Ulmus × intermedia

Short description: Elm cultivar

Ulmus × intermedia

Hybrid parentage| 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]

## Contents

* 1 Description
* 2 Pests and diseases
* 3 Cultivation
* 4 Cultivars
* 5 References

## 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).[7]

## 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.[8][9][7]

## Cultivars

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

## References

1. ↑ 1.0 1.1 1.2 Elowsky, C.G.; Jordon-Thaden, I.E.; Kaul, R.B. (10 July 2013). "A morphological analysis of a hybrid swarm of native Ulmus rubra Muhl. and introduced U. pumila L. (Ulmaceae) in southeastern Nebraska". Phytoneuron 2013-44: 1–23. ISSN 2153-733X. http://www.phytoneuron.net/2013Phytoneuron/44PhytoN-Elmhybrid.pdf. Retrieved 25 October 2017.
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. ↑ Swink, Floyd; Wilhelm, Gerould (1994). Plants of the Chicago Region (4 ed.). Indianapolis: Indiana Academy of Sciences. p. 761. ISBN 9781883362010. https://books.google.com/books?id=xfZGAQAAIAAJ&q=notha. Retrieved 25 October 2017.
4. ↑ "Herbarium specimen 0030674MOR ". Morton Arboretum Herbarium. Sheet labelled U. × notha Wilhelm & Ware, Chicago region (1993); "Herbarium specimen - L.4405627". Botany catalogues. Naturalis Biodiversity Center. http://data.biodiversitydata.nl/naturalis/specimen/L.4405627. Ulmus pumila x Ulmus rubra, Richland Center, Wisconsin; Missouri Botanical Garden leaves specimen (2015); "Herbarium specimen - L.4405626". Botany catalogues. Naturalis Biodiversity Center. http://data.biodiversitydata.nl/naturalis/specimen/L.4405626. Ulmus pumila x Ulmus rubra, Richland Center, Wisconsin; Missouri Botanical Garden flowers specimen (2015)
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. ↑ 7.0 7.1 U. × notha, Morton Arboretum , vplants.org
8. ↑ Unnamed Ulmus × intermedia, quercus.mortonarb.org
9. ↑ Photographs of Ulmus × intermedia, Morton Arboretum, 'Ulmus Series', acorn.mortonarb.org
10. ↑ U. pumila x U. rubra 'Hamburg', in Handbuch der Ulmengewächse, www.ulmen-handbuch.de

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