||Information for patients with allergy and related
in the Southwest
Environment and allergic disease
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Allergenic Pollen in the
What makes pollen allergenic?
Most pollen will become an allergen if a susceptible
person is exposed to a sufficient quantity of it. Attractive, brightly colored
flowers that are pollinated only by insects (e.g., roses) rarely cause allergy (except in
florists). Wind-pollinated plants produce comparatively huge quantities of pollen
that become airborne easily, and can travel 20 miles or more on a windy day.
Therefore most of the pollen found in air samples is derived from plants pollinated by
wind. Pollen from all grasses, many weeds and most of the common deciduous trees are
disseminated by wind from unattractive, inconspicuous flowers.
Pollen in the Desert
Wind-pollinated plants are ubiquitous throughout the world, indicating that there really
is no safe haven for a person who is sensitive to several types of pollen.
However, differences in climate and soil composition explain the obvious differences in
the range and type of flora seen in different regions in North America. In the
arid southwest, the rarity of a hard freeze allows something to flower at any time of the
year. The Sonoran desert extends though large areas of the southwest and
has a diverse flora. Diversity of the flora has been increased further by the
introduction into urban areas of a large number of species from other regions of North
America and the world.
Regional differences in plant prevalence and flowering seasons
Bermuda grass, an introduced species now prevalent in the southwest, has allergens
that are unique among the grasses in North America. Grasses have a much longer
flowering season in the southwest than in cooler areas, and some weed species flower both
in the spring and the fall. One of the allergenic weeds in Southern Arizona,
Triangle-leaf Bursage, is a Ragweed and flowers mainly in the spring, unlike the scourge
of allergy sufferers in most other parts of the United States (Short and Tall Ragweed)
which flowers in the fall. Fortunately, airborne Ragweed pollen counts in the
southwest do not reach the enormous levels often recorded in the midwest and east.
Allergens from Bermuda grass pollen and possibly from other types of pollen are carried in
the wind as a fine particulate dust that can get into airways in the lung to provoke
Allergenic Plants in Arizona
In Arizona they include many species that are native to the region and many introduced
species. Native allergenic plants include triangle leaf bursage (a species of Ambrosia),
desert ragweed (Ambrosia dumosa), desert broom (Baccharis), Wing Scale (Atriplex
canescens), Mesquite (Prosopis) and PaloVerde (Cercidium). A
large number of introduced trees and shrubs such as Olive, White Mulberry, weeds such as
Russian Thistle (Salsola) and Australian Saltbush, and introduced grasses including
Bermuda grass (Cynodon dactylon) produce allergenic pollen. There is some
evidence that horticulture accompanying increasing urbanization has caused increasing
levels of certain types of atmospheric pollen in the past 40 years. More
recently, it is thought that climate change from global warming may be responsible for
increasing the amounts of airborne ragweed pollen, a type prevalent in most of the
continental United States. (See Tables
for details of individual plants that may cause allergy in Maricopa, Pinal and Pima
Benson L, Darrow RA: Trees and Shrubs of the Southwestern Deserts.
The University of Arizona Press, Tucson, 3rd Edition, 1981.
Kearney TH, Peebles RH et al: Arizona Flora. The University of California Press,
Berkeley, 2nd Edition, 1960.
Parker KF: An Illustrated Guide to Arizona Weeds. The University of
Arizona Press, Tucson, 1972
Turner RM, Bowers JE, Burgess TL: Sonoran Desert Plants. An Ecological
Atlas. The University of Arizona Press, Tucson, 1995.
Lewis WH, VinayP, Zenger VE: Airborne and Allergenic Pollen of North America.
The Johns Hopkins University Press, Baltimore, 1983.
For additional information, see links in Environment
and Allergic disease and links to other internet sites.
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Disclaimer: This site is for educational
purposes only. Any information that you have found in this web site is not
intended to replace medical care or advice given to you by your own physicians. You should
consider consulting your local medical library and other web sites for additional
Comments and suggestions welcome! Email: firstname.lastname@example.org
Content Owner: Michael J. Schumacher, MB, FRACP, The
University of Arizona