Delta Journal
by Bob Thomas

You know that a plant must have some interesting qualities if it only grows in disturbed areas. Such is the case with ragweed, a plant that connotes a drippy nose and runny eyes for many.

A wry sense of humor led to ragweed being given the generic name Ambrosia, meaning “food of the gods.” Its rough surfaced leaves are regularly eaten only by insects, though horses and cows will consume them if other food is scarce.

Two species abound in south Louisiana. Giant ragweed (Ambrosia trifida) may be l0 feet tall with large deeply lobed leaves. Common, or dwarf, ragweed (A. artemisifolia) is shorter, usually four feet tall, and has delicately dissected leaves. The flowers of both are in the junction between leaves and stems while the pollen is produced in upside-down cup-like structures lining the branches. Ragweed pollen is distributed by the wind and is a primary cause of allergies during the fall.

Ragweed is truly a pioneer species, normally being one of the first to invade barren soils. It is a very important element in our ecosystem in that it produces nutrients that further enrich its soil, thus paving the way for the invasion of other species having different ecological requirements. This phenomenon is known as plant succession.

Another curious characteristic accelerates the eventual disappearance of ragweed. As they grow, some roots die as new ones develop. These decaying roots release a toxin that is harmful only to ragweed. When concentrations are high enough, the soil can no longer support these invaders and they die, thus paving the way for new species of plants to replace them.

So, if you are allergic to ragweed pollen, have patience. This, too, shall pass!

Also published in Nature Profile, The Times Picayune, October 3, 1989.