Ask-a-Dave's-Gardener: Unidentified plant Perennial Purple Day Blooming Flowers, 4 by scubasid

scubasid wrote:
I got this plant 3 years ago a perennial its in South Carolina , Each morning it sprouts brand new PURPLE FLOWERS ( Silver Dollar in Size ) and at dusk it drops them , now in Sept it was 55 over night and the flowers didn\'t bloom all the way open, DOES ANY ONE KNOW THE TYPE and NAME of this Plant ? In winter I cut back the stalks to 3 inches above ground and cover them up with mulch and in spring it sprouts out shoots that becomes stems into this Plant now about 5ft tall. Help Please.