Background/Question/Methods
Polyploidy is a type of genetic variation in which an individual can have more than two complete sets of chromosomes.  Conspecific plants with different numbers of chromosomes can differ in morphology, physiology, communities of pollinators and herbivores, phenology of flowering, and other life history traits.  Thus, polyploidy can be a mechanism that results in sympatric speciation through genetic and ecological divergence.  I investigated the distribution of diploid, autotetraploid, and autohexaploid plants of the species Solidago altissima L. (Asteraceae) in Illinois to test the hypothesis that if cytotypes of S. altissima are undergoing sympatric speciation as a result of ecological divergence, then they should inhabit different microhabitats, differ in phenotype, and be differentially attacked by herbivorous insects.

Results/Conclusions
All three cytotypes of S. altissima were present at most of my ten study sites in east-central and northeastern Illinois, but ramets of different cytotype inhabited different microhabitats.  Diploids tended to grow in open areas far from trees and other woody plants where they were surrounded by grasses and high species richness of herbaceous plants, tetraploids grew in areas with slightly more shade and were surrounded by less grass and lower species richness, and hexaploids grew in proximity to trees and other woody plants where grasses were not dominant.  These differences in microhabitat could be influenced by competitive interactions among cytotypes or with other plant species, differences in dispersal ability, edaphic factors, or even herbivores that vary in abundance across microhabitats.  Morphology also varied with cytotype: hexaploids were taller than diploids and tetraploids and had more leaves that were longer and wider.  However, none of these morphological traits differed with cytotype in a common garden, suggesting that morphology is determined by environmental factors that differ across microhabitats rather than cytotype alone.  Seven species of herbivores were common on goldenrod, and two, the leaf galler Asteromyia carbonifera (Osten Sacken) and the aphid Uroleucon nigrotuberculatum (Olive), were most abundant on hexaploids.  However, all herbivores were evenly distributed across cytotypes of S. altissima within a common garden, suggesting that cytotype alone does not determine the abundance of herbivores on individual ramets.  Despite these similarities within a common garden, this is a system in which sympatric speciation may result from ecological divergence among cytotypes.