Photo by Andreas Rockstein licensed under CC BY-SA 2.0

Common ragweed (Ambrosia artemisiifolia), the bane of hay fever sufferers. This could quite possibly be one of the most despised plants whether people realize it or not. It is ragweed, not goldenrod, that is responsible for causing hay fever. All this is thanks to the copious amounts of pollen it wafts into the breeze. With all that being said, I could not call this In Defense of Plants if I did not come to the defense of ragweed.

Despite all the suffering it causes, ragweeds are enormously important plants ecologically. We already know they produce a lot of pollen, but that pollen is doing more than just making you stuffy and fertilizing other ragweeds. It is also feeding bees. Because it flowers so late into the season, ragweed offers up a prodigious source of protein-rich pollen for bees gearing up for fall and winter. Even before they flower, ragweed is a valuable food source for the caterpillars of many butterflies and moths including species like the wavy-lined emerald and various bird dropping moths. It's not just insects either. The seeds of ragweed are rich in fatty oils. Birds and small mammals readily consume ragweed seeds to help fatten up for the lean months to come.

Ragweed also offers us some cultural significance too. Before European settlement, ragweed is believed to have had a much narrower distribution. Palynologists use pollen taken from lake and bog sediment cores to track ancient climates and plant communities. Because ragweed produces so much pollen, it is a useful species to look for when studying core sediments. As pollen falls out of the air and settles on lakes or bogs, it eventually sinks to the bottom where it can remain buried in a rather pristine state for millennia. Palynologists have actually been able to use ragweed pollen as a way of tracking the settlement history of North America. As colonies advanced further and further, they opened up huge chunks of land, inadvertently creating ample opportunities for ragweed to expand its range. As such, ragweed pollen taken from lake cores has proven to be a pretty precise clue for studying our own history.

For as much as we despise it, ragweed thrives on the kind of disturbance that we humans are so good at creating. We are the ones to blame for our own suffering when it comes to hay fever, not the plants.