Years ago a friend gave me a clump of Oxalis (wood sorrel) with pink blossoms to put in my garden. Years later it continues to spread and pops up everywhere in early spring and then again in the fall. I now have oxalis in 4 different varieties including shamrocks.
The purple variety, Oxalis triangularis is my favorite. The leaves move in response to light levels, opening in high ambient light (in the day) and closing at low light levels (at night).
Here is the variety Oxalis Iron Star. It produces clusters of rosy pink blossoms in the summer. Deep purple markings highlight the junction of the four heart-shaped leaves for dramatic additions to pots, window boxes and sunny windowsills. I planted these from bulbs 2 weeks ago and now they are ready for a shady spot in the front garden.