Britannica Sources used in this answer

How does a radiate flower head differ from a discoid flower head?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Sunflower — Asteraceae The flowering head of a sunflower (*Helianthus annuus*) is formed of yellow, petal-like ray flowers and a brown center of minute disk flowers.

In the Asteraceae family, the primary difference between these flower heads lies in the types of florets they contain:

Discoid heads: These consist entirely of disk flowers, which possess regular, tubular corollas with four or five apical teeth. These flowers are typically perfect (bisexual) and fertile. Examples include thistles and ageratums.1
Radiate heads: These feature a central cluster of disk flowers surrounded by one or more marginal rows of ray flowers. Ray flowers have an irregular corolla that is tubular at the base but extends into a flat, petal-like projection called a ray or ligule. These ray flowers are typically pistillate (female) or neutral.12

While discoid heads are uniform in their tubular structure, radiate heads are distinguished by the presence of these showy, strap-shaped marginal florets.1