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Code: t1
Latin name: Acer negundo
Source material: Pollen
Family: Aceraceae
Common names: Box elder, Maple ash, Ash maple, Ashleaf maple, Manitoba maple, Box elder maple, Western box elder, Black ash, California boxelder, Cutleaf maple, Cut-leaved maple, Negundo maple, Red river maple, Stinking ash, Sugar ash, Three-leaved maple

Not to be confused with the Elder t205 (Sambucus nigra) or the Grey alder t2 (Alnus incana).

Closely related species:
A. saccharum - Sugar maple
A. pseudoplatanus - Sycamore maple

Allergen Exposure

Maples, genus Acer, are abundant trees or shrubs of northern, temperate climates. Common members include box elder (A. negundo), sugar maple (or silver maple) (A. saccharum), and sycamore maple (A. pseudoplatanus). (1)

Acer (maple) is a genus of trees and shrubs, variously classified in a family of their own, the Aceraceae, or (together with the Hippocastanaceae) included in the family Sapindaceae. There are approximately 125 species, most of which are native to Asia, but several occur also in Europe, northern Africa, and North America. The species A. rubrum, red maple, appears on the Canadian flag. (1, 2)

Box elder is native to eastern and midwestern North America. It has the broadest range of the North American maples, and is found throughout eastern and central North America. (2)

The box elder is a small- to medium-sized tree, reaching heights of 10 to 15 m (up to 30 m in gardens), with a trunk diameter up to 1.2 m. It is usually fast-growing and fairly short-lived. It often has several trunks and can form impenetrable thickets. (3) The trunk is relatively short and tapering, and the crown is spreading and bushy.

The bark is thin and pale grey to light brown when young, but on maturity becomes greyish-brown, scaly, and deeply grooved or deeply cleft into broad ridges. The shoots or twigs are bright green, often with a whitish (or pink or violet), shiny, waxy coating when young. The twigs usually have white lenticels. Unlike most other maples (which usually have palmate leaves), this tree has pinnate leaves up to 10 cm long, with 3 to 7 (usually 3) elliptic to oval leaflets each. Some maples have trifoliate leaves, but only the box elder tree regularly displays more than 3 leaflets. (3) The leaflets are 3 to 7 cm long, all with irregularly toothed margins. Each leaflet is shallowly and irregularly lobed or notched, translucent light green in colour, smooth on the upper surface and paler on the underside, and in autumn becomes yellow-green and brown. (2, 3)

Box elder is dioecious, with male and female flowers occurring separately but on the same tree. The flowers are small and appear in early spring on drooping racemes 10 to 20 cm long. The male flowers are in small bundles, and the female ones in clusters on drooping, stalk-like structures. The flowers are greenish-yellow, without petals, and inconspicuous. (2) Box elder flowers in the early spring, just before the leaves appear.

The most distinctive characteristic of the maples is the fruit (seed), which comes in pairs (paired samaras) commonly known as ‘keys’, each with a thin membranous wing. The fruits are borne in pairs of drooping, 15 cm-long, pendulous clusters. The individual fruit consists of a wing with a single seed at the base, is 2.5 to 4 cm long, and is reddish brown to yellowish. In the northern hemisphere it ripens between August and October and stays on the tree through winter.

The box elder thrives in sunlight and in rich, moist soils, and is often found in lowland sites near water. Box elder wood is used for low-quality furniture, paper pulp, interior finishing, and barrel-making. Syrup can be made from the sap. (2)

Allergen Description

To date no allergens have been characterised, although potential allergenic proteins have been shown. (4)

A study investigating the effects of SO2 and NO2 on the protein content, allergenicity, and germination rate of box elder pollen reported that in urban areas, concentrations of these two substances below the limits established for human protection can indirectly aggravate pollen allergy on predisposed individuals and affect plant reproduction. (5)

