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Five decades of daily pollen measurements have catalogued a growing number of imported and native plants in Tucson, Arizona, a city that has a high prevalence of allergic rhinitis and asthma. These plants have contributed a large proportion of the overall pollen rain and include mulberry, olive, juniper, cypress, privet, mesquite, Bermuda grass, ragweed, Palmer’s amaranth, and Russian thistle. Factors contributing to these increases in pollen include population growth as well as changing architectural and landscape preferences. The institution of pollen control laws, inner city development, and nonreplacement of allergenic trees along with the growing popularity of desert landscaping suggests that trend reversal may be occurring.