When today's email, with photos, came in, I decided I had better make a few images of the offending plant of my own. So I waltzed on out the door of my office building and into this slightly weedy flowerbed twenty feet away.
This species is a winter annual, and those little rosettes of leaves are often evident from late fall on through the winter. This growth habit enables the plants to pop forth early in the spring, and burst into flower and fruit with vigor before most other plants have reached the reproductive stage.
Hairy bittercress has been around ever since I began botanical field work around 1990. But it surely has become much more abundant since then. The first Franklin County, Ohio collection dates to 1898, but back then it would have been a seldom-seen oddity. By 1991, the mustard had been collected in at least 29 Ohio counties, but definitely was scarcer than today, and I'm confident that it is easily found now in all 88 of our counties. No one collected this plant in Michigan until 1976, but I'm sure it isn't hard to find up there now.
Why is hairy bittercress becoming so prolific? In a word, nurseries. Many of the first collections in the "wild" come from greenhouses and nurseries, where hairy bittercress would pop up as a weed. Such a growing environment sets the stage for an eventual massive escape. The tiny, prolific seeds easily adhere to feet, digging implements, and anything else they come into contact with. Thus, the soil that nursery stock is planted and transported in eventually becomes infested with hairy bittercress seed.
As localized infestations become more severe, the plants are more easily spread, not only in the local yardscape but also to new sites. Before long a giant mustardish snowball is rolling downhill and out of control, casting seeds far and wide. And now, we are at the point where there is such a proliferation of hairy bittercress that nearly everyone notices the plants.
Fortunately, because of their diminutive stature and propensity for growing in open, already highly disturbed environments, Cardamine hirsuta does not cause much harm to most natural areas. That's not to say that it can't; infestation of a habitat SUCH AS THIS could be very bad for some of our highly specialized native mustards.
I'm afraid hairy bittercress will be the bane of many a gardener for some time to come.