I know very little about the family Gesneriaceae and pretty much all that I do know comes from a presentation I delivered at the Robert Brown 200 conference held at the Royal Botanic Gardens in Sydney, in 2002. I say delivered because that's exactly what I did: no more no less. World expert from Austria, Anton Weber, prepared the talk and eventually turned it into a paper for the journal Telopea, but was unable to make it to Australia.
Rhytidophyllum doesn't rate a mention in that paper, and nor should it. It's not represented in Australia and Robert Brown, as far as I know, knew nothing of it. All species grow on islands of the Caribbean or in the north of South America. The species I saw today was described from a plant collected in Cuba in the 1860s and seems to be limited to that country.
Ron Myhr dismisses the species on his Gesneriad site with a single sentence 'This large plant produces interesting inflorescences with greenish flowers, without a great deal of decorative value'. His photograph is from Kew Gardens, the same plant as mine. It's worth adding that Robert Hall did win best in show in 2002 with a young specimen of this species, also photographed by Ron Myhr on the same site.
Still Myhr is probably right. Rhytidophyllum exsertum is perhaps best described as interesting rather than decorative. On Sunday though, in the tropical section of the Princess of Wales Conservatory and protected from the chilly and wet London day, this plant was charming. At least close up
Most of its flowers were finished but you can see here one on the left with its female bit (the stigma on top of the style) ready and male bits (stamens) tucked away, and other with male bits sticking out and spent. (The flowers pictured at top are also like the one on the right - at what is called post-anthesis - and you can't even see the stigma.)
Although yellowish flowers with red markings is typically associated with bat pollination, most species of Rhytidophyllum, including this one, seem to be pollinated by a mix of flying animals - bats, hummingbirds and bees. It may be these species are in evolutionary transition. In addition to their batty flower colour, they produce nectar and release pollen at night, when hummingbirds and bees are in short supply. So interesting, even if not decorative.