the end of the second year they die after producing flowers, fruits and seeds. Example:- Vegetables like cabbage, carrot and beet- root. The food produced during the growing stage of the first year is stored in storage organs like underground roots. Flowers are not produced at the end of the first growing stage. At the beginning of the unfavourable season the aerial parts of the plant die and the undergroond roots and the terminal bud remains inactive (dormant). Again when the favourable season begins the underground roots and the terminal buds begin their work, start growing and produce a new shoot. These plants produce flowers, fruits, seeds at the end of the second season of growth and die. 94 For free distribution These plants spend one unfavourable season as underground stems and terminal buds, and spend the other unfavourable season as seeds. Carrot Beet root Fig 5.6.2 Some biennial plants Cabbage 5.6.3 Perennials Plants which live for more than two years are known as perennials. These plants are adapted to survive even during the unfavourable seasons. Surviving these unfavourable seasons using various methods is known as perennation. Perennation is a characteristic of perennials. There are different adaptations in plants for perennation. Some of them are given below. 1. Live underground and being inactive. 2. Have inactive (dormant) buds 3. Covered with a bark containing non living tissues. 4. Leaves fall off to avoid transpiration during dry seasons. Perennials are mainly of two types. 1. Herbaceous perennials 2. Woody perennials Herbaceous perennials These plants live as herbs. They have underground stems. Perennation is done as underground stems. Examples:- grass, ginger, colocasia, onion 95 For free distribution Colocasia Ginger Fig 5.6.3 Some herbaceous perennials Crysanthimum Woody perennials Shrubs and trees are included. The aerial parts continue growing for some years. Reproduction occurs after growth. After that flowers and fruits are produced untill the end of their life span. Having a bark with phellem, having inactive or dormant buds and leaves falling off are some adaptations for perennation. Mango Jak Fig 5.6.4 Some woody perennials Coconut 5.6.4 Uses of plants to humans Annuals Most of the plants taken as food by humans and animals fall under this category. Paddy, wheat, maize which are considered as main food items of humans are annuals. Leafy vegetables and medicinal plants too belong to this category. These plants complete their life span at the end of a year or a season and the fruits, seeds and other parts are taken into use by humans and animals. Biennials These plants too are taken as food by humans. 96 For free distribution Perennials These plants are used as food and for many other needs. Examples 1. As food items (jak, bread fruit) 2. As fruits (Mango, jambu, avacardo, rambutan). 3. To make drinks (tea, coffee, cocoa) 5. As medicines (Aralu, Bulu, Nelli) 6. To obtain oils (coconut, Citronella, castor) 7. To obtain fibres (cotton, jute& 8. To produce useful objects (rubber) 9. As timber (Satinwood, halmilla, teak, nedun) 10. For shade (Mara) 11. For beauty (Plumeria, roses) Assignment - 1 Prepare a list of plants found in your home - garden or school garden. Classify and tabulate them as annuals, biennials and perennials. Exercises 1. Select the correct answer for the statements given below from the words within brackets. (calyx, receptacle, umbel, androecium, floral formula, spadix, corolla, gynaecium) i. The most outstanding colourful part of a flower ii. The whorl that protects the tender flower iii. The male part of a flower iv. The female part of a flower v. Use to describe the structure of a flower vi. A racemose inflorescene covered by a structure (sheath) called spathe vii. All the parts of a flower situated in whorls on this structure 2. i Fruits and seeds get a chance to germinate far away from the mother plant by various dispersal methods. Give two reasons for the necessity of such a process. ii What is the dispersal method of the seed given in the picture according to its adaptations. iii Write two characteristic features of the above mentioned seed to be dispersed by the method you mentioned. 97 For free distribution 3. Plants are classified into three categories according to the plant habbit. They can be classified into three categories according to the life span also. i What are the three categories of plants according to their life span ? ii Classify the plants which are giving the following products according to the above classification,. tomato, bread fruit, mango, onion, carrot, cucumber, papaw, beet-root, zea maize, jak, anona, cabbage. iii Classify and tabulate the fruits mentioned below as simple, aggregate, and multiple composite. tomato, cucumber, bread fruit, mango, jak, anona. 4. Floral formula are used to describe the morphological features of a flower. Mentioned below is a floral formula of an imaginary flower. Study it carefully and fill in the blanks. (Please copy this paragraph into your note book before you do the exercise) K5 C(5) A5 G 2 The flower depicted by this floral formula is ........................... (actinomorphic/ zygomorphic). That is a ..........(unisexual / bisexual) flower.This flower has five ........... (free/ combined) petals. The number of stamens are ................... (five / two). Gynacium has two chambers. The gynaecium is situated ................... (below/ above) the other parts of the flower. 98 For free distribution