Morphology of Flowering Plants
- Flower is a specialized condensed shoot of an angiospermic plant is which the shoot apical meristem gets transformed into floral meristem for carrying out sexual reproduction through progressive specialization of leaves into floral appendages.
- The lower inter node forms the pedicel (or) stalk of the flower which may bear 2 bracteoles. The region where internodes are condensed, forms the broad base of the flower and lies at the tip of pedicel is called thalamus / Receptacle / Torus.
- Four types of floral organs are (i) Sepals (green) (ii) Petals (coloured other than green) (iii) Stamen and (iv) Carpels
- Sepals and petals are non - essential (or) necessary floral organs, where as stamens and carpels are essential organs which take part in reproduction.
- Floral organs are borne on the thalamus either in spirals (acyclic / spiral) (Eg : Magnolia), Whorls (cyclic Eg. Petunia) or with some organs in spirals and other organs in whorls (Spirocyclic / hemicyclic eg : Ranunculus)
- A flower having all the four types of floral organs is known as complete. The absence of any one or more of the floral organs makes the flower incomplete.
- A flower having both the essential organs is described as perfect, bisexual, hermaphrodite (or) bisexual. It is imperfect (or) uni sexual if only one of the 2 essential floral organs is present.
- When both the essential organs are absent, the flower is called Neuter.
- Both the types of uni sexual flowers may be present on the same plant and such plants are called monoecious eg : Maize, castor, cucurbits, Acalypha.
- When a plant bears only one type of uni sexual flowers, it is termed as dioecious eg : Date palm, Mulberry.
- The arrangement of the floral organs around the axis of a flower is known as floral symmetry.
⇒ Actinomorphic (radial symmetry) - Eg : Mustard, Datura, China rose, chilli.
⇒ Median zygomorphic - Eg: Pea, bean, larkspur, gulmohar, cassia
⇒ Laterally zygomorphic - Eg: Fumaria.
- If the floral parts of each series of a flower are similar in size, shape, colour and origin, the flower is said to be regular. A flower which shows any irregularity in any type of its floral organs is described as irregular.
- Aestivation is the arrangement of accessory floral organs (sepals / Petals) is relation to one another in the floral bud.
⇒ Open ⇒ valvate (Eg : Brassica)
⇒ Twisted (Eg: China rose)
⇒ Imbricate (Eg : Cassia)
⇒ Pappilanaceous (Eg : Pea)
- When there is no distinction of sepals and petals, the non essential floral organs are collectively called perianth. (Tepals) Eg : Asphodelus, onion, lily.
- A stamen of a flower is made up of 2 parts (i) filament and (ii) anther. Each anther has 2 lobes which are attached at the back by a sterile band called the connective.
- Sterile and undeveloped stamens are called staminodes.
- When both the anther lobes are present, stamen is called dithecous and when a single anther lobe is found, it is termed as monothecous (Eg : shoe flower)
- The free stamens are called polyandrous which may be equal or unequal in length
⇒ unequal [Tetradynamous Eg . Mustard]
⇒ equal [eq . Ocimum]
- The stamens are fused by their filaments only
⇒ Single group (Monadelphous eg : china rose)
⇒ 2 groups (Diadelphous eg : pea)
- The anthers may be attached to the filaments by any of the following 4 methods.
⇒ Basifixed / Innate [Mustard, Radish]
⇒ Adnate [Ranunculus, magnolia]
⇒ Dorsifixed [passiflora, sesbania]
⇒ Versatile [Grass]
- Carpels or female parts of a flower develop from the central region of thalamus the free occurring unit of gynoecium is called pistil. [Ovary, style and stigma]
⇒ unilocular - (Pea)
⇒ Bilocular - (Mustard)
⇒ Trilocular - (Asparagus)
- In the chambers are present oval outgrowths called ovules attached to a flattened cushion like placenta
- The number, position and arrangement or distribution of placenta inside a ovary is called placentation.
⇒ Marginal - Eg: Pea, Acacia, Cassia
⇒ Parietal - Eg. Fumaria, viola
⇒ Axile - Eg. Althaea, Petunia, Asphodelus
⇒ Free central - Eg silene, primula, sink
⇒ Basal - Eg. Sunflower, marigold, ranunculus
- There are three forms of thalamus as regards the insertion of pistil (or) other floral organs (Ovary - superior)
⇒ Hypogyny [Thalamus is convex/conical ; floral organs are inferior] Eg : Ranunculus, Mustard, Petunia etc.
- Perigyny : Thalamus is disc shaped / flask shaped ; Androperianth is borne around / above the level of ovary eg : Pea, cassia, Prunus
- Epigyny : Flask shaped - Thalamus ; Androperianth is brone above the level of ovary gynoecium - inferior [Eg : Apple, Sunflower, Guava]
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