I need help identifying this plant. It's a wild plant (weed) growing here at my Zone 5 Arizona house. It just began blooming this week. It has very small pink/lavender flowers, borne in clusters, which open in the morning and close at night. It's leaves are serrated and arranged in a rosette. As you can see in the pictures below, each flower is about 1 centimeter across, the leaves are about 5 centimeters long, and the whole plant is about 7 inches across.

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Thanks in advance for your help.