Number of Genera
The number of genera is between 150 and 160, and is thus much higher than usually given in textbooks and horticultural pages. For two reasons, no precise number can be given at present: (1) There is still some discussion about the delimitation of genera; for instance, the Australian genus Lenbrassia is sometimes kept separate, sometimes included in Fieldia; the two species of Depanthus should be possibly returned to Coronanthera; it has been suggested to split the huge genus Columnea into 5 genera, but there is no general agreement on this; new revisions almost always end up in establishing new genera, reviving old genera, or combining genera. (2) For a number of genera it is not clear whether they should be included in Gesneriaceae at all, e.g. Cubitanthus, Jerdonia, Sanango and others.
Number of Species
Estimation of species number is still more difficult than the indication of the number of genera. The numbers given in some textbooks, and in particular by H. Wiehler (1983) (“over 3700”), seem to be a bit generous. Recently, J. K. Boggan from the Smithsonian Institution, Washington, has scrupulously summed-up all species accepted in 2004, and presented a number of 3220 species (see World Checklist of Gesneriaceae, below). This is, however, just a snap-shot. With every new revision the number will change, as old names are sunk into synonymy and new names are established. Much of this uncertainty is due to a few poorly known large genera, e.g., Besleria, Aeschynanthus, and especially Cyrtandra.
Additional References on Genera and Species