/ Evidence for a Species-Level Distinction of Two Co-occurring Asters: Aster Puniceus L. And Aster Firmus Nees
ï~~1999 THE MICHIGAN BOTANIST 19 EVIDENCE FOR A SPECIES-LEVEL DISTINCTION OF TWO CO-OCCURRING ASTERS: ASTER PUNICEUS L. AND ASTER FIRMUS NEES David P. Warners and Daniel C. Laughlin Biology Department Calvin College 3201 Burton SE Grand Rapids, MI 49546 (616) 957-6820 ABSTRACT We examined the possibility that two co-occurring wetland asters, commonly referred to as Aster puniceus var. puniceus and A. puniceus var. firmus, are sufficiently distinct to be segregated at the species level. In our study of collected and field specimens we limited our research to 10 study sites in southern Michigan where both asters coexist. We assumed that if the two taxa belong to one species, gene flow (and hence, intermediate forms) will most likely occur in locations where they grow together (Wagner & Wagner 1983). By quantifying previously-cited characters and new comparative traits of below-ground parts, above-ground vegetative characteristics and capitulescence architecture, we found no evidence of intergradation between these coexisting populations. Therefore, we conclude that the most appropriate taxonomic treatment of these asters is to recognize a specieslevel designation: Aster puniceus L. and Aster firmus Nees. INTRODUCTION The notoriously difficult genus Aster has provided plant taxonomists fertile ground for inquiry and debate (Jones 1980a, 1980b, 1989; Nesom 1994; Semple et al. 1983, Semple et al. 1996; Shinners 1941,1946; Van Faasen 1963; Wiegand 1924). Asa Gray, the renowned 19th century botanist, lamented, I am half dead with Aster... If you hear of my breaking down utterly, and being sent to an asylum, you may lay it to Aster, which is a slow and fatal poison (quoted in Semple 1987). Further illustration of the complexity and promiscuity of these taxa has been voiced by Dr. Arthur Cronquist: If complete morphological discontinuity were the sole criterion for the acceptance of species in this group, they could all be reduced to one species (Cronquist 1943). Such confusion is well represented in the swamp aster (Aster puniceus L.). Aster puniceus (sensu lato) is typically classified under the subgenus Symphyotrichum (Nees) A. G. Jones, section Salicifolii Torrey & A. Gray, and subsection Leucanthi (Nees) A. G. Jones (Jones 1980a). However, recent taxonomic work suggests the genus Aster be separated into 13 distinct genera and that the taxon of this study be classified within the newly proposed genus Symphyotrichum (Nesom 1994). However, since the foundational literature this study is based upon uses the
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