Ulmus 'Sapporo Autumn Gold'

Ulmus hybrid cultivar
'Sapporo Autumn Gold' at Antella, Florence, believed to be the largest in Europe.
Hybrid parentage	U. davidiana var. japonica × U. pumila
Cultivar	'Sapporo Autumn Gold'
Origin	seeds: Sapporo, Japan; cultivated: United States

Ulmus 'Sapporo Autumn Gold' is one of the most commercially successful hybrid elm cultivars ever marketed, widely planted across North America and western Europe, although it has now been largely supplanted by more recent introductions. Arising from a chance crossing in 1958 of the Japanese elm (Ulmus davidiana var. japonica) (female parent) and Siberian elm (Ulmus pumila) in the Botanical Garden of Hokkaido University, Sapporo, it was cultivated at the University of Wisconsin–Madison by Eugene Byron Smalley. The patent issued in 1975 has expired, and there are now no propagation restrictions.

The tree usually forks at 1.5–2 m from the ground to produce a broad, rounded, densely foliated crown, although immature plants produce vigorous side shoots requiring assiduous pruning to maintain shape. The bark is pale grey, and longitudinally fissured to form a random lattice pattern. The leaves are narrowly elliptical, < 9 cm long by < 4.5 cm wide, with 8 mm petioles. As the name implies, the leaves turn pale yellow in autumn. The perfect, apetalous wind-pollinated flowers appear in early March, followed by the seeds in April; flowering usually begins when the tree is aged six years.

Bark of 30-year-old tree

Foliage

Coastal tree, Mudeford, UK

Tree left unpruned

'Sapporo Autumn Gold' possesses a very high resistance to Dutch elm disease; in trials in Italy, it sustained only 2.8% defoliation and 1.2% dieback when inoculated with unnaturally high concentrations of the fungal pathogen.[5] The cultivar also has a tolerance of Verticillium wilt. The tree's foliage was adjudged 'resistant' to black spot by the Plant Diagnostic Clinic of the University of Missouri [6], however it can be severely damaged by the elm leaf beetle (Xanthogaleruca luteola) in the United States [7] Several mature specimens near the Hampshire coast in England have become (2014) afflicted by Dryad's saddle fungus (Polyporus squamosus).