Describe the arrangement of floral members in relation to their insertion on thalamus.

Based on the position of the calyx, corolla, and androecium with respect to the ovary on the thalamus, the flowers can be grouped into three categories that are hypogynous, perigynous, and epigynous.
Hypogynous flowers – In this the ovary occupies the highest position on the thalamus while other floral parts are situated below it. In such flowers, the ovary is superior. e.g., China rose, mustard etc.

Perigynous flowers: The ovary is situated at the centre and other floral parts are arranged on the rim of the thalamus. The ovary here is said to be half inferior.  e.g., plum, rose, peach. 

Epigynous  flowers: The thalamus grows around the ovary fusing with its wall. The other floral parts are present above the ovary. Hence, the ovary is said to be inferior e.g., flowers of guava and cucumber.