List of elm cultivars, hybrids and hybrid cultivars

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The starting-points for List of elm cultivars, hybrids and hybrid cultivars were threefold: (1) Green's 'Registration of Cultivar Names in Ulmus ' (1964),^[1] based on the contemporary nomenclature of elm species and wild hybrids; (2) Krüssmann's confirmation or correction of cultivar-names in his monumental Handbuch der Laubgehölze (1976);^[2] and (3) Santamour and Bentz's 'Updated Checklist of Elm (Ulmus) Cultivars for use in North America' (1995).^[3] Since the 1990s there have been many new cultivars, some 'disease-resistant', either species cultivars (e.g. U. minor 'Ademuz', U. americana 'New Harmony') or cultivars with complex hybrid origins, the subject of ongoing trials. Information on these is taken from post-1990 scientific papers (see 'Further reading' below), pteleologists' articles,^[4][5][6][7] and updated handbooks.^[8] There has not yet (2024) been a single recent collation comparable to Green's.

Green and Krüssmann acknowledged their debt to Rehder's list of elm-cultivar synonyms (1949),^[9] and to Schneider (1906),^[10] but the digitisation of older dendrologies, handbooks, and nursery-catalogues^[11][12][13] added cultivars and cultivation information missed or omitted by these four authorities.^{[note 1]} The list below makes good some of these omissions, additions justified by the survival of extensive elm collections in disease-control locations such as Edinburgh (known to have been stocked from one such nursery^[14]), Brighton, Sweden,^[7] and New Zealand. Australia remains disease-free (2024) and has in quantity both well-known clones (e.g. 'Lutescens') and at least one old cultivar missed by Green and Krüssmann ('Canadian Giant'), as well as others that do not match European 'types'.^[15] "Deliberate planting of selected clones," wrote Spencer (1995) "combined with chance hybridisation, has resulted in a mix of elms [in Australia] rather different from that in England"^[16] (see Elms in Australia).

The older elm cultivars (sometimes called 'varieties') usually bore simple descriptive Latin names (e.g. 'Tortuosa', 'Argenteo-Variegata', 'Stricta') under their contemporary species headings, or, later, under hybrid headings, as hybrids were then understood. Early lists, with no more information than this,^[17] abound, and are a further source for the articles listed below; one of the fullest is, e.g., Beissner's (1903).^[18] Amongst the more discursive treatments, however, that included cultivation-history and subjective comment (and sometimes illustrations), used in articles in this list, were those of Loudon (1838)^[19] and Elwes and Henry (1913) in the UK,^[20] Browne in USA (1851),^[21] Petzold in Germany (1864),^[22] and Fontaine in the Nertherlands (1965).^[23] These more discursive and subjective dendrologists are frequently cited in the articles listed below for information that would have been out of place in Green and Krüssmann.

The turn of the 20th century was the heyday of ornamental elm cultivation,^{[note 2][20][24]} and Green noted that many cultivars had been inadequately described or illustrated before they were almost wiped out by the catastrophes of two Dutch elm disease epidemics and two world wars. Some had been described only from juvenile specimens whose ultimate size was unknown (e.g. U. minor 'Umbraculifera Gracilis' Späth). The digitisation of university and arboretum herbarium specimens, however, (leaves and fruit), bearing original labels, – a process more advanced, by the 2020s, in European^[25] and American collections^[26] than in those of the UK,^[27][28] – and of old photographs of known cultivar-locations (see e.g. 'Atropurpurea'), has confirmed or supplemented the descriptions in many of the listed items. 'Lost' cultivars identified by Royal Botanic Garden Edinburgh since 2016 through such old planting-location information,^[14] and through herbarium specimens, – and returned to cultivation, – include U. × hollandica 'Wentworthii Pendula', U. minor 'Umbraculifera Gracilis' Späth, and U. glabra 'Concavaefolia'.^[29][30][31]

Until the early 20th century, both wych cultivars and those of large-leaved European hybrids were often classified as Ulmus montana.^[11][20][18] The likely hybrid origin of some of the latter had, however, long been suspected,^[10] English carpenters for example referring to their 'Dutch elm' as 'bastard elm',^[20] while nurserymen knew that popular cultivars like 'Belgica' and 'Vegeta' could be raised reliably only by vegetative propagation or cloning, their seedlings not coming true to type.^[20] The nomenclature of hybrids was systematised by the mid-20th century.^[9] Research leading to the selection and breeding of cultivars resistant to Dutch elm disease was under way in the Netherlands from the 1920s, in the US from the 1930s, in Italy from the 1970s, and in Spain from the 1990s.^[32]

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