Ulmus 'Clusius' is a Dutch hybridelmcultivar 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).
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.
^ abHeybroek, Hans M. (1983). Burdekin, D.A. (ed.). "Resistant elms for Europe"(PDF). Forestry Commission Bulletin (Research on Dutch Elm Disease in Europe) (60). London: HMSO: 108–113.
^Heybroek, H.M. (1993). "The Dutch Elm Breeding Program". In Sticklen, Mariam B.; Sherald, James L. (eds.). Dutch Elm Disease Research. New York, USA: Springer-Verlag. pp. 16–25. ISBN978-1-4615-6874-2. Retrieved 26 October 2017.
^Heybroek, H. M., Goudzwaard, L, Kaljee, H. (2009). Iep of olm, karakterboom van de Lage Landen (:Elm, a tree with character of the Low Countries). KNNV, Uitgeverij. ISBN978-90-5011-281-9
^Hiemstra, J.A.; et al. (2007). Belang en toekomst van de iep in Nederland [Importance and future of the elm in the Netherlands]. Wageningen, Netherlands: Praktijkonderzoek Plant & Omgeving B.V. Retrieved 26 October 2017.
^Burdekin, D.A.; Rushforth, K.D. (November 1996). "Elms resistant to Dutch elm disease"(PDF). Arboriculture Research Note. 2/96. Revised by J.F. Webber. Alice Holt Lodge, Farnham: Arboricultural Advisory & Information Service: 1–9. ISSN1362-5128. Retrieved 26 October 2017.
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