ornamentally less powerful?

So I've heard that the ornamental St. John's Wort, the big-leaved rampant stuff, just doesn't pack the same punch as the small weedy St. John's Wort. Does anyone have info on how big the difference is?

(Like if someone's in a pinch is it even worth it to try to harvest a 'watered-down' ornamental cousin?)

And what are some other examples of this? Medicinal plants being breeded out of their medicinal habit...

I have read reports of similiar problems with artemesia. The good stuff is showing promise in modern medicine. http://www.cancerplants.com/herb_news/artemisia_annua.html

On a completely non-scientific basis, I've often heard that plants selected for their ornamental value are often less potent medicinally than the species. I would assume if you found a selection that had been bred for higher content of the medicinally active components this would not be true.

I'm not having a lot of luck finding scientific backup for this on the web. However, I've heard medicinal plant folks say it specifically of Echinacea and some of the other common edibles.

Also, with regard to St. John's Wort, keep in mind that in the nursery trade I think pretty much everything within the Genus Hypericum is called St. John's Wort. I believe the medicinal species is Hypericum perforatum. I believe the rampant ground cover is Hypericum calycinum, which has no known medicinal uses according to pfaf.org.

Before harvesting any medicinal plant I would look it up in at least two good sources. For starters you could look at Richo Cech's "Making Plant Medicine" and Michael Moore's "Medicinal Plants of the Pacific West" (or one of his books for other regions).

Dave