Ontario Weeds: Common ragweed
Excerpt from Publication 505, Ontario Weeds,
Order this publication
Table of Contents
Name: Common ragweed, Ambrosia artemisiifolia
Stems & Roots: Stems erect, 15-150cm
(6-60in.) high, usually much-branched, hairless or hairy throughout;
lower leaves opposite (2 per node) but becoming alternate (1 per
node) higher on the plant, bright green to slightly yellowish-green
on young plants, becoming grayish-green on older plants, compound
and finely divided, the final divisions usually coarsely toothed.
Similar Species: It is distinguished by its finely divided leaves, which are opposite in the lower part and alternate in the upper part of the plant, these being yellow-green at first, later gray-green with age, and its very numerous, tiny, non-showy, greenish male flower heads clustered along slender branches in the upper part of the plant.
It is essential that Goldenrod, Solidago spp., [verge d'or, solidage], not be confused with Common ragweed. Several species of Goldenrod occur throughout Ontario in meadows, pastures, woodland, river flats and roadsides, and have very conspicuous bright yellow inflorescences during the ragweed hayfever season of late summer and autumn. Goldenrods do produce pollen but only in small quantities, and their pollen is heavy and sticky. It is not carried on the wind and the plants are pollinated by insects. Because Goldenrod pollen is not carried on the wind, it must not be blamed as the source of irritation for ragweed hay fever sufferers.
Caution: Common ragweed is the most important cause of hay fever during August and September. Although inconspicuous and not recognized by most people, the tiny male flower beads hanging on their slender stalks produce huge quantities of very light pollen. As the pollen falls from these hanging flowers, it is caught by the wind and may be carried for distances greater than 200 km (125 miles). Hay fever sufferers, therefore, may be affected by pollen from ragweed plants far away.
For more information:
Toll Free: 1-877-424-1300