Allergen of the MonthdJapanese Maple There are about 125 species and multiple cultivars of maples that are woody trees or shrubs of north temperate climates. Two thirds of Acer species are found in eastern Asia.1,2 There are 13 native North American species, with ten of these found in Canada, and with others introduced as ornamentals.2,3 Japanese maple, Acer palmatum, is native to Japan, China and Korea, and commonly cultivated throughout the United States.3e5 Climate change with increasing dormancy temperatures has been shown to augment wound healing in A palmatum.6 Leaf extracts from Acer species show antimicrobial activity, especially against grampositive bacteria.7 An aqueous extract from A tegmentosum shows antiangiogenic activity, suggesting potential use as an anticancer agent.8 A palmatum is a small tree up to 6e10 m in height with a spreading crown. Bark is light gray and fissured. Leaves have 7e9 lobes, double-toothed, separated by deep narrow V-shaped notches, some cultivars with almost fern-like appearance.4,5 Leaves are pale green turning to red-purple in the autumn. Flowers are red, 6e8 mm, in branched erect clusters appearing with the leaves in April.3,4 Many maples are amphiphilous, in addition to insect pollination, dispersing sufficient airborne pollen to induce hayfever.9e11 Acer pollen sensitization has been found in 32.8% of a group of New York City allergy patients.12 Rises in asthma admissions, clinic visits, and over-the-counter medication use have been correlated with increases in Acer as well as other tree pollen counts.13e15 Based on morphology and rbcL chloroplast gene sequencing, the two genera of Acer and Dipteronia, are within the samaroid clade in the family Sapindaceae.1 These genera had been previous classified as the separate family Aceraceae. Cross-reactivity data on most Acer species is scanty and not consistent. Prausnitz-Küstner neutralization data had shown cross-inhibition between maple and order Fagales members, but RAST inhibition using box elder solid phase showed poor inhibition with most trees tested, and none with hazel, birch or alder.16,17 Additionally, there is poor skin test correlation between box elder, A negundo, and red maple, A rubrum.18 Preliminary data suggests there may be some crossreactivity of Platanus Pla a 1 allergen with Acer.19 Acer grains are tricolpate, slightly prolate, 33x32 mm. Furrows are long and tapering, stretching from pole to pole, with a smooth membrane. Sexine is 0.8 mm thick, with distinct striate surface texturing. Striae tend to run parallel with the furrows, and are comprised of coarse granules arranged in rows. Nexine is 0.6 mm thick with prominent bacula, and intine is 0.8e1.0 mm thick.11,20 Text & Photography Ó Richard W. Weber, M.D. References [1] Judd WS, Campbell CS, Kellogg EA, Stevens PF. Plant Systematics: A Phylogenetic Approach. Sunderland, MA: Sinauer Associates; 1999:333e342. [2] Farrar JL. Trees of the Northern United States and Canada. Ames, IA: Iowa State University Press; 1995:132e155. [3] Sibley DA. The Sibley Guide to Trees. New York: Alfred A Knopf; 2009: 332e351. [4] Phillips R. Trees of North America and Europe. New York: Random House; 1978:65e79. [5] Hora B. Oxford Encyclopedia of Trees of the World. Oxford: Equinox Ltd; 1980:231e234.

[6] Copini P, den Ouden J, Decuyper M, et al. Early wound reactions of Japanese maple during winter dormancy: the effect of two contrasting temperature regimes. AoB Plants. 2014;6:plu059. [7] Wu D, Wu XD, You XF, Ma XF, Tian WX. Inhibitory effects on bacterial growth and beta-ketoacyl-ACP reductase by different species of maple leaf extracts and tannic acid. Phytother Res. 2010;24(Suppl 1):S35eS41. [8] Kim E-C, Kim SH, Piao S-J, et al. Antiangiogenic activity of Acer tegmentosum maxim water extract in vitro and in vivo. J Korean Med Sci. 2015;30: 979e987. [9] Wodehouse RP. Hayfever Plants. New York: Hafner Publishing Co; 1971: 136e141. [10] Lewis WH, Vinay P, Zenger VE. Airborne and Allergenic Pollen of North America. Baltimore: Johns Hopkins University Press; 1983:12e15,182. [11] Wodehouse RP. Pollen Grains. New York: McGraw-Hill; 1935:438e442. [12] Lin RY, Clauss AE, Bennett ES. Hypersensitivity to common tree pollens in New York City patients. Allergy Asthma Proc. 2002;23:253e258. [13] Dales RW, Cakmak S, Judek S, Coates F. Tree pollen and hospitalization for asthma in urban Canada. Int Arch Allergy Immunol. 2008;146:241e247. [14] Zhong W, Levin L, Reponen T, et al. Analysis of short-term influences of ambient aeroallergens on pediatric asthma hospital visits. Sci Total Environ. 2006;370:330e336. [15] Ito K, Weinberger KR, Robinson GS, et al. The associations between daily spring pollen counts, over-the-counter allergy medication sales, and asthma syndrome emergency department visits in New York City, 20022012. Environ Health. 2015;14:71e82. [16] Rackemann FM, Wagner HC. The desensitization skin sites passively sensitized with serum of patients with hay fever. Crossed reactions of different pollens. The variations in the recipient. J Allergy. 1936;7:319e332. [17] Bernstein IL, Perera M, Gallagher J, et al. In vitro cross-allergenicity of major aeroallergenic pollens by the radioallergosorbent technique. J Allergy Clin Immunol. 1976;57:141e152. [18] Weber RW. Cross-reactivity of plant and animal allergens. Clin Rev Allergy Immunol. 2001;21:153e202. [19] Fernández-González D, González-Parrado Z, Vega-Maray AM, et al. Platanus pollen allergen, Pla a 1: quantification in the atmosphere and influence on a sensitizing population. Clin Exp Allergy. 2010;40:1701e1708. [20] Erdtman G. Introduction to Pollen Analysis. Waltham, MA: Chronica Botanica Co; 1954:66e67.

Reprints: Richard W. Weber, M.D. Department of Medicine National Jewish Health 1400 Jackson Street, Room J326 Denver, CO 80206.