Define perigynous flower.

Hint: In the flowering plants, an ovary is a part of the female reproductive organ of the flower i.e. the gynoecium. Based on the position of the ovary, flowers are categorized into three types. These are Hypogynous, Epigynous, and Perigynous flowers.

Complete answer:
In perigynous flowers, a hypanthium which is also known as the floral tube formed from the fusion of the stamens, petals, and sepals is attached below the carpel and surrounds the ovary. The ovary in this case is inferior, and the free parts of the petals, sepals, and stamens are attached to the rim of the thalamus or hypanthium. Example- Rose, peach, etc.

Additional Information: The terminology of the positions of ovaries is determined by the insertion point, where the other floral parts such as sepal, petal, and androecium come together and attach to the surface of the ovary. The flowers can thus be classified as Hypogynous, Epigynous, and Perigynous flowers.
Hypogynous flower: Here the gynoecium is located at the highest point i.e. the ovary is superior and other parts like sepals, petals, and androecium are situated below it. Example- china rose, brinjal, etc.
Epigynous flower: Here, the gynoecium is located inferior to the other floral parts. The sepals, petals, and androecium attach to the upper part of the ovary. Example- apple, cucumber, daffodil, etc.

Note: The presence of a hypanthium is known to be an important and the basic feature of some families of plants, particularly the Rosaceae and Grossulariaceae families. It stores the nectar of the flower. In roses, it is named as 'hip' whereas, in eucalyptus, it is known as 'gum nut'.