S. dunnii is the source of all of the red color in hybrid Streptocarpus. Its single leaf is particularly distinctive due to its grayish-green tone. The flowers on this plant can be seen in closeup here and here. Note the “abscission zone”, the portion of the leaf that has died off. The ability to jettison a portion of the leaf allows the plant to survive dry seasons by reducing the amount of surface area subject to transpiration of water.
A photo of a show plant illustrates the variation within the species.