Clonal diversity, spatial dynamics, and small genetic population size in the rare sunflower, Helianthus verticillatus

Abstract

Knowledge of population size is an important step for identifying populations of immediate conservation concern. However, this task is difficult in plant species that exhibit clonal growth, since a simple ''head count'' may not be appropriate. Here, I determine the genetic population size and the extent of clonality in the four known populations of a rare sunflower, Helianthus verticillatus. Previous work in this species revealed high genetic diversity in all populations but significant fitness differences among them. In this study, populations exhibited high clonal diversity but consisted of far fewer genetic individuals than previously reported. Moreover, the clonal structure of populations was clumped, such that genotypes were highly clustered, which may promote selfing among genets. The results of this study are related to previously examined levels of genetic diversity and fitness, and findings are discussed in the context of the ecological and biological dynamics in clonal plant populations. Finally, the results of this study led to an upgrade in the priority status of this species for the Endangered Species List.

Floral Visitors to Helianthus verticillatus, a Rare Sunflower Species in the Southern United States

“…The whorled sunflower, Helianthus verticillatus Small, is a rare and federally endangered plant (U.S. Fish and Wildlife Service, 2014) found in only a few locations in the southern United States. This plant was described in 1892 by Samuel Bain (Ellis et al, 2006;Mandel, 2010;Matthews et al, 2002;Small, 1898) from collections obtained in Chester County, TN. The species was not collected again until 1993, when it was discovered in Floyd County, GA (Matthews et al, 2002).…”

“…Helianthus verticillatus are 2-to 4-m-tall plants that produce flowers from late August or early September to mid-October (Matthews et al, 2002) or until a killing frost. This sunflower is a self-incompatible and largely insectpollinated species (R. Trigiano, unpublished data) that does not lend itself to wind pollination (Mandel, 2010). Pollinators of H. verticillatus and other self-incompatible plants are likely restricted to the flight range of locally available insect visitors (Ackerman, 2000;Faegri and Leendert, 1966).…”

Genetic Diversity and Conservation Status of Helianthus verticillatus, an Endangered Sunflower of the Southern United States

“…Ellis et al (2006) rejected the hypothesis that H. verticillatus was a hybrid, thus proposing that the plant was a distinct species. Further research focusing solely on this plant found high clonal diversity, despite predominate vegetative reproduction (Mandel, 2010). Moreover, there were far fewer distinct genetic individuals than previously thought (Ellis et al, 2006;Mandel, 2010).…”

“…Further research focusing solely on this plant found high clonal diversity, despite predominate vegetative reproduction (Mandel, 2010). Moreover, there were far fewer distinct genetic individuals than previously thought (Ellis et al, 2006;Mandel, 2010). Additional studies on H. verticillatus have indicated very apparent differences in fitness among populations (Mandel, 2010;Ellis et al, 2006Ellis et al, , 2008Ellis and McCauley, 2009).…”

“…Additional studies on H. verticillatus have indicated very apparent differences in fitness among populations (Mandel, 2010;Ellis et al, 2006Ellis et al, , 2008Ellis and McCauley, 2009). These studies also posit that H. verticillatus may be more prone to self-pollination and may have experienced a major decline in distinct genetic individuals in recent history (Mandel, 2010).…”