Aztec Sweet Herb and Stevia

This spring I purchased from Richters a plug tray of Aztec Sweet herb and love it. Recently I've heard of "Stevia (S. rebaudiana) and wonder if this is the same plant?

No, stevia is quite different. Stevia is the source of non-caloric natural sweeteners. Originally from Paraguay in South America, it became popular in Japan in the early part of the 20th century and is now becoming popular elsewhere. The sweetener substances in stevia are steviosides, said to be hundreds of times sweeter than sugar. In the native form, stevia also contains bitter substances which have been partly removed by breeding less bitter strains and by developing extraction methods that selectively eliminate the bitter components.
The sweetener in Aztec sweet herb, hernandulcin, is similarly sweet and non-caloric. But the leaves contain appreciable amounts of camphor which is off-putting and medicinal in taste for many people. On account of the camphor it is probably not wise to rely on Aztec sweet herb as an everyday sweetener – occasional use is probably okay – but that is a matter of personal preference. Small amounts of camphor in the diet may be a good thing – helping to unclog arteries, etc. – but there are some health risks if too much is ingested over time. The Canadian health department, for example, has limited the use of camphor in consumer products over concerns about camphor's effects.