Hybridization in the Annual Sunflowers: Helianthus annuus x H. argophyllus

Helianthus annuus and H. argophyllus are closely related species and natural hybrids between the two have been found in Texas. The artificial hybrid has been analyzed, and although showing some sterility, is more fertile than previously studied hybrids between other annual sunflowers. The artificial backcross plants approach very closely the recurrent parent in appearance, although they show some reduction in fertility. Analysis of meiosis in the F hybrid revealed 13 to 15 bivalents and one or two chains of four chromosomes in the majority of the ceils. Whether introgression has occurred between these two species is not yet clear. Barriers imposed by the habitat, sterility and time of blooming have been effective in preventing the amalgamation of these two species under natural conditions.