1. A non-acropetal sequence has long been recognized for species with secondarily or tertiarily condensed heads, but species with uncondensed heterogamous heads also display some degree of departure from the strictly acropetal plan.

2. The inflorescence of sunflower (Helianthus annuus L.) is heterogamous with zygomorphic ray flowers located in the outermost whorl of the head and actinomorphic disk flowers arrayed in arcs radiating from the center of the head.

3. Furthermore, the production of morphologically and ecologically indistinguishable ray and disc achenes by A. umbellatus var. umbellatus would suggest that the significance of heterogamous capitula, specifically the production of ray florets, rests in their attractiveness of pollinators.