ï~~26 THE MICHIGAN BOTANIST Vol. 38 O A. puniceus 0 A. firmus 0 00 0 0 0 0 0 4 2 16 3 6 0 0 0 2 3 0 0 ol T I 3 4 5 6 7 8 Stem Thickness (mm) 9 10 E U W U E a) 0 0 0 0 00 0 0 0 FIGURE 5. Evaluation of stem thickness, number of shoots and stem pubescence from living plants. (a) Stem thickness measured at 20 cm above the soil surface plotted against the number of shoots arising from the base of an individual plant. Points accompanied by numbers represent the number of individuals which shared identical values. (b) Stem pubescence measured at 60 cm above the soil surface plotted against stem thickness measured at 20 cm above the soil surface. 5 " " " ".1 n 3 4 5 6 7 8 Stem Thickness (mm) 9 10 and other traits, we found little evidence of introgression, leading us to suggest these taxa should be classified as two distinct species. The differences we found are particularly noteworthy since we limited our quantitative comparisons to plants that were existing in overlapping populations. If the two Asters are of the same species, cross-fertilization and intermediate forms would be expected, especially in areas where the plants co-occur (Wagner & Wagner 1983). Yet we found no evidence that supports the existence of intermediate forms, even though all the plants we evaluated were from coexisting populations. A comparison of below-ground structures of these Asters produced the most significant contrast. The stout caudex of Aster puniceus differs markedly from the extended rhizomes of A. firmus. We found that A. firmus shoots typically produce 2-6 rhizomes beginning in mid to late summer, each eventually reaching between 20-70 cm in length by late fall. To our knowledge these are the longest
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