51. Leaves pubescent 
                    beneath; native species, rare in southern Wisconsin, mostly 
                    near streams. 
                     
                     | 
                  Morus 
                    rubra | 
                 
                 
                  51. Leaves glabrous beneath or 
                    hairs only on main veins; introduced species, invasive in 
                    disturbed sites, including drier terrestrial site. 
                     
                     | 
                  Morus 
                    alba | 
                 
               
             |