Potential Cross-Reactivity

Extensive cross-reactivity among the different individual species of the genus could be expected. (6) When researchers compared levels of IgE antibodies to A. negundo and A.platanoides (Norway maple) in individuals sensitive to the allergens of these, 88% of the patients showed a very high level of cross-sensitisation. (7)

Clinical Experience

IgE mediated reactions

Box elder pollen will result in asthma, hayfever and allergic conjunctivitis in susceptible individuals. (5, 8)

In a population in Missouri, USA, skin-tested with pollen from 12 wind-pollinated tree species, box elder, willow and hickory elicited the most intense allergic reactions; and oak, birch, sycamore, black walnut and poplar, more moderate reactions; allergens from cottonwood, maple, elm and white ash were even less reactive. The authors stated that since box elder is ubiquitous and produces a strongly positive reaction among adults in this region, it should be included among skin tests of those patients known to be allergic to early spring pollen. (5)

In a study that evaluated the impact of different trees on asthma, and 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 increase in daily tree pollen concentration, percentage increases in daily hospitalisation for asthma were 2.6% for Ulmus (elm), 2.45% for the group containing Pinaceae (pine, fir, spruce), Tsuga (hemlock) and Larix (larch, tamarack); 2.3% for the group containing Quercus (oak) and Castanea (chestnut); and 2.2% for Acer (box elder and maple). (9)

In a study in Morgantown, West Virginia, USA, the purpose of which was to identify the frequency of positive skin tests to outdoor allergens among younger children who had asthma, a total of 687 children with asthma were evaluated. Children between 12 and 24 months of age had a 29% incidence of pollen sensitisation. Notably, 49% of 3- and 4-year-olds were sensitised to outdoor allergens. Primary sensitising pollens in this age group were short ragweed, box elder, and June grass. (10)

In a study of 371 allergy patients tested serologically for hypersensitivity to prevalent tree pollens in the area surrounding New York, the highest prevalence of hypersensitivity was for oak (34.3%), birch (32.9%), and box elder (32.8%) tree pollens. (11)

Acer pollen has been recorded in aerobiological studies in south-eastern Spain (12) and in Porto in Portugal, (13) and has been reported to be a prominent pollen in Philadelphia, Pennsylvania, and suburban Cherry Hill, New Jersey, US. (14)

Sensitisation rates in a general population group of elementary school to teenage students in Incheon, Jeju, and Ulsan in Korea were investigated. Skin-prick tests were performed on 5 094 students. Elementary school students were tested for 18 common aeroallergens, whereas middle and high school students were tested for 25 allergens. The 25 allergens included Dermatophagoides pteronyssinus, Dermatophagoides farinae, pollen (birch, alder, oak, Japanese cedar, pine, willow, elm, maple, Bermuda grass, timothy grass, rye grass, orchard grass, meadow grass, vernal grass, mugwort, Japanese hop, fat hen, ragweed, and plantain), and mould (Penicillium, Aspergillus, Cladosporium, and Alternaria). The sensitisation rates in descending order were 25.8% (D. pteronyssinus), 18.7% (D. farinae), 6.2% (mugwort), and 4.1% (willow) in Incheon; 33.4% (D. pteronyssinus), 24.8% (D. farinae), 15.4% (Japanese cedar), and 7.3% (Alternaria) in Jeju; and 32.8% (D. pteronyssinus), 30.3% (D. farinae), 10.1% (alder), and 8.7% (birch) in Ulsan. The dust mite allergen showed the highest sensitisation rate of the 3 regions. The sensitisation rate of tree pollen was the highest in Ulsan, whereas that of Alternaria was the highest in Jeju. The ragweed sensitisation rates were 0.99% in Incheon, 1.1% in Jeju, and 0.8% in Ulsan. For Acer (maple –­ species not specified), sensitisation ranged from 1.1 to 2.2. (15)

Non-commercial immunotherapy has been attempted. (16, 17)

