You can call me biased, I fully admit it, but in my opinion, Columnea is clearly one of the most fascinatingly diverse genera of all Gesneriaceae! I will try to convince you why I think this is so.
First of all, it is the largest of all neotropical (read American tropics) Gesneriaceae genera in terms of the number of species, somewhere around 300. For a taxonomist that is in and of itself interesting, not to mention a lifetime or two of work to try and understand. However, for an ecologist or evolutionary biologist, it also poses a number of interesting questions from the basic “why are there so many species?” to the more detailed questions regarding the origin of each of the morphological traits that have emerged within the genus. For a collector of gesneriads, Columnea can seem a daunting challenge, both to try and gather so many species together and to keep them alive and thriving.
Aside from the intellectual challenge that Columnea presents, the many species in the genus are often very beautiful, with flowers and foliage that reward both casual observation and close inspection. The fact that many of the showiest species are also amenable to growing in our homes is a special added bonus.