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. Dutch hybridizations invariably included the Himalayan elm "(Ulmus wallichiana)" as a source of anti-fungal genes and have proven more tolerant of wet ground; they should also ultimately reach a greater size. However, the susceptibility of the cultivar 'Lobel', used as a control in Italian trials, to elm yellows has now (2014) raised a question mark over all the Dutch clones.