Mixed blessings (goldenrods and ragweed)

Today I am enjoying our summer-like weather in early fall, lying on my hammock under a brilliant blue sky, listening to the wind blow through the trees. Yes, that same wind does periodically drop leaves from the honey locust in our backyard right into my coffee cup, and yes, the leaves on the maple tree in front of me show a good amount of orange, but I am in a tank top and shorts, and for now I will pretend it is still summer. I think this time of year is absolutely gorgeous, even more so because I know soon the mild weather will turn first wet and chilly, then dark and at times brutally cold.  It’s also the time of year when work becomes a much bigger piece of my life, as it does for anyone who teaches, sometimes overwhelmingly so.  And it’s also the time of year my seasonal allergies grow to near Godzilla-sized proportions, leaving me red-eyed, itchy-nosed, and generally feeling tired and grumpy, though I do find some entertainment in imagining my allergies as Godzilla himself, stamping through the urban landscape of my immune system, wreaking havoc on all the typically orderly processes through which my body decides what is ‘safe’ and what is ‘dangerous’…

Two plants dominate my world in late summer, goldenrod (the beautiful) and ragweed (the terrible).  Goldenrod is one of the showiest flowers to bloom all year, with bright yellow flowers that appear just at the edge of late summer and early fall. These tall narrow plants with their showy plume of flowers grow best in ‘disturbed’ habitats, which means they are found in areas we generally think of as underdeveloped or neglected.  Roadside edges, unused fields and vacant lots all turn a glorious bright yellow in late August or early September, and the color lingers usually until the first real frost of fall.  I love goldenrod, how its brilliant yellow appears against the dark green leaves of deep summer, and how that brilliance persists even as the green in those leaves is replaced by yellows, oranges, reds and browns. 

Each yellow plume of a goldenrod is actually made of many small individual flowers.  In fact, each flower looks a bit like a tiny entirely yellow daisy.  (picture)  Goldenrods are a collection of different species in the genus Solidago, which is in turn a member of the Aster family (Asteraceae), a family which includes daisies, chrysanthemums, and unfortunately, the ragweeds.  In New England alone we have over twenty different species of goldenrods each with its own particular habitat preferences (follow this link for more fun detail). 

All goldenrods are a very important resource for insects and birds that remain in the area through the fall. Its showy yellow flowers are designed to attract a variety of pollinators including bees, wasps, butterflies and other insects.  Monarch butterflies in particular are common visitors to goldenrod flowers, which are an important source of food for these insects as they begin their migration to breeding grounds in Mexico.  Many other insects feed on the pollen in the flowers or hatch from eggs and quickly burrow into plant, forming visible bumps (or ‘galls’) in the stem itself.

Birds visit goldenrod to eat the insects attracted by its flowers.  Chickadees and downy woodpeckers peck through galls in goldenrod stems to dig out the protein-rich insect larvae found inside.  In fact gall-forming insect larvae even provide food for birds that overwinter in snowy areas of the country.  As the goldenrod flowers wilt and turn brown, chickadees, goldfinches and sparrows eat the plant’s tiny seeds.

A second plant blooms almost simultaneously with goldenrod, and that is the dreaded ragweed, a group of plants also in the Aster family but in the genus Ambrosia.  One might wonder, especially the 10% of us in the U.S. with a ragweed allergy, why on earth this genus carries the name “Ambrosia” and not something like “Apaisiosia” which would mean “awful” or “abominable”.   “Ambrosia” brings to mind, depending on where you are from, either the food and drink that gave immortality to the Greek gods, or a strange ‘salad’ served in the Midwest that includes, among other things, canned pineapple, sour cream, and miniature multicolored marshmallows (don’t believe me? Google the word “ambrosia” and see what you find).  Why on earth that recipe is called a ‘salad’, I have no idea,  but I once had a similar ‘salad’ at a Thanksgiving dinner when I lived in Minneapolis which included sour cream, canned mandarin orange juice (but not the oranges), apple chunks and cut up Snickers bars.  I have to admit it was quite tasty.  But not a ‘salad’.  Sorry, I digress…

