In the eastern portion of Oklahoma, the dominant native trees are primarily oak (Quercus), hickory (Carya), and pine (Pinus) similar to the vegetation of Arkansas and southern Missouri. Of the 26 oak species reported for Oklahoma, 21 are found in or right outside this zone. Identifying the pollen as oak is sufficient when testing for allergens because cross-reactivity is prevalent with pollen in this genus.
The hickory species of significance in hay fever is Carya illinoinensis, or pecan. It is found along streams and in moist bottomlands; also, it is widely cultivated in pure stands. Pecan trees begin their brief reproductive period later than most of the other spring trees.
Some literature suggests that Ulmus americana (American elm) is of moderate importance today. Due to Dutch elm disease, in many areas of the United States nearly 80% of American elms have died. In Oklahoma, however, American elms are still a major hay fever problem and the pollen is abundant. Although the American elm produces pollen in late winter and early spring, other Ulmus species release pollen in summer and early fall.
In Oklahoma, 11 species of grasses are considered major allergens, all occurring in Zone 1. Some were introduced and have become established with the native flora, while others are cultivated in lawns and prairies. The most important grasses in this area are Cynodon dactylon (bermuda grass) and Festuca pratensis (meadow fescue). Artemisia ludoviciana (white sagebrush), Amaranthus spp. (pigweeds), and Ambrosia spp. (ragweeds) are weeds associated with the numerous disturbed habitats, the edges of forests, and clearings.