Antonius Josephus Adrianus Uitewaal (1899-1963) was born in Utrecht, Netherlands. He worked a reproduction photographer. After becoming interested in succulents, he was disappointed by the handbooks obtained, and began translating the works of Hawortha and Salm-Dyck. Under the same interest of Haworthia, he also became a close friend of Karl von Poellnitz. Uitewaal was described as the greatest European student of Haworthia.
Uitewaal’s greatest contribution to Haworthia was his observation that a natural subdivision of the genus could be made based on floral characteristics. He noted that the flowers could be divided into those which were triangular in cross-section (section Triangulares) and those which were hexagonal (section Hexangulares). Using other characteristics such as peduncle thickness, he further subdivided the latter into two subsections, Robustipedunculatae and Gracilipedunculatae. His division inspired Bayer to establish 3 Haworthia subgenera.