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Rosa multiflora Thunb. (Rosaceae), an invasive plant in the eastern U.S., was planted in the 1940's as a living fence, for wildlife cover and to prevent soil erosion. However, R. multiflora rapidly spread from these original plantings via seeds (sexual reproduction) and clonally, invading pasture and wooded areas. The purpose of this study was to determine the relative levels of asexual and sexual spread of selected R. multiflora in a pasture and park. Allozyme markers were used to determine if large (> 9 m cir.) and small (< 2 m cir.) patches of R. multiflora consisted primarily of clones or sexually reproduced plants. Larger patches of R. multiflora tended to be dominated by one genotype, but all of the patches (N=10) contained multiple unique genotypes. Six of 10 smaller patches of R. multiflora consisted of 1 Department of Entomology, Iowa State University, Ames, IA 50011 2 Corresponding author: Department of Ecology, Evolution & Organismal Biology, Iowa State University, Ames, IA 50011 3 Department of Entomology, University of Kentucky, Lexington, KY 40546 4 Department of Ecology, Evolution & Organismal Biology, Iowa State University, Ames, IA 50011 a single genotype, but 3 patches had 2 genotypes and one had 3 unique genotypes. Our results indicate that at the scale of contiguous plants (patches) R. multiflora is spreading clonally and through sexual reproduction. Although there were multiple genotypes in the large patches of R. multiflora, overall genetic diversity of large patches was consistent with clonal reproduction. Introduction The negative effects of invasive species on native species, biodiversity and ecosystem functions have been widely recognized and documented (Myers and Bazely 2003). Nonetheless, there are many non-native species in the U.S. that are not disrupting natural systems, and it is estimated that only 0.1% of all introduced species will become serious invasive species (Williamson & Fritter 1996). Life history characteristics of invasive plants are of interest to researchers because they may shed light on why certain plants are invasive and allow us to predict invasive potential before a plant is introduced into a new continent (Sakai et al. 2001). In addition, understanding the life-history characteristics of an invasive plant will provide the basis for the most effective control measures. Rosa multiflora was intentionally introduced to North America from eastern Asia in the 1940's and 50's to serve as a living fence in pastures, as a means to control soil erosion, and to provide food and cover for wildlife (Burgess 1948, Klimstra 1956). This multistemmed shrub is now invasive in eastern North America and can form impenetrable thickets that exclude native plant species and decrease pasture quality. Rosa multiflora is an insectpollinated outcrossing species; seeds are dispersed primarily by birds and rodents (Klimstra 1956, Scott 1965). It also reproduces clonally via roots and by layering (arching branches that reach the ground) (Burgess 1948, Klimstra 1956, USDA 1971). When R. multiflora was introduced to the U.S., it was presumed that seeds would germinate only under "ideal nursery conditions" and that propagation by layering would occur infrequently, when a branch was covered with soil (Burgess 1948). Consequently, invasive spread of this species was not predicted to be a problem (Steavenson 1946). Within 10 years it was apparent that R. multiflora was spreading from the original plantings and was considered to be a serious emerging problem as an invasive species (Klimstra 1956). Rosa multiflora reproduces by seeds and spreads clonally, but the relative contribution of each mode of reproduction to its spread has not been examined. Management of R. multiflora requires a reduction in both the number of plants in the area, including the seed bank, and the potential spread of these plants. Two biological control agents of R. multiflora that have the potential to reduce its spread have been examined in the United States. One is rose rosette disease (RRD), whose causative agent has not been isolated and identified, which can kill R. multiflora plants within several years (Epstein & Hill 1997). The other, Megastigmus aculeatus var. nigroflavus Hoffmeyer (Hymenoptera: Torymidae), is a wasp whose larvae develop in the seeds of R. multiflora (Weiss 1917). If sexual reproduction does not contribute significantly to the spread of R. multiflora, the wasp would have little effect on biological suppression of R. multiflora. Allozyme genetic markers have been used to determine the frequency and spatial distribution of individual plants produced sexually (via seed) or asexually (via clonal spread) (Hamrick et al. 1979). In our study we used allozyme methods to quantify the relative levels of R. multiflora spread by seed dispersal and clonal growth within two habitats: woodland parks and open pastures. In the park setting we expected a significant contribution to spread

The biology of Rosa multiflora (Rosaceae) and two of its biotic mortality factors