Ray Florets are the small, strap-shaped, marginal flowers present in the head or capitulum inflorescence. It is the characteristic of plants of the Asteraceae or Compositae family. E.g. Helianthus annuus (sunflower).
Capitulum
The capitulum is a type of racemose inflorescence with a flattened main axis. The capitulum or head is the characteristic of the Asteraceae family. The capitulum contains small, sessile flowers arranged in a centripetal manner on a receptacle. In the centripetal arrangement, the older flowers are present at the periphery and the younger flowers are present at the centre.
The flowers are bracteate and the inflorescence is surrounded by two to three whorls of bracts (involucre). The group of flowers on the receptacle look like a single flower. E.g. Helianthus annuus (Sunflower), Tagetes erecta (Marigold), etc.
Flowers or florets are sessile. They are sterile, unisexual or bisexual. It contains two types of flowers, the centrally placed disc florets, which is surrounded by ray florets. Ray florets and disc florets have inferior ovaries.
The florets are actinomorphic, i.e. radially symmetrical or zygomorphic, i.e. bilaterally symmetrical with five fused petals.
On the basis of the presence of different types of flowers, the capitulum head is of various types:
- Radiate head – It contains both disc florets and ray florets. The disc florets are centrally placed and are surrounded by one or two rows of ray florets arranged marginally. The ray florets are female or sterile female flowers. The disc florets are mostly bisexual or staminate.
- Discoid head – This type of head contains only disc florets. Florets are mostly perfect having both male and female reproductive parts, i.e. bisexual.
- Disciform head – This type of head also contains only disc florets and the ray florets are absent. It contains pistillate flowers at the outer margin.
- Ligulate head – The ligulate head has only ligulate flowers. They are similar to ray flowers but are bisexual and perfect in contrast to ray florets, which are normally sterile female flowers.
Ray Florets
Ray florets are strap-shaped. It is 2-3 lobed. They are mostly zygomorphic. Corolla are fused and tubular at the base. The tongue of the corolla is strap-shaped and is known as a ligule or ray. Ray florets are normally sterile. The sterile female flower has a vestigial ovary.
Disc Florets
Disc florets are present in the centre of the head. They are usually actinomorphic. Flowers have tubular corolla. Petals are fused. The top of the petals has apical 4-5 teeth. Disc florets can be unisexual or bisexual. They are normally complete and fertile.
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