NEET Biology Notes Morphology of Flowering Plants Aestivation
- The mode of arrangement of sepals or petals in a flower bud is known as aestivation. It may be
Valvate The sepals or petals are placed, so that their edges touch each other but not overlap,
e.g. Solarium and Calotropis.
- Twisted (contorted) One margin of petal overlap that of next one and other margin is covered over by margin of adjacent petal,
e.g. China rose, cotton and lady finger.
- Imbricate Both margins of one of the petals covered by others and both margins of another one are external and of the remaining three petals one margin is overlapped, while other overlapping,
e.g. Cassia and Caesalpinia.
- Quincuncial An imbricate type aestivation with 5 petals or sepals, out of which 2 are exterior, 2 interior and the 5th one has one exterior and one interior margin, e.g. Ipomoea and Ranunculus.
- Vexillary Descending imbricate (papilionaceous-) in which out of 5 petals the posterior one is largest (standerd or vexillum) and cover the two lateral petals (wings), the lateral overlap the 2 smallest anterior petals (keel), e.g. family-Papilionatae.
Some Important Floral Terms
The important floral terms for the description of a flower are given below:
- Actinomorphic Flower
When the flower is radially symmetrical (divisible into two or more equal halves by any radial plane), it is termed as actinomorphic,
e.g. mustard (Cruciferae), onion (Liliaceae), brinjal (Solanaceae),
- Zygomorphic Flower
When the flower is bilaterally symmetrical, (divisible into only two equal halves by a single vertical plane) it is termed as zygomorphic,
e.g. adhatoda, pea, larkspur and Ocimum.
- Asymmetric Flower
Flower, which cannot be divided into two equal halves by any vertical plane passing through the centre, is called asymmetric flowers,
- Unisexual vs Bisexual
Bisexual, hermaphrodite or monoecious flower contains both male and female reproductive organs, e.g. China rose, mustard, Papaver, pea, cotton, Datura, etc.
Unisexual or dioecious flower has only one essential floral whorl, either androecium (staminate or pistalloide) or gynoecium (pistillate or staminode),
e.g. Moms alba, papaya and Cucurbita.
- Complete and Incomplete Flower
A flower is called complete, when it contains all floral whorls, i.e. calyx, corolla, androecium and gynoecium, e.g. Solanum, mustard; while flower with absence of any one of these four whorls is called incomplete flower,
- Regular and Irregular Flower
When the flower of a plant have same size, shape, colour and arrangement of various floral whorls/ organs, then the flower is called regular and if any flower of a plant shows dissimilarity in any of it’s part or trait, then the flower is called irregular.
- Cyclic and Acyclic Flower
When the floral parts of a flower are arranged in a whorl, the flower is called cyclic, e.g. Solanum and if the floral parts of a flower are arranged spirally and not in whorls, the flower is called acyclic, e.g. Ranunculus, Opuntia and Nymphaea.
Achlamydous, Monochlamydous and Dichlamydous Flowers
In achlamydous flowers, the accessory floral whorls (calyx and corolla) are absent, e.g. Piper sp. (Piperaceae) and when a flower contains only one accessory whorl (either calyx or corolla) or perianth (a collective term given to a group of undifferentiate calyx and corolla), it is called monochlamydous, e.g. Polygonum (Polygonaceae), onion (Liliaceae), the condition dichlamydous is observed when both the accessory whorls (calyx and corolla) are present, e.g. in most of the flowers.
- Isomerous and Heteromerous Flowers
When the parts of a floral whorl are found in a particular basic number or its multiple the situation is called isomary and the flower is called isomerous. An isomerous flower may be dimerous (2 or multiple of 2), e.g. poppy or trimerous (3 or multiple of it), e.g. Argemone or tetramerous (4 or multiple of 4), e.g. Solanum. A flower is called heteromerous when different parts of different floral whorls have different basic number of its multiple.
- Hypogynous, Perigynous and Epigynous Flowers
A flower is called hypogynous when the innermost floral whorl (gynoecium) occupies the highest position (superior) viz., androecium. Corolla and calyx successively arise below it (inferior), e.g. Brassica, China rose, Papaver, Citrus, Solanum, cotton, etc. In perigynous flower all the floral whorls are occurred at the same level of height on the thalamus so they are called half superior or half inferior, e.g. rose, peach, Prunus and Plum.
In an epigynous flower, the innermost whorl, i. e. gynoecium is covered by the elongated margins of thalamus thus, their position is inferior in regard to other floral whorls, which arise above the ovary and thus called superior, e.g. the ray florets of sunflower, Cucurbita, guava and coriander.
- Bracteate and Ebracteate Flowers
Bract is a small leaf like structure whose axil bears a pedicel (flower stalk). A flower containing bract is called bracteate, e.g. Adhatoda and those without bract are called ebracteate,