From FCBS .... "There are several groups within Tillandsia and some may be raised to generic status.
One of these groups contains the very small Tillandsias and are called Diaphoranthema, with the world authority being Dr Walter Till.
Dr. Till does most of his publishing in the German Journal 'Die Bromelie'. His main paper on Diaphoranthema is in Selbyana 13; 88-94 1992.
The 1st group proposed in Diaphoranthema is the CALIGINOSA Group.
This group includes T. caliginosa, cotagaitensis, porongoensis, and tenebra."