Ragweed

Ragweed — Ragweeds (Ambrosia), also called bitterweeds and bloodweeds, are a genus of flowering plants from the sunflower family (Asteraceae).

The scientific name of this genus is sometimes claimed to be derived from the Ancient Greek term for the perfumed nourishment of the gods, ambrosia which would be ironic since the genus is best known for one fact: its pollen produces severe and widespread allergies. However, the generic name is actually cognate with the name of the divine dish, both being derived from ambrotos, “immortal”. In the case of the plants, this aptly refers to their tenaciousness, which makes it hard to rid an area of them if they occur as invasive weeds.

Ragweeds occur in temperate regions of the northern hemisphere and South America. Ragweeds prefer dry, sunny grassy plains, sandy soils, and to grow along river banks, along roadsides, disturbed soils, vacant lots and ruderal sites. Ragweed was far less common in the Eastern United States before major land clearance by European settlers began in the late 18th century.

There are c.41 species worldwide. Many are adapted to the arid climates of the desert. Burrobush (A. dumosa) is one of the most arid-adapted perennials in North America. About 10 species occur in the Sonoran Desert.

Ragweeds are annuals, perennials, and shrubs and subshrubs (called bursages), with erect, hispid stems growing in large clumps to a height of usually 75-90 cm. The stems are basally branched. They form a slender taproot or a creeping rhizome. Common Ragweed (A. artemisifolia) is the most widespread of this genus in North America. It attains a height of about a meter. Great Ragweed (Giant Ragweed, “Horseweed”; A. trifida), may grow to four meters (13 feet) or more.