In 1948,
Aimee Camus produced a comprehensive treatment of the two major genera in the family, given the specimens available to her at the Natural History Museum in Paris. Because of the many collections available from the French colonies in subtropical and tropical Indochina, she worked extensively with stone oaks from the region. Most importantly, she provided the only existing infrageneric structure within the genus but unfortunately, many of the species from the Malesian region, south of the Isthmus of Kra, are not incorporated into this system. Her classification system included 13 subgenera, including the subgenus
Pasania which is by far the largest division within the genus. About 100 Asian species were treated separately in
Pasania, at the genus level, and occasionally the old name persists on some herbarium sheets that have not been annotated. Several of the other subgenera possess fewer than ten species and have distinctive morphologies. Few of the Malesian species are treated in Camus' system and Soepadmo, who wrote the Flora Malesiana treatment, made no attempt to update or integrate these species into Camus' system, therefore a lot of work obviously remains to be done. Camus' system was highly detailed, as three levels of organization are recognized below the subgenus, but the classification is not systematic at the lowest level. List of subgenera (No. of species in Camus' treatment):
Castanicarpus (1);
Corylopasania (2);
Cryptostylis (1);
Cyclobalanus (58);
Cyrtobalanus (1);
Eulithocarpus (11);
Gymnobalanus (10);
Liebmannia (3);
Oerstedia (1);
Pachybalanus (14);
Pasania (209);
Pseudosynaedrys (9);
Synaedrys (15); indeterminate (12). Early researchers into the family often suggested that the stone oaks were primitive in the family. An exhaustive study of the inflorescence and fruits of 73 species from eight of Camus' subgenera found that important development and evolutionary characters distinguish the major groups in the genus and indicate differences among the genera of the family. ==Species==