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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.
