African violets are a HUGE industry in
North America. Many thousands of varieties are available, selected for novel
flower colour but also for improved
flowering time, disease resistance and other
economically important traits.
One of the interesting things about African violet production is that they are propagated entirely through tissue culture. The old-fashioned method involved taking horizontally-sliced leaf explants ("cuttings") and planting them in soil until new plantlets grew along the cut edge. More recently, sterile in vitro methods have been developed, improving control over the culture process and excluding pests and diseases in the early phases of growing. These propagation methods have the advantage that they produce many genetically identical plants, allowing mass cultivation and sale of varieties that do not "breed true".