This study aimed to identify morphological characters that differentiate the northern tetraploid Packera taxa from P. plattensis in Minnesota, as the two are often confused. The author measured 13 characters on 82 herbarium specimens of 6 Packera taxa. ANOVA found 7 characters with significant mean differences, including flowering date, involucre length, ray length, basal leaf length-to-center, height, and two ratios. Of these, 6 characters effectively distinguished the northern tetraploids from P. plattensis. Identifying these differentiating characters provides a foundation for formally recognizing and describing the northern tetraploid group.

1. Summary
The North American plant genus Packera is a member of the
Asteraceae (Sunflower Family). Most of the approximately 70
Packera species are morphologically distinct and occur in different
geographic areas or microhabitats. However, populations of the
widespread, P. paupercula (Michaux) Å. Löve & D. Löve complex
are variable in morphology, chromosome number, and ecological
requirements. A species complex often serves as a “grab bag”
for very similar groups of populations that have not yet been
formally recognized as distinctive taxa. One undescribed group of
tetraploid populations currently recognized in P. paupercula occurs
in north central North America, including northern Minnesota.
These “northern tetraploids” may merit recognition at the species or
varietal level.
Northern tetraploids are similar in morphology to Packera
plattensis, a tetraploid prairie species found in western Minnesota,
P. pseudaurea var. semicordata, a hexaploid species found in wet,
open habitats, and to other diploid members of the P. paupercula
complex in our region,. As part of a larger study that seeks to
describe and classify the northern tetraploids, I measured
characters on herbarium specimens that included six Packera taxa.
I used one-way analysis of variance (ANOVA) with the Fisher
Least Significant Difference (LSD) test to determine which
characters best differentiate the taxa. Of particular interest was
finding morphological characters that differentiate the northern
tetraploids from P. plattensis, which are often confused with one
another.
Finding characters that will differentiate two very similar
Packera (Ragwort) taxa in the Upper Midwest
Erika Magnusson and Alison Mahoney, PhD
Results
Of the 17 characters tested, seven showed at least one significant
difference between character means in pairwise comparisons among six
Packera taxa (Table 1). Six of the seven characters were useful in
distinguishing P. paupercula “northern tetraploids” from P. plattensis. They
were flowering date (p < 0.001), involucre length (p < 0.001), ray length (p
< 0.014), basal leaf length-to-center (p < 0.011), height (p < 0.003), and
the ratio of basal leaf blade length/basal leaf length-to-center (p < 0.003)
(Figure 3).
Acknowledgements
We are grateful to the following herbaria for specimen loans: DUL, MIN,
and WIS and to the Radichel Family Foundation for providing funds to
support research in the Darlene & William Radichel Herbarium and to print
this poster. Funding for the purchase of the reticules was provided by the
MSU-Mankato Honors Program.
Literature Cited
Barkley, T. M. 1962. A revision of Senecio aureus Linn. and allied species. Trans. Kans.
Acad. Sci. 65: 318--408.
___. 1963. The intergradation of Senecio plattensis and Senecio pauperculus in
Wisconsin. Rhodora 65: 65--67.
Funk, V.A., A. Susanna, T.F. Stuessy, and R.J. Bayer. 2009. Systematics, evolution and
biogeography of compositae. Vienna, International Association for Plant Taxonomy, pp
385-410.
Kowal, R. R. 1975. Systematics of Senecio aureus and allied species on the Gaspé
Peninsula, Quebec. Mem. Torrey Bot. Club 23: 1--113.
___ & C. C. Freeman. Unpubl. ms. Chromosome numbers of the genus Packera
(Asteraceae: Senecioneae): a summary.
Mahoney, A.M. & R.R. Kowal. 2008. Three new varieties of Packera paupercula
(Asteraceae, Senecioneae) in midwestern and southeastern North America. Novon 18:
220-228.
Trock, D. K. 2006. Packera. Pp. 570–602 in Flora of North America Editorial
Committee (editors), Flora of North America North of Mexico, Vol. 20. Oxford University
Press, New York.
Background
Objective
The most important objective of this study was to learn what field-
observable characters best distinguish among the “northern
tetraploids” and Packera plattensis, which both occur in northern
Minnesota and have traditionally been confused because both
are pubescent.
Methods
I measured 13 morphological characters and recorded the flowering
date on 82 herbarium specimens. I used a dissecting microscope
with an ocular micrometer for measurements to the heads, a 10 cm
ruler for most vegetative characters, and a 30 cm ruler for height.
To measure cauline apical leaf angle (CLAA) I used a 25 mm angle-
measure reticle. To analyze differences among flowering dates,
dates were recorded in days of May such that numbering starts with
May 1 and continues through the rest of the growing season, i.e.
June 1 = May 32, June 2 = May 33, etc. I also created three ratios
using basal leaf measurements.
Table 1 gives characters, their abbreviations, units, and ANOVA tests
with significant results. Figure 1 and Figure 2 show diagrams with
measurements indicated.