So why are plants in this genus given the name Ambrosia?  Plants of the genus are native to Central and especially North America and so were named based on preserved specimens that were sent back to European botanists to study.  Ragweeds were in fact given the name Ambrosia by perhaps the most famous botanist ever, Carl Linnaeus, in 1753 (see https://en.wikipedia.org/wiki/Species_Plantarum for more info).  Why Linnaeus chose this name for the group appears to be a mystery, but I would hazard a guess that the man did NOT suffer from a ragweed allergy, or he would have chosen an entirely different name for the group. 

Ragweed flowers are inconspicuous, being the same green color as the plant’s leaves and stem.  Like goldenrod, ragweed flowers are tiny and cluster together into long plumes at the ends of its upper stems (picture).  Unlike goldenrod, which relies on animals to pollinate it, ragweed flowers release pollen into the air, allowing wind to carry pollen from one plant to the next.  Wind is a dubious pollinator; a grain of wind-carried ragweed pollen is much less likely to reach an available ragweed flower than a grain of goldenrod pollen hitching a ride from one flower to the next on the leg of a  bumblebee. To make up for this uncertainty, ragweed flowers produces copious amounts of pollen, up to 1 billion pollen grains per plant, and those pollen grains can travel for hundreds of miles before they fall out of the air and onto hopefully (for the plant) a ragweed flower, or into (more likely) a person’s nose or eyes. 

All plants produce pollen, and any wind-pollinated plant produces large amounts of it. Why, then, is ragweed pollen such a problem for so many people?  The answer to that question may be a simple case of mistaken identity. What we consider an allergic response is most likely actually a misdirected response to the presence of a parasitic organism.  Because parasites, while small, are too big to be handled by our immune cells, our body’s response to them is to try to eject or expel them by sneezing, coughing, or washing them out with tears and mucous production (snot).  Ragweed pollen is covered with proteins, some of which apparently trigger an “it’s a worm!!!” immune response for some of us, leading to sneezing, coughing, and runny itchy eyes and noses.

Like goldenrods, ragweeds grow best in disturbed areas such as roadsides and overgrown gardens.  In fact, the range for both species has grown as a direct result of human activities.  Paleoethnobotanists, researchers who study past relationships between people and plants by identifying pollen samples in deep layers of buried soil, recognize something called “the ambrosia horizon”, which is a layer of buried soil full of ragweed pollen.  Below this layer, ragweed pollen is rare, and above this layer, ragweed pollen is common.  The ambrosia horizon corresponds directly to the timing of European colonization and expansion into North America and the conversion of undisturbed lands into agricultural fields.  Agricultural activities provided abundant disturbed habitats for quick growing, fast reproducing species like ragweeds and goldenrods, and these species experienced a population explosion in any area newly converted to agricultural fields.  Ragweeds have also jumped across the Atlantic and are now found as invasive species in Europe. Unfortunately, not only have human activities continue to provide abundant habitat for ragweeds, our impact on climate is also extending the group’s range and flowering period.  Basically, humans created the ragweed problem, and we are making it worse for ourselves with every passing year.

The beginning of fall is always a mixed blessing, with its beautiful colors and cool, crisp nights.  Apples are everywhere, and the cool temperatures just beg for baking apple crisps and pies, butternut squash soup, home made bread.  The beginning of a new school year is exciting for both me and my kids, but it also means a growing ‘to-do’ list that is increasingly difficult to keep up with, and I feel like I have less time to enjoy the last days of sun and goldenrods before the sky turns grey and the world fades into the muted reds and browns of November.  But I look forward to the first real frost, when each blade of grass and my car windows are covered with webs of sparkling water crystals, and when ragweed pollen is finally gone from the air.