A hypanthium is a cup-like or tubular part of a flower whose rim bears the stamens and perianth, including sepals and petals when both are present. It forms around the region occupied by the ovary. The shape of the cup and its relationship to the ovary are separate features: a hypanthium need not be fused to the ovary along its sides.[ref]
Glossary of Botanical Terms by PlantNET. Entry hypanthium and Figure 12D, a cup-shaped hypanthium around a superior ovary; plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?glossary=yes&ill=Fig.+12+D&page=nswfl&term=hypanthium
The apple provides a familiar consequence of this arrangement. During development of this pome, tissues around the ovary enlarge into much of the edible flesh, while the ovary contributes the central core. A longitudinal slice therefore reveals more than the wall of a swollen ovary: it contains tissues derived from different parts of the original flower. This distinction matters when asking which tissues undergo cell division and which increase in cell size during fruit growth.[ref]
Global gene expression analysis of apple fruit development from the floral bud to ripe fruit by Bart J. Janssen and others. Background, expanding ovary/core and hypanthium/cortex; Results, developmental sampling stages
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