Rex begonias are in the rhizomatous group and typically grow horizontally (creeping rhizomes) although some may grow more upright but have shortened stems. Rexes (King Begonia) usually have colorful leaves compared to other rhizomatous begonias. The lines become blurred as more hybrids have been introduced as to what is a rex and what looks like a rex. The true rex species (B. rex Putzey) is one of the parents of rex hybrids but a lot of rex looking begonias have no rex Putzey in them. Rexes typically bloom in fall but can have sporadic blooming at other times. Rexes usually defoliate in winter too and go into a dormancy for a few weeks. Rexes are also very susceptible to powdery mildew.