Ambrosia (Ragweed)

 
 
Ambrosia is commonly known as Ragweed.  The name ragweed has been given due to the raggedy shape of its leaves.  About 21 species of ragweed occur in North America.  Ragweeds are annual or perennial herbs with lobed or divided leaves, which are deeply bipinnately dissected, lower ones opposite, upper ones alternate.  It is the most important plant of pollinosis in the USA and follows a general pattern of pollination from the north to the south, with a few exceptions.
 
Pollen Morphology:
 
Grain, echinate, tricolporate, with short colpi.  The sexine is thick and contains short spines with pointed apices and broad bases, some times with intermixed spinules.
 
Flowering and Pollen Aerobiology:
 
Thought most temperate North America composites flower during midsummer or late summer to autumn.  In Florida and the southwest flowering may be much earlier or late or may be round the year for few species.  Pollens are characteristic of wind-pollinated.
 
Allergenicity:
 
Most important cause of pollinosis in North America.