Excerpts from Jim Conrad's
from the June 8, 2014 Newsletter issued from the Frio Canyon Nature Education
Center in the valley of the Dry Frio River in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau, USA
A small, sprawling weed showing up along streets and other very disturbed areasin Uvalde is shown above. With such clover-like, trifoliate leaves -- leaves divided into three leaflets -- you can guess that this is a member of the Bean Family, which it is. Below, a close-up shows that the tiny, hardly opening flowers display the general Bean Family "papilionaceous" shape:
This is one of several species of the genus Medicago, commonly known as medicks, though the very important forage plant Alfalfa also is a Medicago, M. asiatica. Medicago species are generally recognized as small, weedy herbs looking more or less what's in the pictures. The species we're looking at is distinguished from other Medicago species by the hairiness of its leaves and stems and, most importantly, the spiky appearance of its fruit, seen at the lower, left in the last photo. Fruits of most species are smooth, shaped like flattened cloth coin-purses, or sometimes coiled like snail shells.
Its hairiness and spiky fruits distinguish this little herb as MEDICAGO MINIMA, known variously as Bur Medick, Little Burclover, Little Medick, Small Medick, Woolly Bur Medick, and by other names. All medick species are invasive in North America, originally coming from Eurasia, especially the Mediterranean region.
Despite the Bur Medick being a genuine invasive weed, it's worth tipping the hat to. That's because it forms a symbiotic relationship with the bacterium Sinorhizobium meliloti, which can fix nitrogen, thus basically fertilizing the soil, helping other plant species eventually root themselves and prosper. I think of Bur Medick as a classic first responder. People destroy soil structure and nutrient content, and Bur Medick comes in generously offering everyone life-supporting nitrogen.