Master of Science (MS)
Semester of Degree Completion
Gordon C. Tucker
A systematic study of the seven species of Geum L. (Rosaceae) native to Illinois including G. aleppicum var. strictum (Aiton) Fernald, G. canadense Jaquin, G. laciniatum Murray var. trichocarpum Fernald, G. rivale Linnaeus, G. triflorum Pursh, G. vernum (Rafinesque) Torrey & Gray, and G. virginianum Linnaeus is presented. Early classification systems are briefly compared, especially regarding the topic of subgenera. Detailed taxonomic descriptions, distribution information including county citations, and identification keys were developed for this study. Two seperate keys, one for floral characters and the second for specimens in fruit are given for greater ease in proper identification.
Two principal component analyses (PCA), one including vegetative and floral characteristics and another including vegetative and mature fruit characteristics, are used to illustrate the relative cohesiveness between the Illinois species. Most of the species involved show a high degree of separation in both floral and fruit studies.
Of particular interest is the relationship between Geum canadense and G. virginianum. It has been proposed that G. virginianum is a naturaly occuring hybrid between G. canadense and G. aleppicum var. strictum. In the floral study these species segregate completely, although an affinity is apparent. Mild cohesion between the clusters in the fruit study representing Geum canadense and G. virginianum does reinforce the high degree of morphological similarity between these species. Indeed in fruit the main distinguishing characteristic is that the stipules of G. virginianum are up to five times the length of those on specimens of G. canadense. There are many morphological differences between G. virginianum and G. aleppicum var. strictum. From the distributions of the proposed parents it is unlikely that G. virginianum occurs as a natural hybrid in Illinois. Geum virginianum occurs in the southern 1/4 of Illinois while G. aleppicum var. strictum occurs in the northern 2/3 of the state. These groupings conform to the currently accepted species.
Wenzel, Michael B., "A Systematic Study of the Native Geum L. species of Illinois" (1998). Masters Theses. 1685.