Hypanthium

In a pomegranate flower, Punica granatum, the petals, except for their fused bases, soon fall. The hypanthium with sepal lobes and stamens still attached develops to form the outer layer of the fruit.

In angiosperms, a hypanthium or floral cup^[1]^[2]^[3] is a structure where basal portions of the calyx, the corolla, and the stamens form a cup-shaped tube. It is sometimes called a floral tube, a term that is also used for corolla tube and calyx tube.^{[citation needed]} It often contains the nectaries of the plant. It is present in many plant families, although varies in structural dimensions and appearance.^[4] This differentiation between the hypanthium in particular species is useful for identification. Some geometric forms are obconic shapes as in toyon, whereas some are saucer-shaped as in Mitella caulescens.

Its presence is diagnostic of many families, including the Rosaceae, Grossulariaceae, and Fabaceae. In some cases, it can be so deep, with such a narrow top, that the flower can appear to have an inferior ovary - the ovary is below the other attached floral parts. The hypanthium is known by different common names in differing species. In the eucalypts, it is referred to as the gum nut; in roses it is called the hip.

^ Foster 2014, Hypanthium.
^ Beentje, H.; Williamson, J. (2010). The Kew Plant Glossary: an Illustrated Dictionary of Plant Terms. Royal Botanic Gardens, Kew: Kew Publishing.
^ Hickey, M.; King, C. (2001). The Cambridge Illustrated Glossary of Botanical Terms. Cambridge University Press.
^ Cronquist 1981.

[FOOTNOTEFoster2014[httpplant-phytographyblogspotca201210hypanthium-cup-shaped-or-tubularhtml_Hypanthium]-1] Foster 2014, Hypanthium.

[2] Beentje, H.; Williamson, J. (2010). The Kew Plant Glossary: an Illustrated Dictionary of Plant Terms. Royal Botanic Gardens, Kew: Kew Publishing.

[3] Hickey, M.; King, C. (2001). The Cambridge Illustrated Glossary of Botanical Terms. Cambridge University Press.

[FOOTNOTECronquist1981-4] Cronquist 1981.

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