Flower of the Day: Giant Ragweed

Ambrosia trifida; Asteraceae (aster family)


After posting about goldenrods over the last few days, I have to take this opportunity to dispel a common myth: goldenrod pollen is not an allergen.  The culprit at this time of year is ragweed.  Goldenrod takes the blame because it’s so showy, but ragweed, with its tiny little unassuming flowers, is doing the damage.

Actually the flowers are quite interesting.  They are completely without petals or sepals.  Each of the yellow dots in the picture above is an individual flower.

There are three species of ragweed found in this area.  The one pictured here can grow to 12 feet tall, and is found in every state of the union except Nevada. Here’s a leaf, which can get to a foot long:


The other species are annual ragweed (A. artemisiifolia, with three subspecies, one alien and two native), and Cuman or perennial ragweed (A. psilostachya). The former is found everywhere; the latter everywhere except Delaware, Maryland, Virginia, West Virginia, and Kentucky.

All of these ragweeds are listed as weedy and/or invasive by multiple authorities.

Remember: don’t blame the goldenrods for your misery.

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