In his original description of the first species of Streptocarpus to be discovered, by Hooker in 1827, described as Didymocarpus rexii (see historical overview of the genus section), he describes that he was charmed by the species. This obvious horticultural attraction of the neat rosette of leaves and ready flowering habit of Streptocarpus rexii rapidly led to an increase in its popularity as a house plant.
This was well before the first Saintpaulia species were brought into cultivation (around 1890) and was therefore a stimulus to bring more Streptocarpus species into cultivation. Clarke reported there were 17 by 1883 (Clarke, 1883). This included unifoliates such as Streptocarpus polyanthus which had been collected some 50 km inland from the coastal town of Durban on the South African East Coast. S. polyanthus ssp. polyanthus produces beautiful keyhole shaped flowers which are presented forward with flat faces and this attracted hybridizers to try to establish this flower shape on a rosulate plant through crossing it with Streptocarpus rexii. Both French and English hybridizers produced interesting hybrids in the period from about 1850.
Major progress was made after the introduction of the red-flowered Streptocarpus dunnii to Kew in 1886. Hybrids were made with S. rexii and S. parviflorus and these were incorporated into a hybridization program with S. polyanthus, S. saundersii, S. wendlandii, in which the horticulturist Veitch was involved. For a detailed report on this hybridization program see Hilliard and Burtt (1971) pages 96 to 101.
By crossing the large cultivar Streptocarpus ‘Merton Blue’ with Streptocarpus johannis, the hybrid S. ‘Constant Nymph’ was developed in 1946. This hybrid formed the base for many modern hybrids.
Another notable event was the development of the deep purple flowered Streptocarpus hybrids by the John Innes Institute. These were the result of mutations induced by radiation.
In recent times the development of double-flowered Streptocarpus hybrids has caused quite a stir and are now readily available. Certain species have again been crossed into the modern hybrids to address specific characteristics. Streptocarpus kentaniensis seems less day-length sensitive than other species, and flowers in natural light indoors in winter even in very short-day regions like the United Kingdom. It has been used to extend the flowering period of hybrids. Streptocarpus lilliputana, which has Acanth-type bowed tube-shaped flowers is very small and has been introduced into hybridization programs to produce smaller hybrids with attractive bow-shaped flowers. Although this species does not possess variegated leaves it somehow transmits this to its progeny (Dale Martens, personal communication).
Caulescent Streptocarpus have also been hybridized with one notable cross between S. stomandrus and S. saxorum. This cross has been made twice and is therefore known under the names ‘Concord Blue’ and ‘Good Hope’. It has proven very popular, with plants available for sale in many conventional garden centers during the spring season, as well as from specialist growers year-round. It is most often seen as S. ‘Concord Blue’.
One of the problems of cultivating rosulate Streptocarpus is their large size. Future hybridization trends will probably focus more on breeding smaller varieties that occupy less space and in terms of the horticultural trade, need less space for transportation. Streptocarpus leaves tend to be brittle and leaf breakage during the transport of large plants is a problem, so developing more flexibly-leaved plants may be a priority.
What has not been exploited in horticulture are the small unifoliates. Many are tiny and conform to the smaller size restrictions. If they could be hybridized to generate smaller unifoliates with attractive colours then this could be a new horticultural avenue for Streptocarpus, although the monocarpic nature of most unifoliates may be a barrier.