Taxonomic, ecologic, and biogeographic studies in Polymnia (Asteraceae)

Background/Question/Methods

The genus Polymnia L. (Asteraceae: Tribe Polymnieae) is endemic to temperate, deciduous forests of eastern North America and currently includes four robust, herbaceous species (P. canadensis, P. cossatotensis, P. laevigata, and P. johnbeckii). This is a group that has remained unresolved due to confusion surrounding interspecific and infraspecific taxonomy, especially with regards to the widespread P. canadensis; a species that inhabits rocky, calcareous woods throughout most of eastern North America. Varieties and forms within the species have been recognized based on distinctive morphological characteristics such as ligule length, achene morphology, and pubescence. This study seeks to determine whether there are morphological entities within P. canadensis that correspond with geographic trends or whether the variation within P. canadensis is continuous without correlation to geography. Several hundred specimens of P. canadensis were borrowed and critically examined for morphological variation. In order to quantify variation, 65 plants were measured for 44 discrete and continuous characters. Principle Components Analysis (PCA) was used to visualize separation between distinct groups within P. canadensis and identify the morphological variables which best diagnose these groups. To examine geographic trends, data obtained through herbarium specimens were used to plot distributions of distinct morphological groups on an outline map.

Results/Conclusions

Results from the morphological analysis and PCA indicate the presence of at least three distinct morphological entities within P. canadensis that correlate with geographic trends. Based on these results, we have determined that P. canadensis is most likely a complex composed of several species or subspecies. A distinct morphological variant that is characterized by possessing a combination of glandular-puberulent and eglandular septate trichomes on the stems and leaves, and large, showy rays has been identified to be typical of the Interior Highlands region. Another morphological variant has been identified from the Interior Low Plateau and is characterized by glabrous stems, and small-medium ray florets. A more widely distributed type has been identified as typical of the northern United States and is characterized by possessing eglandular septate trichomes on the stems and leaves, and small ray florets. Further statistical analyses are needed to assist in delineating any other morphological entities and determining the level of taxonomic recognition for these entities.