Ulmus × hollandica Mill. , often known simply as Dutch elm, is a natural hybrid between Wych elm Ulmus glabra and field elm Ulmus minor which commonly occurs across Europe wherever the ranges of the parent species overlap. In England, according to the field-studies of R. H. Richens, "The largest area [of hybridization] is a band extending across Essex from the Hertfordshire border to southern Suffolk. The next largest is in northern Bedfordshire and adjoining parts of Northamptonshire. Comparable zones occur in Picardy and Cotentin in northern France". Crosses between U. × hollandica and either of the parent species are also classified as U. × hollandica. Ulmus × hollandica hybrids, natural and artificial, have been widely planted elsewhere.