New hybrids were developed at the U.S. Water Conservation Laboratory, Phoenix, Arizona, between these short-day flowering types and an accession flowering under any day length. They have been grown successfully in Arizona, Kentucky, Missouri, Oregon, Texas, Virginia, and northern Argentina. Commercial development of these hybrids depends on further improvement of seed yields. Unknown but pollen is allergenic. Other annual species of Vernonia appear to be unrelated.
Workers acknowledge that there is a striking range of variation even within botanical varieties.
The capitula is made up of 50 to 150 florets. This roughly corresponds to the number of seed produced per capitula, depending on pollination events. Subspecies readily hybridize among themselves. All of the taxa, except for a few accessions of V. galamensis spp. Most plants will flower after receiving 5 to 10 short days of 11h light and 13 h dark periods.