Ray Florets Notes

Ray Florets are the small, strap-shaped, marginal flowers present in the head or capitulum inflorescence of plants of the Asteraceae or Compositae family, such as Helianthus annuus (sunflower).

Capitulum

The capitulum is a type of racemose inflorescence with a flattened main axis. It is the characteristic of the Asteraceae family and contains small, sessile flowers arranged in a centripetal manner on a receptacle. In this arrangement, the older flowers are present at the periphery and the younger flowers are present at the centre.

The flowers of Helianthus annuus (Sunflower) and Tagetes erecta (Marigold) have bracteate inflorescences surrounded by two to three whorls of bracts (involucre). The group of flowers on the receptacle gives the appearance of a single flower.

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 either actinomorphic (radially symmetrical) or zygomorphic (bilaterally symmetrical with five fused petals).

On the basis of the presence of different types of flowers, the capitulum head can be classified into 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 on the margins.
  • 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, which are usually bisexual, meaning they have both male and female reproductive parts.

Disciform head - This type of head contains only disc florets, with no ray florets present. Pistillate flowers are located at the outer margin.

Ligulate head - The ligulate head consists of only ligulate flowers. These flowers are similar to ray flowers, but they are bisexual and perfect, as opposed to ray florets which are usually sterile female flowers.

Ray Florets

Ray florets are typically strap-shaped and 2-3 lobed. They are usually zygomorphic, with a fused and tubular corolla base. The tongue-shaped part of the corolla is known as a ligule or ray, and the ray florets are usually sterile. The sterile female flowers have a vestigial ovary.

Disc Florets

Disc florets are located in the center of the head and are typically actinomorphic. The flowers have a tubular corolla and the petals are fused together, with a top that has 4-5 apical teeth. Disc florets can be unisexual or bisexual and are usually complete and fertile.

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