Undergraduate Research Symposium Poster Presentation


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Undergraduate Research Symposium Poster Presentation

  1. 1. SummaryThe North American plant genus Packera is a member of theAsteraceae (Sunflower Family). Most of the approximately 70Packera species are morphologically distinct and occur in differentgeographic areas or microhabitats. However, populations of thewidespread, P. paupercula (Michaux) Å. Löve & D. Löve complexare variable in morphology, chromosome number, and ecologicalrequirements. A species complex often serves as a “grab bag”for very similar groups of populations that have not yet beenformally recognized as distinctive taxa. One undescribed group oftetraploid populations currently recognized in P. paupercula occursin north central North America, including northern Minnesota.These “northern tetraploids” may merit recognition at the species orvarietal level.Northern tetraploids are similar in morphology to Packeraplattensis, 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. pauperculacomplex in our region,. As part of a larger study that seeks todescribe and classify the northern tetraploids, I measuredcharacters on herbarium specimens that included six Packera taxa.I used one-way analysis of variance (ANOVA) with the FisherLeast Significant Difference (LSD) test to determine whichcharacters best differentiate the taxa. Of particular interest wasfinding morphological characters that differentiate the northerntetraploids from P. plattensis, which are often confused with oneanother.Finding characters that will differentiate two very similarPackera (Ragwort) taxa in the Upper MidwestErika Magnusson and Alison Mahoney, PhDResultsOf the 17 characters tested, seven showed at least one significantdifference between character means in pairwise comparisons among sixPackera taxa (Table 1). Six of the seven characters were useful indistinguishing P. paupercula “northern tetraploids” from P. plattensis. Theywere 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), andthe ratio of basal leaf blade length/basal leaf length-to-center (p < 0.003)(Figure 3).AcknowledgementsWe are grateful to the following herbaria for specimen loans: DUL, MIN,and WIS and to the Radichel Family Foundation for providing funds tosupport research in the Darlene & William Radichel Herbarium and to printthis poster. Funding for the purchase of the reticules was provided by theMSU-Mankato Honors Program.Literature CitedBarkley, 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 inWisconsin. Rhodora 65: 65--67.Funk, V.A., A. Susanna, T.F. Stuessy, and R.J. Bayer. 2009. Systematics, evolution andbiogeography of compositae. Vienna, International Association for Plant Taxonomy, pp385-410.Kowal, R. R. 1975. Systematics of Senecio aureus and allied species on the GaspéPeninsula, 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 EditorialCommittee (editors), Flora of North America North of Mexico, Vol. 20. Oxford UniversityPress, New York.BackgroundObjectiveThe most important objective of this study was to learn what field-observable characters best distinguish among the “northerntetraploids” and Packera plattensis, which both occur in northernMinnesota and have traditionally been confused because bothare pubescent.MethodsI measured 13 morphological characters and recorded the floweringdate on 82 herbarium specimens. I used a dissecting microscopewith an ocular micrometer for measurements to the heads, a 10 cmruler 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 withMay 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 ratiosusing basal leaf measurements.Table 1 gives characters, their abbreviations, units, and ANOVA testswith significant results. Figure 1 and Figure 2 show diagrams withmeasurements indicated.Data Analysis I used analysis of variance (ANOVA) on SigmaPlot(Systat Software) to determine which characters or character ratiosbest distinguish six Packera taxa. This poster focuses on results forcomparisons between P. plattensis and the northern tetraploids.Morphological characters: Taxonomists have traditionally usedmorphological characters provided by reproductive structures(flowers, fruits, cones, etc.) and vegetative characters such as leafarrangement and shape, to differentiate among plant taxa. Packerais a member of the sunflower family that is characterized by havingsmall flowers arranged in dense inflorescences