MORPHOMETRIC VARIATION IN OAKS OF THE APOSTLE ISLANDS IN WISCONSIN - EVIDENCE OF HYBRIDIZATION BETWEEN QUERCUS-RUBRA AND Q-ELLIPSOIDALIS (FAGACEAE)

The Apostle Islands in Lake Superior are populated by trees that are c learly related to Quercus rubra L. However, several islands have trees with morphological characteristics suggestive of hybridization with Q . ellipsoidalis Hill. Leaf specimens were collected from trees in five locations: the outermost island, an intermediate island, the nearest- shore island, the northeast shoreline, and an inland forest about 24 k m from the shoreline. Seventeen landmarks were digitized for two to fi ve leaves per tree. These landmarks were used to generate nine linear characters and three angles. These characters, along with the number o f bristle tips per leaf, were used in various combinations for several principal component analyses. In addition, the landmark configuration s were examined using rotational-fit methods. The patterns observed in both types of analysis indicate phenotypic variation coincident with a line connecting the two most distant sample sites. The location near est the geographic center of this line is also nearest the center of t he two-dimensional view of phenotypic variation. Trees at each site il lustrate a distinctive pattern in the rotational-fit analyses, and pat terns of co-variation in the morphometric characters are different for each site. The observed morphometric variation is consistent with the hypothesis that there is hybridization between these two species, mos t likely in the form of introgression from Q. ellipsoidalis into Q. ru bra.