t45 Cedar elm

See also: Elm (White elm or American elm, Ulmus americana) t8

Other Topics

The elm family, Ulmaceae, contains 6 genera, the most important being Ulmus, Planera, and Zelkova. (Hackberries [Celtis spp.] used to be included in the Elm family but are more closely related to Urticaceae, and have been placed in a separate family, Celtidaceae. (1) There are about 45 species of elm worldwide, found within the temperate Northern Hemisphere, with about 4 introduced species in the USA, and six native to the North American continent east of the Rocky Mountains. There are 25 species of Ulmus. (1, 2, 3)

In the 1930s, Dutch elm disease devastated white elm trees in North America, as well as in Europe. The disease, a fungal blight, was caused by the Ascomycete Ophiostoma ulmi, and transmitted through the native elm bark beetle Hylurgopinus rufipes. (4) All elms are susceptible to the fungus to some degree, in particular American elm (U. americana) and September elm (U. serotina). Chinese elm (U. parvifolia), Siberian elm (U. pumila) and red or slippery elm (U. rubra) are highly or modestly resistant. (1, 3)

Cedar elm is a deciduous tree native to south-central North America. It grows mainly in southern and eastern Texas, eastern Oklahoma, Arkansas and Louisiana, with small populations in western Mississippi, south-western Tennessee and north-western Florida. (5, 6,) It also occurs in north-eastern Mexico. It is the most prevalent elm in Texas. Typically, it grows well in flat river bottom areas referred to as cedar elm flats.

The cedar elm is a medium-sized to large tree, growing to 24-27 m tall, with a rounded crown. The trunk is about 75 cm in diameter. Twigs have corky wings. The leaves are small (2.5 - 5 cm long and 1.3 - 2 cm broad) and elliptical, with serrated edges, asymmetric leaf take-off on either side of the leaf stem, and a leathery, sandpapery upper surface. Cedar elm has the smallest leaves of all native North American elms.

Elm flowers are produced in the late summer or early autumn. They are greenish, small and inconspicuous, with a reddish-purple colour and short stalks at the leaf base. All elms are wind-pollinated and are prolific pollen producers. Pollination is intense over a short period of time. Individual trees may release their pollen load over a 2- to 3-day period. Cedar elm pollinates from July to October. (1) The fruit is a small winged samara 8 to 10 mm long, maturing quickly in late autumn, after the flowering.

Elms are also grown for shade and ornament. Commercially, they are used in a variety of industries for their heavy, exceedingly hard wood.

IgE-mediated reactions

Intense hay fever, but not asthma, has been described. (6, 7) Although only very few reports document sensitisation to pollen from this tree, anecdotal evidence from areas where the tree is commonly found suggests that allergic sensitisation is common following exposure to the pollen. Furthermore, because of the close family relationship with white elm tree, which induces asthma, allergic rhinitis and allergic conjunctivitis, (8,9) clinical inferences may be drawn. (See White elm t8.)

In a Canadian study that evaluated the impact of different trees on asthma, along with the association between daily hospitalisations for asthma and daily concentrations of different tree pollens in 10 large Canadian cities, it was reported that for an interquartile increase in daily tree pollen concentration, the percentage increase in daily hospitalisation for asthma was 2.63% for Ulmus. (10)

Aerobiology studies often do not draw distinctions between the various species of Ulmus, but this may not be problematic; considering the close relationship between species of elm, cross-sensitisation or cross-reactivity to Ulmus is possible, and hence inferences can be drawn, including that individuals sensitised to cedar elm may be affected in areas where white elm or other members of the genus produce pollen.

In Tampa, Florida, in the USA, where the major tree-pollen season occurs from December until May, with a minor season occurring from October to November, elm tree pollen is important during the minor season. (11)

In Cordoba, Spain, aerobiology studies have reported pollen grains from the closely related species Ulmus minor in the air. (12) In Siena, in central Italy, elm tree pollen was found to be an important aeroallergen in March, but not during the rest of the tree-pollen season, (13) whereas in Modena, in northern Italy, the elm family contributed little pollen to the air (about 1% of the total recorded). (9)

In aerobiology studies of 9 districts of northern China, the most common aeroallergens in spring were often Ulmus, Populus and Salix. (1) Elm has also been reported to be an important tree pollen in Tehran, Iran. (15)

Pollen concentrations in the atmosphere of Lublin (eastern Poland) were reported to be the highest for Betula, Pinaceae and Alnus; and the lowest for Ulmus, Fagus and Corylus. Significantly, total pollen grains for Ulmus varied almost twofold between successive years. (16) Pollen from the Ulmus species has been reported to be an important allergen in Zagreb, Poland. (17)

No allergens have been characterised.

Cross Reactivity

Extensive cross-reactivity between the different individual species of the genus could be expected, as well as to a certain degree among members of the family Ulmaceae. (18) However, to date this has not been documented.

In a Spanish study, individuals with melon allergy were found to have a higher prevalence of asthma and an increased frequency of sensitisation to several tree and weed pollens, predominantly Ulmus and Ambrosia. (19)

Last reviewed: May 2022