Solving a Mystery...Kind of

Walking near the South Sycamore Wetlands recently I came across a plant I hadn't noticed before on the Greenway. It was off the main paths, in a clump of shrubby trees down near one of the ponds. After all the goldenrod and thistle, this plant's tall spike of whorled flowers was downright exotic.

Whorls of flowers

Unfortunately in the winter there isn't always much available to identify a plant. The flowers have long since dried up and lost their color, petals and leaves having dropped off. The stem was obviously square-shaped, which made me think "mint family." I took a few photos and went home to see what I could find.

 

First stop: the books. Many are organized based on flower color, which was no help in this particular case. Instead I paged through quickly, looking for a flower that matched the general appearance of my stranger. American Bugleweed? Has a square stem and whorled flowers and is "common in wet, marshy areas," but the description says they are "tiny"; my whorls seemed about the size of a quarter. Field Mint (Mentha arvensis) seems very close, but I don't feel good about a positive ID with so little to go on.

 

Off to Google! Image search: square stem whorled flowers iowa. Result: a lot of colorful flowers that look nothing like my stranger. Take off "iowa" replace with "winter." And scroll through hundreds of photos. Wait--what was that? Pennyroyal? The image of a winter inflorescence looks exactly right, but on further review pennyroyal is much smaller, only about a foot tall. Not to mention its distribution map shows a big empty space between populations on both coasts. Definitely not pennyroyal.

The square stem

 

When books and Google fail, I always turn to one of the many online forums full of fellow plant enthusiasts. How lucky are we to have a worldwide population ready and willing to help answer our questions? I post my photo with general details (description, where it was found) and wait a few hours. The first response was...looks like pennyroyal, but much too big. Well, it was good to have that confirmed. The next response suggested Motherwort (Leonurus cardiaca), an invasive found throughout much of the continental U.S.

 

So now I've got two possibilities:Field Mint, a native, and Motherwort, invasive. My somewhat depressing rule of thumb is to go with the invasive when given a choice, simply because the areas I frequent tend to be those disturbed places where non-native plants tend to thrive. Add on the size difference--Motherwort being closer to the 2'-3' height of my mystery plant, compared to 1' or so for the Field Mint--and I feel pretty comfortable calling it Motherwort. I will make a note to return to the area next summer to confirm, when presumably it will be in full bloom with leaves and flowers to make a positive ID.