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 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 o ...

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, e ...

). A cyathium consists of: * Five (rarely four) bracteoles. These are small, united

bract In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves. They may be smaller, larger, or of ...

s, 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 gland Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualis ...

s, which are sometimes fused. * One extremely reduced female flower standing in the centre at the base of the involucre, consisting of an

ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...

on a short stem with

pistil Gynoecium (; ) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more) ''pistils'' ...

, 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 The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filam ...

on a stem. The flower-like characteristics of the cyathia are underlined by brightly coloured nectar glands and often by

petal Petals are modified Leaf, leaves that surround the reproductive parts of flowers. They are often advertising coloration, brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''c ...

-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 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 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 lightweigh ...

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