Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

2008

Thesis Director

Gordon Tucker

Thesis Committee Member

Scott Meiners

Thesis Committee Member

Janice Coons

Abstract

Fraxinus (ash) has six species across eastern North America, five of which are found in Illinois (F. americana, F. pennsylvanica, F. nigra, F. quadrangulata, F. profimda). It is also threatened by the emerald ash borer (Agrilus planipennis) (BAB). Are climate differences across a north-south distance of 600 km great enough to create differences in the morphological characteristics of Fraxinus species? Studying latitudinal variation in the species of Fraxinus would reveal the impact of climate on the leaf characteristics of a genus of trees which extend over a considerable portion of the continent. The objectives of this study were to determine if quantitative differences occur in leaf characteristics of the species found across Illinois, to determine if EAB is present at the sites visited, to deten11ine if quantitative differences occur in leaf characteristics between variety and species for F. americana and F. pennsylvanica, and to define variation in leaf and twig characteristics for the 5 species in Illinois to see of there are any qualitative differences between the regions. Regions (northern, central, and southern Illinois) were defined using annual mean maximum and minimum temperature as well as mean total precipitation. Leaves and twigs were collected from 235 trees at 18 locations across Illinois. Materials were dried and then measured for length and width of all leaflets, leaf area and dry mass for all leaves. Data were collected for several qualitative characteristics as well. A multi variate analysis of variance and a principal components analysis were run on several characteristics for F. americana, F. pennsylvanica, F. quadrangulata, and F. profunda. Regional differences were found to be significant in F. americana and F. pennsylvanica, with total leaf area, L2 length, R2 length, T length, and L2 width, T width measurements being much larger in northern IL for white ash and leaf mass and leaf density being much larger in southern IL for green ash. Varieties were tested and F. americana var. biltmoreana was found to have significant differences from white ash, while F. pennsylvanica var. subintegerrima was not found to have significant differences. Several trees with very large leaves were found, necessitating revisions in the upper size limit for leaves of F. americana, F. nigra, and F. profunda. Two trees matching descriptions of F. caroliniana were found in Illinois. The population is most likely artificial, having arrived via unintentional introduction anytime since 1848. No signs of EAB were found at the sites in 2006. Based on the specimens of blue ash collected having several characteristics which differed from the description of the species in the literature (adaxial and abaxial leaf surface colors, leaflet shape, leaflet tip form, range of most frequent number of leaflets, leaf thickness, twig thickness, lateral bud and leaf scar size), a variety of blue ash is proposed, F. quadrangulata var. fi,scopapyraceus. Several abnormalities were observed, particularly in F. americana, indicating this species has a higher frequency of variability than previously indicated. Revised species descriptions have been provided to account for the variation seen, yet not previously described. Difficult to identify specimens were very common, with 24% having 1-2 characteristics not traditionally associated with the species it was identified to being and 8% being extremely hard to identify. These specimens refute all previously reliable wedge traits to differentiate between species ( excluding samaras). The only reliable means of discerning species is to look at a suite of characteristics, not just one or two.

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