Ovary position is an extremely important taxonomic character
- Primitive: Superior ovary and flower hypogynous, with the stamens, petals, and sepals attached below (hypo-) the gynoecium.
- Derived: Superior ovary and flower perigynous, The flower has a hypanthium that is free from the ovary, with the stamens, petals, and sepals ttached to the edge of the hypanthium.
- Most derived: Inferior ovary and flower epigynous, with the stamens, petals, and sepals attached above the gynoecium.
Development of epigyny via perigyny
Perigyny: hypanthium surrounds ovary (free hypanthium)
Hypogyny: hypanthium fuses to ovary wall to give a truly inferior ovary. Adnation of the hypanthium (bases of sepals, petals, and stamens fused) to the ovary wall.
This is the mechanism in most families that have an inferior ovary – we can often still see the separate vascular bundles to each type of floral parts (stamens, sepals, petals)
Development of epigyny via expansion of the receptacle
- Adnation and expansion of the receptacle around the ovary (Cactaceae, Aizoaceae, and Santalaceae)
- Receptacle (stem tissue) surrounds the ovary. Often vascular bundles of the stem loop up into the ovary wall indicating the presence of receptacle tissue
- In some Cactaceae it is obvious that the inferior ovary is surrounded by stem tissue because nodes (called areoles in cacti) are visible on the ovary.
Inferior ovary of Fuchsia – hypanthial
Inferior ovary in Opuntia (Cactaceae) - stem tissue is evident around ovary, as it bears little spines (modified leaves)