Ulmus americana 'St. Croix'
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The American Elm cultivar ''Ulmus americana'' 'St. Croix' is a recent (2008) selection cloned from a large tree growing on a farm near Afton, Minnesota, which has displayed a high resistance to Dutch elm disease (DED).Palmer, K. ''Star Tribune'', May 5, 2009. A U S patent, PP 20097, was granted in 2009.


Description

‘St. Croix’ has an open-grown, spreading, vase-shaped crown. The growth rate is fast and typical of the species in Minnesota. The bark is typically divided into grayish, flat-topped ridges, which are separated by roughly diamond-shaped fissures and which become indefinite in pattern in the canopy. Bark on young branches is smooth with inconspicuous lenticels. The twigs are slender, zigzag, brown, glabrous or slightly pubescent; lateral buds are about 6 mm long, ovoid, acute but not sharp-pointed, smooth or sparingly downy, chestnut-brown. Leaves are deciduous, simple, alternate, short-petioled, 2-ranked, dark green (closest to 006600 on HTML True Color Chart), 10–15 cm (4–6 inches) long, 2.5–5 cm (1–2 inches) wide and oblong-obovate to elliptical, the margin coarsely doubly serrate, the apex acuminate while the base is typically inequilateral; surfaces glabrous (smooth) or slightly scabrous (roughened) above, usually pubescent below; veins alternate, ascending, parallel and extending from central vein to apex of longest serrations. The
perfect Perfect commonly refers to: * Perfection, completeness, excellence * Perfect (grammar), a grammatical category in some languages Perfect may also refer to: Film * Perfect (1985 film), ''Perfect'' (1985 film), a romantic drama * Perfect (2018 f ...
apetalous wind-pollinated flowers are vernal, appearing before the leaves unfold, born in long-pedicelled fascicles of 3 or 4. The fruit is a
samara Samara ( rus, Сама́ра, p=sɐˈmarə), known from 1935 to 1991 as Kuybyshev (; ), is the largest city and administrative centre of Samara Oblast. The city is located at the confluence of the Volga and the Samara (Volga), Samara rivers, with ...
maturing in the spring as the leaves unfold; about 12 mm (½ inch) long, oval to oblong-obovate, deeply notched at apex, margin ciliate with smooth surfaces.Bliska, C., Bliska, P., Stennes, M., & Giblin, C. (2008). American elm tree named 'St. Croix'
''Patent Application US 20080196132 P1''
/ref> The parent tree at Afton had a
d.b.h. Diameter at breast height, or DBH, is a standard method of expressing the diameter of the trunk or bole of a standing tree. DBH is one of the most common dendrometric measurements. Tree trunks are measured at the height of an adult's breast, ...
of 1.9 m when measured in 2008.


Pests and diseases

Resistance to Dutch elm disease has been confirmed by inoculation trials conducted at Minnesota State University. Tested alongside established cultivars 'Valley Forge', 'Miller Park', and wild specimens, all three cultivars became symptomatic but survived, whereas the wild trees died. However, the relative percentages of defoliation and dieback of the three cultivars have not been disclosed. The species as a whole is susceptible to
Elm Yellows Elm yellows is a plant disease of elm trees that is spread by leafhoppers or by root grafts."Elm Yellows." Elmcare.Com. 19 Mar. 2008 . Elm yellows, also known as elm phloem necrosis, is very aggressive, with no known cure. Elm yellows occurs in the ...
; it is also moderately preferred for feeding and reproduction by the adult Elm Leaf Beetle '' Xanthogaleruca luteola'', and highly preferred for feeding by the Japanese Beetle ''
Popillia japonica The Japanese beetle (''Popillia japonica'') is a species of scarab beetle. The adult measures in length and in width, has iridescent copper-colored elytra and a green thorax and head. It is not very destructive in Japan (where it is control ...
'' in the United States. ''U. americana'' is also the most susceptible of all the elms to
verticillium wilt Verticillium wilt is a wilt disease affecting over 350 species of eudicot plants. It is caused by six species of ''Verticillium'' fungi: ''V. dahliae'', ''V. albo-atrum'', ''V. longisporum'', ''V. nubilum'', ''V. theobromae'' and ''V. tricorpu ...
.


Cultivation

The tree is propagated and marketed by Bailey Nurserie

of Newport, Minnesota, Newport, Minnesota.


Etymology

The tree is named for the St. Croix river valley.


Accessions


North America

* Morton Arboretum, Illinois, US. Acc. no. 125-2014


References

{{Elm species, varieties, hybrids, hybrid cultivars and species cultivars , state=collapsed American elm cultivar Ulmus articles missing images Ulmus