Data Analysis I used analysis of variance (ANOVA) on SigmaPlot
(Systat Software) to determine which characters or character ratios
best distinguish six Packera taxa. This poster focuses on results for
comparisons between P. plattensis and the northern tetraploids.
Morphological characters: Taxonomists have traditionally used
morphological characters provided by reproductive structures
(flowers, fruits, cones, etc.) and vegetative characters such as leaf
arrangement and shape, to differentiate among plant taxa. Packera
is a member of the sunflower family that is characterized by having
small flowers arranged in dense inflorescences called “heads” (Fig.
1) (Funk et al. 2009). Floral characteristics are not very useful when
distinguishing among Packera species because their heads are all
very similar; instead, vegetative characters such as leaf shape and
pubescence (hairiness), underground reproductive structures, and
ecological requirements have been used (Barkley 1962; Mahoney
& Kowal 2008).
Cytological characters (chromosome base number and ploidy
level): With the advent of chromosome counting in the 1940s and
‘50s, it was discovered that Packera species have two base
chromosome numbers, x = 22 and x = 23 (Kowal 1975; Trock 2006).
While many Packera taxa are diploid (having two sets of
chromosomes), polyploid formation (the spontaneous doubling
of chromosome sets) also occurs frequently in Packera. Tetraploids
have four sets chromosomes; hexaploids have six sets. Cytological
characters are important for distinguishing Packera groups.
However, these characters cannot be used in the field to identify
taxa.
Similar pubescent (hairy) Packera taxa in our area: Packera
plattensis (Nuttall) W. A. Weber & Å. Löve is a more-or-less
permanently pubescent tetraploid species with x = 23 occurring in
prairie or prairie-like habitats throughout the Great Plains.
Traditionally, P. paupercula has been described as glabrous (without
hairs). To account for a series of morphologically intermediate,
pubescent populations in western Wisconsin and southern
Minnesota, Barkley (1962, 1963) suggested that P. plattensis and P.
paupercula were hybridizing. Cytological assays indicate that the base
chromosome number for P. paupercula east of the Great
Plains is x = 22 so hybridization between these two species
would be unlikely (Kowal 1975, unpublished ms). Mahoney and Kowal
(2008) named and described two groups of these pubescent
populations with x = 22 as varieties of P. paupercula. They can be
identified by their distinctive underground reproductive structures.
The “northern tetraploids:” Kowal’s extensive chromosome counts
in Packera indicate there are tetraploid populations in northern
Minnesota and Wisconsin with x = 22 (Kowal, pers. comm.,
unpublished ms.). Because many of these populations are pubescent,
they have been and continue to be misidentified as P. plattensis.
Currently, this group of populations is undescribed. More studies will
be undertaken to confirm chromosome numbers and to learn more
about the life history, ecological requirements, and geographic
distribution of these populations. They may merit recognition as a new
species or as a variety of P. paupercula. It is vital that morphological
characters be found to differentiate between P. plattensis and the
northern tetraploids so they can be correctly identified in the field.
Use of herbarium specimens: Herbaria are collections of dried,
pressed plant specimens mounted on heavy paper with labels giving
the name of the plant and where, when, and by whom it was collected.
I made measurements on specimens from the Darlene & William
Radichel Herbarium at Minnesota State University-Mankato (MANK),
the Bell Museum of Natural History Herbarium at the University of
Minnesota-St. Paul (MIN), the Olga Lakala Herbarium at the University
of Minnesota-Duluth (DUL), and the Wisconsin State Herbarium at the
University of Wisconsin-Madison (WIS).
Conclusions
While no one character was useful in discriminating among all six Packera
taxa, seven of 17 characters were useful. Six of the seven characters will
be useful in discriminating between P. plattensis and the northern
tetraploids in the field. Naming a new species or variety requires
publication that includes a thorough morphological description and a key to
related species. My work provides a foundation for this component of the
publication process.
Figure 1. Measurements made to
plants preserved as herbarium
specimens. BL LTC measures the
distance from the base of the leaf
blade to its widest part. "Illustration:
Packera paupercula." Flora of North
America. eFlora, n.d. Web. 10 Apr.
2013. <www.efloras.org>
Figure 2. Measurements made to
heads and secondary inflorescences.
Packera paupercula. University of
Massachusetts Herbarium, Amherst.
Web. 10 Apr. 2013.
0
1
2
3
4
5
6
7
8
9
10
INV L (mm) R L (mm) BL LTC (cm) HT (dm)
Character
Mean
Figure 3. Mean values for four of six characters that differed significantly
between Packera paupercula “northern tetraploids” (orange bars) and P.
plattensis (green bars). Error bars indicate standard errors. Characters
were tested using one-way ANOVAs; pairwise comparisons were tested
using the Fisher LSD method at  = 0.05.
Table 1. Characters, character abbreviations, and units measured
on 82 herbarium specimens of six Packera taxa and tested by one-
way ANOVA. Character means with at least one pairwise
significant difference are indicated by asterisks in column 4.
(Figure 1. and Figure 2.)