Ulmus × intermedia explained

Ulmus × intermedia
Hybrid:U. pumila × U. rubra
Origin:US

Ulmus × intermedia Elowsky is a natural hybrid elm occurring across Nebraska and several other Midwestern states, derived from the crossing of Ulmus rubra and Ulmus pumila.[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. × intermedia.[2] The hybrid was first reported from the wild in the Chicago region in 1950 and was provisionally named U. × notha Wilhelm & Ware in 1994.[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]

Description

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. The leaves are 4.5 - 12 × 2.5 - 6  cm, petiole 0.3 × 1.2  cm, ovate to lanceolate, apex acuminate to acute, base oblique. The samarae are 11.5 - 21.0 × 10.0 - 20.0 mm, cream to white.[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.[6]

Pests and diseases

Morton Arboretum report the hybrid susceptible to DED and Elm Yellows (Elm phloem necrosis).

Cultivation

Specimens of unnamed Ulmus × intermedia (= Ulmus × notha) stand (2015) in Morton Arboretum, Illinois, received as Ulmus pumila from North Platte Agricultural Experiment Station, University of Nebraska.[7] [8] [9]

Cultivars

'Hamburg' may also belong to the Ulmus × intermedia group.[10]

Notes and References

  1. Elowsky. C.G.. Jordon-Thaden. I.E.. Kaul. R.B.. A morphological analysis of a hybrid swarm of native Ulmus rubra Muhl. and introduced U. pumila L. (Ulmaceae) in southeastern Nebraska. Phytoneuron. 10 July 2013. 2013-44. 1–23. 25 October 2017. 2153-733X.
  2. Schlautman, B., Zalapa, J., & Brunet, J. (2012). Genotypic and phenotypic characterization of Ulmus pumila (Siberian elm), Ulmus rubra (Red elm) and their hybrids. Proc. Nebraska Acad. Sci. 2012. 106 - 107.
  3. Book: Swink. Floyd. Wilhelm. Gerould. Plants of the Chicago Region. 1994. Indiana Academy of Sciences. Indianapolis. 761. 9781883362010. 4. 25 October 2017.
  4. http://vplants.org/portal/taxa/index.php?taxon=104408 "Herbarium specimen 0030674MOR "
  5. Kaul, R. B. (1995). Natural and fertile hybrids of the native red elm, Ulmus rubra, with the introduced Siberian elm, U. pumila, are now producing hybrid swarms in Nebraska. Proc. Nebraska Acad. Sci. 105: 28 - 29.
  6. Collins, P. E. (1967). Hybridization studies in the genus Ulmus. Ph.D dissertation, Univ. of Minnesota, Minneapolis.
  7. http://quercus.mortonarb.org/details_living_coll.php?id=287-47 Unnamed Ulmus × intermedia, quercus.mortonarb.org
  8. https://acorn.mortonarb.org/Detail/collections/10972 Photographs of Ulmus × intermedia, Morton Arboretum, 'Ulmus Series', acorn.mortonarb.org
  9. http://vplants.org/portal/taxa/index.php?taxon=104408 U. × notha, Morton Arboretum, vplants.org
  10. https://www.ulmen-handbuch.de/handbuch/ulmus/u_hamburg.html U. pumila x U. rubra 'Hamburg', in Handbuch der Ulmengewächse, www.ulmen-handbuch.de