 Disease resistance is invariably carried by the female parent.However, some of these cultivars, notably those with the Siberian elm "(Ulmus pumila)" in their ancestry, lack the forms for which the iconic American Elm and English Elm were prized.Moreover, several exported to northwestern Europe have proven unsuited to the maritime climate conditions there, notably because of their intolerance of anoxic conditions resulting from ponding on poorly drained soils in winter.