Hay fever occurs when susceptible individuals inhale airborne pollen released from the anthers of wind-pollinated vascular plants. The dispersal of the pollen is haphazard, not being directed by the actions of insects or other pollination vectors. To ensure that some of this pollen arrives on the stigmas of flowers of the same species, flowers of wind-pollinated species must produce very large amounts of pollen. It is these wind-pollinated species, that release very large amounts of pollen into the air, that are the major causes of hay fever. Wind-pollinated flowers, not requiring insects or other vectors for effective pollination, tend to be very small and lack special attractants. This is in contrast to plants that have flowers that are mainly or exclusively pollinated by insects or other vectors. This type of plant typically produces fairly small amounts of sticky pollen, has large flowers or flower targets with colors and markings in wavelenghth clearly visible to the potential pollination vectors, and has attractants or rewards of special interest to the pollination vectors. Common ragweed (Ambrosia artemisiifolia L.), a common weed along the margins of roadsides and in other disturbed habitats, and the major cause of hay fever in many areas is a typical wind-pollinated plant. It has very inconspicuous flowers that produce very large amounts of airborne pollen. Unfortunately, since the flowering period of common ragweed usually coincides with that of Canada goldenrod (Solidago canadensis L.), a plant with heavy sticky pollen and very showy yellow flowers that often forms a solid stand in adjacent fields, Canada goldenrod is frequently wrongly considered to be the plant causing the hay fever symptoms. The following list of hay fever plants is adapted from the publication I. John Bassett, C. W. Crompton, and J. A. Parmelee, An atlas of airborne pollen grains and common fungus spores of Canada, Research Branch, Canada Department of Agriculture, Ottawa, Monograph No. 18, 1978, 321 pages. Dr. Parmelee also has an excellent section on fungus spores that cause hay fever in this publication.

alders - Alnus species
ashes - Fraxinus species
aspens - Populus species
atriplexes - Atriplex species
basswoods - Tilia species
bayberry - Myrica pensylvanica Loisel.
beeches - Fagus species
birches - Betula species
butternuts - Juglans species
cattails - Typha species
cedars - Thuja species
chestnuts - Castanea species
cockleburs - Xanthium species
docks - Rumex species
elms - Ulmus species
grasses - family Gramineae (Poaceae)
greasewood - Sarcobatus vermiculatus (Hook.) Torr.
hemlocks - Tsuga species
hickorys - Carya species
junipers - Juniperis species
kochia - Kochia scoparia (L.) Schrad.
lamb's-quarters - Chenopodium album L.
maples - Acer species
mugwort - Artemisia vulgaris L.
nettle, stinging - Urtica dioica L.
nettle, wood - Laportea canadensis (L.) Gaudin
oaks - Quercus species
pines - Pinus species
pigweed, redroot - Amaranthus retroflexus L.
pigweed, Russian - Axiris amaranthoides L.
pigweed, tumble - Amaranthus albus L.
plantains - Plantago species
poverty weed - Iva axillaris Pursh
ragweed, common - Ambrosia artemiisifolia L.
ragweed, false - Iva xanthifolia Nutt.
ragweed, giant - Ambrosia trifida L.
ragweed, perennial - Ambrosia psilostachya DC.
sagebrushes - Artemisia species
sages - Artemisia species
sedges - Carex species
sorrels - Rumex species
sweet-fern - Comptonia peregrina (L.) Coult.
sweet gale - Myrica gale L.
sycamores - Plantanus species
thistle, Russian - Salsola kali L.
walnuts - Juglans species
willows - Salix species
wormwood, biennial - Artemisia biennis Willd.

 

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