Arrangement of Floral Parts
Position of Ovary
When the ovary occupies the highest position and other floral parts are below it, the flower is called hypogynous. In this case, the ovary is said to be superior, e.g. mustard, China rose, brinjal, etc.
When the ovary and other parts of the flower are situated at the same level, the flower is called perigynous. In this case, the ovary is said to be half-inferior, e.g. plum, rose, peach, etc.
When the ovary occupies the lowest position and other floral parts are situated above it, the flower is called epigynous flower. In this case, the thalamus grows upwards and completely covers the ovary. In this case, the ovary is said to be inferior, e.g. guava, cucumber, etc.
The mode of arrangement of sepals or petals, with respect to the other members of the same whorl is called aestivation. Following are the main types of aestivation:
When sepals or petals just touch one another at the margin and don't overlap, this arrangement is called valvate, e.g. Calotropis.
When the margin of one sepal or petal overlaps the margin of the next and so on, this arrangement is called twisted, e.g. China rose, okra, cotton, etc.
When the margins of sepal or petal overlap one another but the overlapping does not follow a set pattern, this arrangement is called imbricate, e.g. Cassia and gulmohar.
When the largest petal overlaps the two lateral petals, which in turn overlap the two smallest anterior petals, this arrangement is called vexillary. The largest petal is called the standard, the lateral petals are called wings and the smallest petals are called keel. Examples: pea and bean.
Type of Attachment of Androecium
- Epipetalous: When stamens are attached to the petals, this arrangement is called epipetalous, e.g. brinjal.
- Epiphyllous: When stamens are attached to the perianth, this arrangement is called epiphyllous, e.g. lily.
Arrangement of Stamens
- Monoadelphous: When stamens are united into one bunch, they are called monoadelphous, e.g. China rose.
- Diadelphous: When stamens are arranged in two bundles, they are called diadelphous, e.g. pea.
- Polyadelhpous: When stamens are in more than two bundles, they are called polyadelphous, e.g. citrus.
Arrangement of Gynoecium:
- Aporcarpous: When carpels are free, they are called apocarpous, e.g. lotus and rose.
- Syncarpous: When carpels are fused, they are called syncarpous, e.g. mustard and tomato.
The arrangement of ovules in the ovary is called placentation. There are different types of placentation which are as follows:
When the placenta forms a ridge along the ventral suture of the ovary and ovules are borne on this ridge, in two rows, this arrangement is called marginal, e.g. pea.
When the placenta is axial and the ovules are attached to it in a multiclocular ovary, this arrangement is called axile, e.g. China rose, tomato and lemon.
When ovules develop on the inner wall of the ovary or on peripheral part, this arrangement is called parietal, e.g. mustard and argemone.
When ovules develop on the central axis and septa are absent, this arrangement is called free-central, e.g. dianthus and primrose.
When the placenta develops at the base of the ovary and a single ovule is attached to it, this arrangement is called basal, e.g. sunflower, marigold.