Fields covered with large swaths of lavender-tinted flowers are a common sight in rural Missouri this time of year. Pretty weeds, that's all they are. Just henbit. You probably have a few here and there in your yard. They're not particularly noticible in small numbers.
Henbit (Lamium amplexicaule) is a winter annual that grows from 4 to 12 inches tall. It's one of those weeds that serves a useful purpose in my opinion. It covers the ground in the winter and holds the soil in place, but it's not that difficult to eradicate in the spring when it's time for something else to grow there. It spreads only by seeds, likes moist areas, and seems to thrive in sun or shade. It's one of the earliest plants to green up in the spring, and thus drew the attention of our Jersey cow, who appreciates a tasty snack on the way back to the barn in the evening.