My nan used to have these purple shamrocks in her spare room and I've just found out their official name - Oxalis (specifically - Oxalis regnellii atropurpurea - la la la whatever...)
I love them. Are they a leaf or a flower? I'm not sure.
They close up at night as if they're sleeping and stretch out in the morning. They also have little pink flowers that pop out but my nan used to chop these off a she was convinced it would make the plant bushier. I don't know if it's true.