Single-leaf streptocarpus, like S. haygarthii, often grow on vertical surfaces with the leaf hanging straight down. The unifoliate form is particularly well-adapted to such a position, as a taller plant with leaves sticking out would tend to pull out of the very shallow medium (mainly moss) within which the plant is rooted. Colonies can efficiently cover almost the entire surface of such a rock or tree. A photo of flowers of the species can be seen here. A closer view of some of these plants can be seen here.
Monophyllaea species, in Asia, can have a very similar form and habitat.
A different flower pattern can be seen here. This clone has different markings than those seen on the plant above.