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Carolina foxtail | The wild thing for the week of 1/12/09
There are 21 species of ragweed in North America, but two cause allergy sufferers the most problems: Common ragweed, Ambrosia artemisiifolia, and giant ragweed, Ambrosia trifida.
Common ragweed is considered a noxious weed in Ontario, but it hasn't made that list in Missouri. However, one plant can produce more than 1 billion pollen grains, and the wind can carry the light pollen up to 125 miles.
A North American native and member of the Aster family, common ragweed seedlings start out with spatula-shaped cotyledons in April or May. The first true leaves are opposite and form lobes. On older plants, leaves are opposite until the fourth node and are deeply cut and hairy. Higher leaves are alternate. The summer annual can grow up to 5 feet tall. A ragweed plant has both male and female flower heads. Only male flowers produce pollen. The plants flower from August through September.