Flower Flashcards
STRUCTURE OF A FLOWER
● Flower is the specialized shoot in which the leaves are modified into floral structures.
● Flower has a stalk or a pedicel that supports the flower.
● Flowers can be stalked and as well as sessile i.e. without stalk.
● The stalk of the flower extends to form a cup shaped receptacle/thalamus
FLORAL PARTS ON THALAMUS
● First whorl: small green sepals collectively called sepals.
● Second whorl: large brightly colored petals collectively
called corolla.
● Third whorl: long filament ending into bilobed anther
together called stamen. Stamens are collectively called
androecium.
● Fourth whorl: formed of single or fused carpel units
called gynoecium/pistil. Each carpel consist of a basal ovary, middle style and uppermost stigma.
COMPLETE AND INCOMPLETE
FLOWER
● The flower with all four floral whorls is called a complete/perfect flower.
● The flower in which one or more floral whorls are missing is called an incomplete flower.
ESSENTIAL AND NON ESSENTIAL PARTS
● The parts of the flower that are directly involved in the process of reproduction are called essential whorls, like the stamens and the carpels.
● The parts of the flower that are simply the helping (attractive) and protecting units are called essential whorls, like the petals and sepals. Also, bracts and nectaries are non essential parts.
PERIANTH
● At times, petals and sepals remain undifferentiated forming perianth. Units here are called tepals
● If the perianth appears to be green like sepals it is called sepaloid perianth and if it is colourful and attractive like petals it is called petaloid.
OTHER NON ESSENTIAL PARTS
BRACTS: The leaf like (or sometimes colored) structure in whose axil the flower arises is called bract. When colourful it is usually mistaken to be a petal.
NECTARIES: they are usually located at the base of the pistil or on the bases of petals.
Consists of nectar secreting cells. Eg. Nasturtium.
SEXUALITY IN FLOWERS
There are three types of flowers based on sexuality i.e. Bisexual, Unisexual and Neuter flowers.
The anthers of the stamens produces pollen grains (male gametes) and the ovary of the carpel bears the ovule which encloses egg cell (female gamete). ● Bisexual /Hermaphrodite: A flower which has both stamens and carpels.
● Unisexual/Imperfect: A flower containing only the stamens is called male/staminate flower and that containing only the carpels is called female/pistillate flower.
● Neuter: A flower in which both male and female reproductive parts are absent is called a neuter flower.
CALYX
● Also called sepals, usually five or more in number.
● Sepals if free, polysepalous condition and if fused gamosepalous
condition.
● In some cases, a second series of sepals called episepals is present,
collectively called epicalyx.
● Sepals are usually green but can be colorful as in gulmohur so called
petaloid sepal.
● Sepals protect the young flower bud and when green aids in
photosynthesis.
COROLLA
● Also called petals, usually in a single whorl(five in nos) but can be sometimes double whorled (like in poppy) or arranged in spiral(water lily).
● Petals if free, polypetalous condition and if fused gamopetalous condition.
● Petals when fused can form tube or funnel shape.
● Petals attract insects for pollination and also protects stamens and
pistils especially when in tube form.
ANDROECIUM
● Units called stamens may vary in number in different flowers.
● Each stamen has a filament that ends into two lobed anther
lobes containing pollen sacs that contain pollen grains.
● At maturity, pollen sacs rapture to liberate pollen grains.
● Pollen grains are powdery particles of different shapes and
size.
● Here, stamens may be free or united in different ways to form
single, double or several groups.
COHESION OF STAMENS
● Monadelphous: Stamens are united in one group by their filament, only anthers are free. Eg. China rose, cotton.
● Diadelphous: The filaments are united in two bundles. Eg. Pea (out of ten, nine stamens form a staminal tube while one is free).
● Polyadelphous: The filaments here are united in several groups. Eg. Bombax.
GYNOECIUM
● Also known as pistil and is composed of one or two carpels. Each carpel has a stigma, style and ovary.
● Stigma is the terminal knob like structure. It can be one to more lobed or feathery in appearance.
● Its hairy or glandular to trap the pollens within it.
● Serves as the landing place for pollens during
pollination.
● Style is the slender stalk which connects the stigma to the ovary, serves as path for pollens to travel to ovary.
● Ovary is the basal swollen portion having one or many carpels. Inner cavity of ovary may be single or divided into multiple locules containing ovules in them. Placentation is the manner in which the ovules are arranged to the wall of ovary.(Placenta is the tissue that attaches the ovule to the wall of the ovary).
● Ovules turn into seeds in the mature fruit(ovary).
SEXUALITY IN PLANTS
● Based on the types of flowers borne by the plant it is of three types:
(i) Bisexual plants: Bears bisexual flowers. Usually all plants are bisexual.
(ii) Monoecious plants: Bears both male and female flowers on same plant. Eg. cucumber, pumpkin.
(iii) Dioecious plants: Bears male and female flower both on different plants. Eg. palm, papaya.
INFLORESCENCE
● Inflorescence is the mode of arrangement of flowers on the axis of the plant.
● It can be single either at the apex of the main stem or lateral branches.
● Also, it can occur in the axils of the leaves.
● It can grow out from the axils of different leaves reaching at
the same level to form cluster.
● Pedicel of the flower flattens into disc as in sunflower, bearing
younger flowers at centre and oldest towards the periphery.
