Head (botany)

From Wikipedia, the free encyclopedia

Diagram of a flower head. Note bracts surrounding the flowers, which would be absent on a capitulum.

Flower head of a common daisy (Bellis perennis)

Flowers open in succession in head of a sunflower (Helianthus annuus)

In botany, a head or flower head is an inflorescence composed of numerous individual flowers (=florets) that share the same basis and grow so closely together that they would appear to be a single flower. A head where the bracts form an involucre under the basis is called a capitulum (pl. "capitula").^[1] "Capitulum" and "head" are often used interchangeably.^[2]

Capitula are most commonly found in Asteraceae, where they may be composed of one or two different types of florets: disc florets are tightly packed at the center, and have tubular corollas, and are surrounded by ray flowers. The "petals" are the single petal of the ray flowers, often called ligule. Asteraceae capitula are composed only of ray flowers (dandelions, Taraxacum), only disc flowers (pineapple weeds, Matricaria discoidea), or a combination thereof (sunflowers, Helianthus). The capitulum is considered the most evolved form of inflorescence^[3] Flower heads found outside Asteraceae (such as those of Eryngium or Jasione) shows lesser degrees of specialization.

[edit] References

^ Allaby, Michael (1992). The Concise Oxford dictionary of botany. New York: Oxford University Press. ISBN 0-19-866163-0.
^ Usher, George (1966). A dictionary of botany, including terms used in bio-chemistry, soil science, and statistics. Princeton: Van Nostrand. LCCN 66-25447.
^ Hutchinson, John (1964). The genera of flowering plants (Angiospermae). Oxford: Clarendon Press. LCCN 65-676.