Helianthus verticillatus Small (Asteraceae), also known as the whorled sunflower, is a federally listed, endangered sunflower found exclusively in the southeastern United States. Helianthus verticillatus was originally collected as a different species (H. schwinitzii) in 1892 by Samuel McCutcheon Bain, then was described as a new species by John K. Small in 1898. After its discovery, the species was not seen again for over 100 years until 1994 when it was rediscovered in Floyd County, Georgia by Richard T. Ware and identified by James R. Allison. Allison continued to search for populations and discovered another population in Cherokee County, Alabama. In 1998, Carl Nordman of the U.S. Fish and Wildlife Service discovered a third population of H. verticillatus 10 km northwest from where Bain originally collected the type specimen in Madison County, Tennessee. In 2006, a fourth population was discovered in McNairy County, Tennessee by Andrea Bishop.
Helianthus verticillatus was listed as federally endangered by the United States Fish and Wildlife Service in 2014. Researchers and conservation managers believe that the biggest threats to the known populations are modifications of remnant prairie habitats and the loss and degradation of habitat which is causing extensive geographic distance between known populations, making cross-breeding between populations very limited. Also, important to note that H. verticillatus is self-incompatible and reproduces sexually and asexually in the form of ramets. Thus, the extremely restricted distribution, small population sizes, and reproductive limits make the species extremely vulnerable to localized extinction.
There is hope!
In 2017, a new population of H. verticillatus was discovered in Marshall County, Mississippi by botanist Darrell Brandon. Then in 2019, another population was discovered in Franklin County, Virginia by plant ecologist Christopher Ulrey of the National Park Service (pictured to the left).
Given these newly discovered sites, I designed a study that compared the Mississippi and Virginia populations to the four previously known populations to better understand their total genetic variation. What I have found is that the Mississippi population is genetically very different to the other new populations and is shown to be geographically isolated (unpublished data). Given what we know about H. verticillatus, these results were unusual since the population does not seem to be breeding with the other known populations, but is still seen as genetically highly diverse. So, I thought: well, there must be other unknown populations that it is breeding with.
Mississippi land survey (2020)
On September 14th, 2020, I got to go on my first land survey in Mississippi in search for additional populations of H. verticillatus. I was joined by Jennifer Mandel (University of Memphis), Cooper Breeden (Southeastern Grasslands Initiative), Stephanie Green (Strawberry Plains Audubon Center), and Heather Sullivan (Mississippi Museum of Natural Science). Helianthus verticillatus is usually found in wet, prairie habitats, so we started searching a couple miles away from the original collection site along a riverbank. We found multiple Helianthus species along the way: H. tuberosus , H. microcephalus, H. angustifolus, and (potentially) H. grosseserratus. But of course, that wasn't what we went there for.
After an afternoon of searching, we were able to find potentially three additional populations of H. verticillatus! There were some specimens that were morphologically variable, meaning they will need to be keyed more intently to determine species status. One population that was found meets all the criteria of being H. verticillatus (prominent midvein, enough phyllaries, whorled leaves, etc.), so we feel pretty confident saying that we have found at least one new cluster. Given the natural morphological variability of Helianthus species, it is hard to know for sure. So, we hope that these new populations lead to additional and larger studies to better understand H. verticillatus population structure, as well as provide information that will grant protections on these newly discovered populations to ensure that H. verticillatus remains genetically diverse. The Mississippi population is currently mowed or sprayed annually, making it highly vulnerable.
If you have any questions or comments, please feel free to contact me!