Other reactions

The pollen of Acer negundo and another species of maple have been implicated as a cause of airborne contact dermatitis. Positive patch-test reactions to ‘box elder pollen oil’ and to ‘maple pollen oil’ were described in two patients. Two cases were reported, and observations of a third case in which the symptoms occurred coincided with the tree pollination period. These patients had typical lesions of plant dermatitis on the exposed areas of their skin. (18)

Compiled by Dr Harris Steinman, 


  1. Weber RW. Maples, genus Acer. Ann Allergy Asthma Immunol 2002;88(2):A-4.
  2. Wikipedia contributors, ‘Maple’, Wikipedia, The Free Encyclopedia, Accessed 15 January 2013.
  3. Wikipedia contributors, ‘Acer negundo’, Wikipedia, The Free Encyclopedia, Accessed 15 January 2013.
  4. Ribeiro H, Oliveira M, Ribeiro N, Cruz A, Ferreira A, Machado H, Reis A, Abreu I. Pollen allergenic potential nature of some trees species: a multidisciplinary approach using aerobiological, immunochemical and hospital admissions data. Environ Res 2009;109(3):328-33.
  5. Sousa R, Duque L, Duarte AJ, Gomes CR, Ribeiro H, Cruz A, Esteves da Silva JC, Abreu I. In vitro exposure of Acer negundo pollen to atmospheric levels of SO₂ and NO₂: effects on allergenicity and germination. Environ Sci Technol 2012;46(4):2406-12.
  6. Yman L. Botanical relations and immunological cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09.
  7. Pharmacia AB Allergy. Which allergens? Pharmacia AB publication. Uppsala. Sweden. 1985: ISBN 91-970475-5-4.
  8. Lewis WH, Imber WE. Allergy epidemiology in the St. Louis, Missouri, area. III. Trees. Ann Allergy 1975;35(2):113-9.
  9. Dales RE, Cakmak S, Judek S, Coates F. Tree pollen and hospitalization for asthma in urban Canada. Int Arch Allergy Immunol 2008;146(3):241-7.
  10. Ogershok PR, Warner DJ, Hogan MB, Wilson NW. Prevalence of pollen sensitization in younger children who have asthma. Allergy Asthma Proc 2007;28(6):654-8.
  11. Lin RY, Clauss AE, Bennett ES. Hypersensitivity to common tree pollens in New York City patients. Allergy Asthma Proc 2002;23(4):253-8.
  12. Munuera Giner M, Garcia Selles J. Allergenic pollens in south-east Spain. Allergy 2002;57(1):59-60.
  13. Ribeiro H, Oliveira M, Abreu I. Intradiurnal variation of allergenic pollen in the city of Porto (Portugal). Aerobiologia 2008;24(3):173-7.
  14. Dvorin DJ, Lee JJ, Belecanech GA, Goldstein MF, Dunsky EH. A comparative, volumetric survey of airborne pollen in Philadelphia, Pennsylvania (1991-1997) and Cherry Hill, New Jersey (1995-1997). Ann Allergy Asthma Immunol 2001;87(5):394-404.
  15. Park SH, Lim DH, Son BK, Kim JH, Song YE, Oh IB, Kim YH, Lee KH, Kim SY, Hong SC. Sensitization rates of airborne pollen and mold in children. Korean J Pediatr 2012;55(9):322-9.
  16. Öztürk S, Çalıskaner AZ, Güleç M, Erel F, Kartal Ö, Karaayvaz M, Kutlu A. Effects of allergen specific immunotherapy on the allergens excluded from the treatment. Eur J Gen Med 2008;5(4):232-8.
  17. Grier TJ. How's my dosing? A one-step, math-free guide for comparing your clinic's maintenance immunotherapy doses to current practice parameter recommendations. Ann Allergy Asthma Immunol 2012;108(3):201-5.
  18. Lovell RG, Mathews KP and Sheldon JM. Dermatitis venenata from tree pollen oils; a clinical report. J Allergy 1955;26(5):408-14.

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.