Ulmus × intermedia 'Coolshade'

The hybrid elm cultivar Ulmus × intermedia 'Coolshade' is an American hybrid cultivar cloned from a crossing of the Slippery, or Red, Elm Ulmus rubra (female parent) and the Siberian Elm Ulmus pumila at the Sarcoxie Nurseries, Sarcoxie, Missouri, in 1946. At Arnold Arboretum, where there was a specimen, herbarium material was labelled Ulmus pumila 'Coolshade'.^[1]

Ulmus × intermedia 'Coolshade'
Hybrid parentage	U. rubra × U. pumila
Cultivar	'Coolshade'
Origin	Sarcoxie, Missouri, USA

Description

'Coolshade' has rapid, stocky growth with a compact crown resistant to breakage under ice and snow. Its foliage is a very dark green.^[2][3] There appears to be little evidence of Ulmus rubra ingression in the Arnold Arboretum 1960 leaves specimens labelled Ulmus pumila 'Coolshade', suggesting that its hybridity may have been questioned there.^[4]

Pests and diseases

Reputedly tolerant of Dutch elm disease, 'Coolshade' has not been tested by inoculation to determine the degree of resistance.

Cultivation

'Coolshade' was raised to create a disease-resistant tree that would not suffer the storm damage frequently sustained by the weak-wooded U. pumila. The tree was introduced to the UK in the 1960s but no longer survives there.

Cultivars

• 'Improved Coolshade'

Accessions

North America

• Arnold Arboretum, US. Acc. no. 561–48

References

1. "Herbarium specimen - L.1582543". Botany catalogues. Naturalis Biodiversity Center. Sheet labelled U. pumila L. 'Coolshade' (Arnold Arboretum specimen 1, 1960); "Herbarium specimen - WAG.1911576". Botany catalogues. Naturalis Biodiversity Center. Sheet labelled U. pumila L. 'Coolshade' (Arnold Arboretum specimen 2, 1960)
2. Green, Peter Shaw (1964). "Registration of cultivar names in Ulmus". Arnoldia. Arnold Arboretum, Harvard University. 24 (6–8): 41–80. Retrieved 16 February 2017.
3. Bean, W. J. (1981). Trees and shrubs hardy in Great Britain, 7th edition. Murray, London.
4. bioportal.naturalis.nl, specimen L.1582543