Ulmus 'Clusius'

Ulmus 'Clusius' is a Dutch hybrid elm cultivar raised at the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen, as clone 568^[1] and released to commerce in 1983. 'Clusius' was derived from a crossing of the same Dutch clones that produced the fastigiate 'Lobel' released in 1973: '202' ('Exoniensis' × U. wallichiana) and '336' ('Bea Schwarz' selfed).

Ulmus 'Clusius'
Ulmus 'Clusius', Netherlands.
Genus	Ulmus
Hybrid parentage	('Exoniensis' × U. wallichiana) × 'Bea Schwarz' selfed
Cultivar	'Clusius'
Origin	Wageningen, The Netherlands

Description

The tree has a broader crown than its sibling's, whilst the generally obovate leaves, < 11 cm long by 7 cm wide, are less acuminate at the apex and a lighter green. The seed is near the notch (apex) of the samara.^[1][2] Like 'Lobel', the tree flushes markedly later than most other elms, and is rarely in full leaf before mid-May.

Pests and diseases

Whilst the resistance of 'Clusius' to Dutch elm disease proved marginally greater than that of its Dutch predecessors, rated 4 out of 5,^[3] it has been eclipsed by later developments such as Lutèce. Consequently, sales in the Netherlands declined from over 8,000 in 1979 to 600 in 2004.^[4]

Cultivation

While 'Clusius' remains for sale in Europe, its planting where the disease remains prevalent cannot be recommended.^[5] In the UK, 'Clusius' is present in the National Elm Collection, Brighton and Hove,^[6] and in Edinburgh (two in Abbeyhill, opposite Holyrood Palace,^[7] and one in The Meadows^[8]). Six specimens were planted in front of the library, Keele University, Staffordshire, c.2010.^[9][10] 'Clusius' featured in New Zealand government trials during the 1990s at the Hortresearch station, Palmerston North, but is not known to have been introduced to North America.

• 
  'Clusius', Medemblik train station (2013)
• 
  Six 'Clusius' in Union Square, Keele University (2015)
• 
  Same, 2018

Etymology

The cultivar is named for Carolus Clusius, a Dutch naturalist of the Renaissance.

Accessions

Europe

• Arboretum de La Petite Loiterie , Monthodon, France. No details available
• Grange Farm Arboretum, Sutton St James, Spalding, Lincs., UK. Acc. no. 817.
• Sir Harold Hillier Gardens, Ampfield, Romsey, Hampshire, UK. Acc. no: 2019.0441
• Wijdemeren City Council, Netherlands. Elm Collection. planted mainly in Kortenhoef since 2006.

Nurseries

• Noordplant , Glimmen, Netherlands.
• Barcham Trees PLC, Ely, Cambridgeshire.