Encyclopedia of Mormonism, pg. 553; “Among the Latter-day Saints it is the accepted practice to hail Christ as Lord, King, and Messiah, and to shout hosannas to his holy name, on all days and at all times. But it is not the common practice to single out Palm Sunday for any special commemorative worship. Rather the Latter-day Saints memorialize the transcendent events of their era, such things as the coming of John the Baptist, the restoration of the Melchizedek Priesthood, the conferral of the sealing keys by Elijah, and the organization of the Church again on earth.”
Matthew 10:32-33; “Whosoever therefore shall confess me before men, him will I confess also before my Father which is in heaven. 33 But whosoever shall deny me before men, him will I also deny before my Father which is in heaven.”
I don’t know of a Christian church in the world that doesn’t observe Palm Sunday.