Biol 324 Introduction To Seed Plant Taxonomy

Hypanthium - A logical consequence of the adnation of floral parts (fusion of adjacent whorls)

- Evidence of fusion of floral parts may be gained from vascular patterns.
- Fused organs may have separate vascular systems (particularly if fusion is evolutionarily recent)
- However fusion may become “complete”, with a common vascular supply.

Examples of adnation (fusion of unlike parts)
- EPIPETALOUS stamens, the fusion of stamens to petals (typically a corolla tube). Epipetaly is especially common in flowers with tubular corollas

The hypanthium is a tubular, cup shaped, bowl shaped, or saucer shaped part of the flower, to which the stamens, petals, and sepals are attached at the rim.
- In Fuchsia it represents the fusion of the bases of the sepals, petals, and filaments of the stamens.
- In the Cactaceae and some other families, and in the genus Rosa, the hypanthium is wholly or partly receptacle, and therefore anatomically different.

As the rose hip is a hypanthium (in this case outgrowth of the receptacle) – it is a false fruit. Each free carpel inside the hypanthium is a true fruit.

Note on "fusion" as a developmental process
Fusion may be congenital, i.e. no separate organs ever form, fusion is complete throughout development, and homology with separate organs is inferred.
…. or - may be postgenital, i.e. separate organs form, come together during development and join, usually by dedifferentiation and interlocking of the epidermal cells.
The word "fusion" is not strictly accurate for congenital fusion, which is not a coming together but a failure in development to form separate organs.

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