Where found, osage-orange pollen has been reported to cause cross-reactions with pollen of the paper mulberry (Morus spp.), and is therefore potentially a serious cause of pollinosis.
Osage-orange or hedge-apple is a dioecious (separate-sexed) tree that can reach 50 feet in height and 2 feet in diameter. Shiny, 3- to 5-inch, dark green leaves are attached to thorny branches with thorns 1 inch long. This plant produces a milky sap that is a dermal, or skin, allergen. Maclura grows in the southcentral U.S. and prairie regions of the Mississippi River basin. Female trees produce large, inedible fruits about 3 to 5 inches in diameter which ripen in autumn and are believed by some to repel cockroaches and spiders. The leaves and fruits are reported to be poisonous. Male trees have distinct flowers that are small, dull green-yellow balls on short stalks (bottle brush appearance). Wood from the Osage-orange tree has been used, in the past, to make fence posts and archery bows.
Pollen grains of Maclura are spheroidal and 2-4 porate. The pores are usually circular and sometimes slightly aspidate and the margin is distinctly annulate. The opercula is centrally thickened and protruding. The sexine is tectate and usually scabrate, the surface appearing rough and thin. The intine is thin except below the pores and is characterized by an oncus.
Grains of Maclura are 21-25 micometers in diameter.
The shaded areas on the map indicates where the genus has been observed in the United States.
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