Michael L. Scott Jonathan M. Friedman Richard D. Laven Patrick B. Shafroth 1994 Several Eurasian tree willows (<i>Salix</i> spp.) have become naturalized in riparian areas outside of their native range. <i>Salix x rubens</i> is a Eurasian willow that is conspicuous along streams in the high plains of Colorado. We examined establishment of seedlings and cuttings, the sex structure and the breeding system of <i>S. x rubens</i>. An experiment was conducted on establishment and growth of seedlings and cuttings under a range of hydrologic conditions. Seedlings became established under all conditions except when flooded, although many fewer seedlings became established where soil surface conditions were relatively dry. Cuttings became established under all experimental conditions, but most frequently where soil moisture was highest. The sex structure of <i>S. x rubens</i> was determined along several streams in the Colorado high plains. Of 2175 trees surveyed, >99% (2172) were female. <i>Salix x rubens</i> produce viable seed apparently as a result of hybridization with another Eurasian willow, <i>S. alba</i> var. <i>vitellina</i>. <i>Salix x rubens</i> often reproduces vegetatively, which, combined with low hybrid seedling survival in the field, may explain the unusual sex structure. <i>Salix x rubens</i> will likely continue to spread vegetatively in high plains riparian areas, and the potential for spread through hybridization could increase if males of compatible <i>Salix</i> spp. are planted near extant <i>S. x rubens</i>. application/pdf 10.2307/2426210 en University of Notre Dame Establishment, sex structure and breeding system of an exotic riparian willow, Salix X rubens article