Most Streptocarpus species are small soft-leaved herbs growing in protected environments such as forests or deep gorges, but they also grow in microhabitats in deep rock cracks that give protection against the sun and the elements. In biogeographical terms, they often occur in the so-called Afromontane regions on the high African and Madagascan mountains where in places it can get very cold. This means that many Streptocarpus are more cold tolerant in their cultivation than many of the tropical Geseneriaceae.
Streptocarpus are unique in many ways. Seedling development shows an unequal development of the two cotyledons after germination. This is discussed by Anton Weber in his article on the family Gesneriaceae where he comments on the genus Streptocarpus with specific reference to “exceptional morphologies”: https://gesneriads.info/articles/gesneriaceae/exceptional-morphologies-i/ He describes the development of the cotyledons after germination, specifically the formation of unifoliate plants in which one cotyledon stops growing and the other cotyledon, referred to as a macrocotyledon, develops to form the single leaf or phyllomorph of the adult plant. In the plurifoliate, rosulate Streptocarpus their cotyledon development is similar, but they then develop a succession of phyllomorphs which are not a perfectly symmetrical rosette of leaves but rather irregular and somewhat asymmetrical.
In caulescent Streptocarpus, after the development of the macrocotyledon, a stem develops from which opposite leaves sprout. In the case of Saintpaulia this stem has no internodes, and the plant grows a succession of opposite leaves to give a perfectly symmetrical leaf rosette. In caulescent species their stems are mainly soft, but some are even hard and woody shrubs.
Streptocarpus also has some species with oddball morphologies, such as Streptocarpus decipiens. This miniature species from South Africa, which grows in deep, protected rock cracks, has a frail stem growing from a basal leaf, making it caulescent, but the plant consists of a basal phyllomorph as in the unifoliate and rosulate species from which a tender stem grows with one to three tiny opposite leaves branching off the stem. Its name is derived from this morphology because it is deceptive. DNA work shows that it does belong in subgenus Streptocarpus. Other oddballs have creeping rhizome stem morphologies, such as in Streptocarpus bullatus and related species.
Although Streptocarpus frequently grow in moist environments, some species have adapted to drought through leaf abscission, and complete desiccation i.e. resurrection plant type mechanisms as described in https://gesneriads.info/articles/gesneriaceae/habitats-special-adaptations/ as in Streptocarpus exsertus (Bytebier, personal communication). Streptocarpus shows almost all of the morphological variation seen across the whole family Gesneriaceae, which complicates their classification.