Cyathium
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The very special Pseudanthia in the genus Euphorbia (Euphorbiaceae) are known as Cyathia. A cyathium consists of:
- five (rarely four) bracteoles. These are small, united bracts, which form a cup-like involucre. Their upper tips are free and in the beginning cover the opening of the involucre (like the shutter of a camera). With these alternate:
- five (1 to 10) nectar glands, which are sometimes fused.
- one extremely reduced female flower standing in the centre at the base of the involucre, consisting of an ovary on a short stem with pistil, and surrounded by:
- five groups (one group at the base of each bracteole) of extremely reduced male flowers, which each consist of a single anther on a stem.
The flower-like characteristics of the cyathia are underlined by brightly coloured nectar glands and often by petal-like appendages to the nectar glands, or brightly coloured, petal-like bracts positioned under the cyathia. The paired petal-like bracts in the sub-family Euphorbia section Goniostema are called cyathophylles.
The cyathia are rarely solitary, but mostly in cymes, inflorescences of the second order: in pseudumbels, on dichotomously branched stalks or in so called simple cymes which consist of one central and two lateral cyathia.
In one group of Madagascan species in the sub-family Euphorbia section Goniostema (E. aueoviridiflora, E. capmanambatoensis, E. iharanae, E. leuconeura, E. neohumbertii, E. viguieri) there is a tendency for a further pseudanthium to grow from the cyme. Probably as an adaptation to pollination by birds, the cyathia have become specialised: Most cyathia have upright cyathophylles which surround them protectively, but render the nectar glands inaccessible. To compensate, between them are naked sterile cyathia whose only job is to produce nectar.
