ï~~1999
THE MICHIGAN BOTANIST
29
Wagner 1983). We conclude that the most appropriate taxonomic treatment of
these two asters is a species-level separation.
This study also identifies the need for additional research on these taxa. Our
interpretation of the numerous treatments which have failed to recognize a
species-level distinction is that a few overlapping characters (stem pubescence,
ligule color, and habitat) have been emphasized, while other more definitive
characters (particularly below-ground structures) have been overlooked. However, we acknowledge the possibility that these asters behave as distinct species
in a portion of their range (including southern Michigan), but may intergrade in
other areas, as reported by Jones (1984). Our assessment of herbarium material
did not support this phenomenon, but future quantitative research on populations
outside the range covered in this study will more confidently evaluate this possibility. Further research that assesses phenotypic plasticity (possibly with additional characters such as capitulescence bract size, capitulescence bract biomass,
floral characters, involucral bract traits, etc.) using controlled pollination experiments, as well as molecular techniques, will also contribute to a more detailed
understanding of the relatedness of these two asters.
KEY TO ASTER PUNICEUS AND A. FIRMUS
1. Stems densely pubescent, usually purplish; abaxial cauline leaf midvein moderately to densely pubescent; capitulescence widely spreading and heads with
lavender to purple ray florets; shoots often found in clumps of 2-6 arising
from a persistent stout caudex................................................ Aster puniceus.
1. Stems glabrous, occasionally hispidulous in lines; abaxial cauline leaf midvein glabrous; capitulescence dense, leafy; heads with white to pale lavender
ray florets; shoots arising singly from elongate rhizomes.......... Aster firmus.
DESCRIPTIONS OF THE SPECIES
Aster puniceus L. Sp. P1. 875. 1753.
'Swamp Aster,' 'Purple-stemmed Aster'
Herbaceous perennial with several new shoots emerging annually from a single
stout caudex. Stems relatively broad near base (5-11 mm diameter), erect,
50-200 cm tall, usually uniformly anthocyanotic (Semple & Heard 1987). Pubescence on stem densely hirsute, 10-30 hairs per 25 mm2; pubescence in capitulescence moderately dense, occasionally in lines decurrent from nodes.
Leaves of winter-rosettes large (Jones 1980b; Gleason and Cronquist 1991),
basal leaves commonly deciduous at anthesis. Cauline leaves alternate, 10-22
cm long, 3-4 cm wide at widest point, dark green (Semple 1983), margins
crenate-serrate, elliptic to oblanceolate, auriculate clasping; abaxial midvein
moderately to densely hispid (5-10 hairs/ mm near leaf base). Capitulescence
open, lax, paniculiform with widely spreading heads. Leaves in capitulescence
