Ornamental grasses may become invasive weeds depending on their ability to naturalize and outcompete other species. Miscanthus sacchariflorus (Maxim) Franch. (Amur silvergrass) is a tall, self-incompatible, nonnative grass that has become naturalized in eastern North America, forming monospecific stands and raising concerns about its potential invasiveness. To understand the extent of clonal and sexual reproduction in feral populations, we examined their population genetic structure, seed production, and ploidy. We surveyed 21 populations in Iowa and Minnesota using eight polymorphic microsatellite markers. Only 34 multilocus genotypes (MLGs) were detected from a total of 390 samples. All of the study populations had more than one MLG, thereby allowing cross-pollination with near neighbors, but most were dominated by one or a few MLGs. Low genetic divergence suggests that all populations may have originated from similar cultivars. Cluster analysis showed that the six populations from Minnesota were extremely similar to each other, whereas the 15 populations from Iowa were somewhat more diverse. Seed production was quantified for 20 populations and ploidy for 11 populations. Average seed production was very low (< 0.30 seeds per panicle), although most populations did produce seeds. Because the populations were diploid (2x), they also may have the potential to hybridize with ornamental varieties of Miscanthus sinensis (Chinese silvergrass; eulaliagrass), a diploid close relative. Clonal growth, self-incompatibility, and spatial isolation of compatible clones may contribute to pollen-limited seed set in these populations. Low seed set may affect the rate of spread of feral M. sacchariflorus, which appears to disperse vegetatively as well as by seed. Although this species is not widely viewed as invasive, it is worth monitoring as a species that may become more widespread in the future.

Nomenclature: Amur silvergrass, silver banner grass, Miscanthus sacchariflorus (Maxim.) Franch.; Chinese silvergrass, Miscanthus sinensis Anderss.

Management Implications: Ornamental perennial grasses may have the potential to become invasive in areas where they can easily naturalize and disperse. In the nonnative genus Miscanthus, unwanted establishment of feral populations of ornamental M. sinensis (Chinese silvergrass) already has occurred in parklands and other areas, primarily in the eastern and southeastern United States. Its close relative, M. sacchariflorus (Amur silvergrass), also establishes feral populations, typically in more northern regions, but these stands are not as widespread as M. sinensis, nor do they produce abundant seeds. Low seed production could be a factor that limits population growth rates in feral M. sacchariflorus. The co-occurrence of genetically distinct individuals is a requirement for cross-pollination and seed set in this clonally reproducing, self-incompatible species. If several cross-compatible individuals occur in close proximity, this might lead to more abundant seed production and subsequent dispersal to other sites. In the current study, we found that feral populations of M. sacchariflorus in Iowa and Minnesota are genetically similar and highly clonal, but more than one genetic individual was present at each of our study sites. At present, we do not know whether M. sacchariflorus is in a temporary “lag phase” that precedes greater invasiveness. In any case, this tall, vigorously clonal perennial is able to establish extensive monospecific stands that crowd out other species, which is why managers of natural areas typically try to eradicate newly established populations. Ornamental plantings of M. sacchariflorus continue to be popular in northern areas of the United