A cyathium (plural: cyathia) is one of the specialised pseudanthia ("false flowers") forming the

inflorescence An inflorescence is a group or cluster of flowers arranged on a Plant stem, stem that is composed of a main branch or a complicated arrangement of branches. Morphology (biology), Morphologically, it is the modified part of the shoot of sperma ...

of plants in the genus ''

Euphorbia ''Euphorbia'' is a very large and diverse genus of flowering plants, commonly called spurge, in the family Euphorbiaceae. "Euphorbia" is sometimes used in ordinary English to collectively refer to all members of Euphorbiaceae (in deference to t ...

'' (

Euphorbiaceae Euphorbiaceae, the spurge family, is a large family of flowering plants. In English, they are also commonly called euphorbias, which is also the name of a genus in the family. Most spurges, such as '' Euphorbia paralias'', are herbs, but some, ...

). 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). These alternate with: * 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 of ''Euphorbia'' section ''Goniostema'' are called ''cyathophylls''. here female to male flower ratio is 1:α The cyathia are sometimes solitary, but are usually in cymes,

inflorescences An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed ...

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 subfamily 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

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s, the cyathia have become specialised: Most cyathia have upright cyathophylls 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.

References

* Sandro Pignatti, Flora d'Italia, Edagricole, Bologna 1982. {{ISBN, 88-506-2449-2 Plant morphology Euphorbia