ï~~28 THE MICHIGAN BOTANIST Vol. 38 28 THE MICHIGAN BOTANIST Vol. 38 TABLE 1. Values indicate the percentage of plants that exhibited each trait except for "pubescence on stem," which was scored as either dense or sparse. Pubescence A. puniceus A. firmus On midvein of cauline leaf 91% 30% On the stem 80%, dense 85%, sparse On midvein of capitulescence leaf 80% 13% In lines in capitulescence 28% 77% able, yet when we standardized stem pubescence by quantifying stem hairs at a point 60 cm above the soil surface on mature individuals, A. puniceus was found to have consistently higher values than A. firmus. Stem pubescence is commonly used to compare these plants, and it has been cited both in support of a specieslevel rank (Jones 1980b; Shinners 1941, 1946) and as evidence for intergradation (Jones 1989; Semple et al. 1983). This and other often cited overlapping characters (such as ray flower color, head size and habitat preference) are not surprising, given the high variability within many species of Aster and the apparently close relationship of these two taxa. These characters illustrate the confusion that can arise when a limited number of morphological traits from a limited portion of the plant body are utilized. We have found stem pubescence to be an important comparative trait, but suggest that it be carefully quantified and used in conjunction with a suite of other characters. In summary, by standardizing and quantifying traits that previously have been only qualitatively described and by evaluating new characters we find a clear discontinuity between plants here referred to as Aster puniceus and A. firmus. Our data show clear segregation based upon several unrelated characters and do not support the presence of intermediate forms even though all the plants used in our quantitative analyses were collected from coexisting populations (Wagner & 7066.2 Â~ A. puniceus A. firmus 60.8 600 50 e40 0 35.8 FIGURE 6. Comparison of underground S 32.4 perennating structures from 30 Aster puniceus (n=148) and A. firmus (n=68) specimens held in MICH. Rhizomes 20 mwere defined as horizontal stems greater than 5 cm in 10 length. Plants listed in the "insufficient material" cate1.5 3.4 gory either had no below0 ground material or the parts Caudex Rhizome Insufficient were too incomplete to Material assess. 0
Top of page Top of page