I recently posted the following photo as a plant quiz...
Some of the guesses included Boehmeria cylindrica, Urtica dioica (or maybe Laportea canadensis), and Pilea pumila. None of these were correct, but what do they all have in common? They are all in the family Urticaceae. When I first saw this plant, I was convinced it was in the family Urticaceae, but nothing fit. As I was about to give up until I could see a more mature specimen, I thought... man, those leaves look like mulberry. Then it hit me that there was an herbaceous, non-native mulberry that I had never seen. I looked up Fatoua villosa, Mulberry Weed, and sure enough, it was a perfect fit. Interestingly, this species was once known as Urtica villosa.
This is Fatoua villosa, Mulberry Weed, or Hairy Crabweed (Moraceae). It was introduced in the United States from east Asia as recently as the 1960s. First found in Louisiana, it has rapidly spread throughout the southeastern United States, pushing north into Indiana and Ohio; it has also been recorded in California and Washington. Much of its spread has been attributed to the horticultural trade, where it persists as a weed in greenhouses.
In many of the northern locations for this plant, it has been found more commonly inside greenhouses. Only very recently (1991 in Ohio) has this species been observed outside of greenhouses in the northern extent of its range.
Mulberry weed is an annual that continuously produces an abundance of seeds from the time it is a very small plant until it reaches a maximum height of up to 80 cm. When mature, the seeds are "explosively expelled," according to Flora of North America.
Watch for this weed around greenhouses, in waste areas, and in disturbed sites as it continues its northward expansion.
Congratulations, Justin and Susan, for correctly identifying the plant in this plant quiz.