Trichomes

Trichomes are plant hairs composed of one or more cells.  Almost all gesneriads have leaves and flowers with trichomes.  These hairs serve multiple purposes, including discouraging insect predators, reflecting sunlight, and insulating the plant body.  The trichomes of the nettle (Urtica dioica), for instance, contain a substance which irritates the skin of a person who touches the leaf and breaks any trichomes.

This cool picture, courtesy of Miriam Denham, shows the trichomes on Sinningia sulcata, magnified many times.  The trichomes appear to be four (sometimes three) cells long.  The purpose of these trichomes is probably insulation, but some species, such as S. amambayensis, have hairs with sticky wax-like substance(s) to deter insects.