Echinacea is an herb that is familiar and popular. In Native American herbalism, it is used for certain infectious diseases (colds, influenza), and for treating cancer. Echinacea is rich in alklyamides that trigger the CB2 receptor.
In western herbology, Echinacea is used for colds and flu, and it is seen as a 'immune booster.' The research on the 'boosting' ability of echinacea is quite mixed, and an alternative hypothesis is that echinacea shaves a day or two off of the tail end of a cold or flu through potent anti-inflammatory mechanisms, which appear to be mediated by the CB2 receptor.
Echinacea may not be the best plant to grow to get a medicine for pressing the CB2 button. Echinacea takes 18 months or more to form harvestable roots. Digging and cleaning the roots requires lots of labor. And echinacea preparations vary widely; their properties are not as consistent or predictable as with other CB2 agonists. Spilanthes is more productive and probably more predictable.