[1] As Red Elm U. rubra is far less fertile, and highly susceptible to Dutch elm disease (:DED), it could eventually be hybridized out of existence by U.
[2] The hybrid was first reported from the wild in the Chicago region in 1950 and was provisionally named U.
[3] The horticulture industry made a number of artificial crosses of the two species, such as 'Coolshade' and 'Fremont', in an attempt to create ornamental trees resistant to DED.
[1] Ulmus × intermedia is significantly different from both parental species, except in biometrics such as leaf length to width ratios, number of teeth, petiole length, and pollen size.
[1][4] Atypically, fertility of the hybrid seed is high, occasionally in excess of 90%,[5] while Collins found in artificial hybridization no reduction of fertility in the F1 or F2 generations.