called “heads” (Fig.1) (Funk et al. 2009). Floral characteristics are not very useful whendistinguishing among Packera species because their heads are allvery similar; instead, vegetative characters such as leaf shape andpubescence (hairiness), underground reproductive structures, andecological requirements have been used (Barkley 1962; Mahoney& Kowal 2008).Cytological characters (chromosome base number and ploidylevel): With the advent of chromosome counting in the 1940s and‘50s, it was discovered that Packera species have two basechromosome numbers, x = 22 and x = 23 (Kowal 1975; Trock 2006).While many Packera taxa are diploid (having two sets ofchromosomes), polyploid formation (the spontaneous doublingof chromosome sets) also occurs frequently in Packera. Tetraploidshave four sets chromosomes; hexaploids have six sets. Cytologicalcharacters are important for distinguishing Packera groups.However, these characters cannot be used in the field to identifytaxa.Similar pubescent (hairy) Packera taxa in our area: Packeraplattensis (Nuttall) W. A. Weber & Å. Löve is a more-or-lesspermanently pubescent tetraploid species with x = 23 occurring inprairie or prairie-like habitats throughout the Great Plains.Traditionally, P. paupercula has been described as glabrous (withouthairs). To account for a series of morphologically intermediate,pubescent populations in western Wisconsin and southernMinnesota, Barkley (1962, 1963) suggested that P. plattensis and P.paupercula were hybridizing. Cytological assays indicate that the basechromosome number for P. paupercula east of the GreatPlains is x = 22 so hybridization between these two specieswould be unlikely (Kowal 1975, unpublished ms). Mahoney and Kowal(2008) named and described two groups of these pubescentpopulations with x = 22 as varieties of P. paupercula. They can beidentified by their distinctive underground reproductive structures.The “northern tetraploids:” Kowal’s extensive chromosome countsin Packera indicate there are tetraploid populations in northernMinnesota 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 willbe undertaken to confirm chromosome numbers and to learn moreabout the life history, ecological requirements, and geographicdistribution of these populations. They may merit recognition as a newspecies or as a variety of P. paupercula. It is vital that morphologicalcharacters be found to differentiate between P. plattensis and thenorthern 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 givingthe name of the plant and where, when, and by whom it was collected.I made measurements on specimens from the Darlene & WilliamRadichel Herbarium at Minnesota State University-Mankato (MANK),the Bell Museum of Natural History Herbarium at the University ofMinnesota-St. Paul (MIN), the Olga Lakala Herbarium at the Universityof Minnesota-Duluth (DUL), and the Wisconsin State Herbarium at theUniversity of Wisconsin-Madison (WIS).ConclusionsWhile no one character was useful in discriminating among all six Packerataxa, seven of 17 characters were useful. Six of the seven characters willbe useful in discriminating between P. plattensis and the northerntetraploids in the field. Naming a new species or variety requirespublication that includes a thorough morphological description and a key torelated species. My work provides a foundation for this component of thepublication process.Figure 1. Measurements made toplants preserved as herbariumspecimens. BL LTC measures thedistance from the base of the leafblade to its widest part. "Illustration:Packera paupercula." Flora of NorthAmerica. eFlora, n.d. Web. 10 Apr.2013. <www.efloras.org>Figure 2. Measurements made toheads and secondary inflorescences.Packera paupercula. University ofMassachusetts Herbarium, Amherst.Web. 10 Apr. 2013.012345678910INV L (mm) R L (mm) BL LTC (cm) HT (dm)CharacterMeanFigure 3. Mean values for four of six characters that differed significantlybetween Packera paupercula “northern tetraploids” (orange bars) and P.plattensis (green bars). Error bars indicate standard errors. Characterswere tested using one-way ANOVAs; pairwise comparisons were testedusing the Fisher LSD method at  = 0.05.Table 1. Characters, character abbreviations, and units measuredon 82 herbarium specimens of six Packera taxa and tested by one-way ANOVA. Character means with at least one pairwisesignificant difference are indicated by asterisks in column 4.(Figure 1. and Figure 2.)