Question

Define the following terms:
a) Aestivation
b) Placentation
c) Actinomorphic
d) Zygomorphic
e) Superior ovary
f) Perigynous flower
g) Epipetalous stamen

Answer 1

Hint: In flowering plants, flower is the reproductive part which ensures the continuance of a species by the process of reproduction. A typical flower grows on a stalk and has a swollen tip called thalamus. The thalamus bears two essential and two non-essential whorls. a calyx, corolla, androecium and gynoecium.

Complete answer:
a) Aestivation:
The manner in which sepals, petals and tepals are arranged on the thalamus with respect to each other is called aestivation. Five types of aestivation in plants have been observed. These are:
- Valvate aestivation e.g. Calotropis
- Twisted aestivation e.g. Hibiscus
- Imbricate aestivation e.g. Gulmohar
- Vexillary aestivation e.g. Beans
- Quincuncial aestivation e.g. Guava

b) Placentation:
The arrangement of ovules within the ovary is known as placentation. In flowering plants, five types of placentation are found. These are:
- Marginal placentation e.g. Pea
- Axile placentation e.g. Lemon
- Parietal placentation e.g. Mustard
- Basal placentation e.g. Marigold
- Free central placentation e.g. Primrose

c) Actinomorphic:
Flowers that show radial symmetry are called actinomorphic flowers. Such flowers when divided in a plane passing through the centre will always have identical parts. E.g. Lily, mustard, etc.

d) Zygomorphic:
Flowers that can be divided into two identical halves only through one plane of symmetry are called zygomorphic flowers. E.g. Peas, Snapdragon, etc.

e) Superior ovary:
In a flower, when an ovary is attached above other floral parts then the condition is called a superior ovary. E.g. Brinjal, mustard, etc.

f) Perigynous flower:
in a flower, when the ovary is in the centre and all four whorls like calyx, corolla, androecium and gynoecium are arranged at the same level on the thalamus, such flowers are called perigynous. E.g., rose, peach, cherry, etc.

g) Epipetalous Stamen:
The condition when stamens are attached to the petals then they are called Epipetalous stamens. E.g. brinjal.

Note: Androecium and gynoecium form the actual reproductive parts of a flowering plant. Androecium is the male reproductive part of the flower and consists of stamens. Gynoecium consists of a pistil and is the female reproductive part of the flower. It is made up of one or more free or united carpels. Each carpel contains a stigma, a long style and an ovary at bottom. The position of Ovary is a useful feature in classification.