The main species that grows in California is Artemisia vulgaris
. It is pretty common, and I see it when walking around wet or riparian areas. There are many, many species of Artemisia
, including the sagebrushes and wormwoods. Apparently, mugwort does not have the bitter oil (thujone?) of wormwood, but it still has a lot of aromatic properties.
I have also read of an east coast species of mugwort whose flavor and aroma are mellower than what grows here. It was likely introduced from Europe, which means it was likely the mugwort that was used in brewing in Europe before the days of hops. I'm sure you can use the California mugwort in brewing, you just might have to experiment with the amount and go lightly at first.
This thread is old now... have you done any brewing with mugwort yet? I'm sure you've seen this recipe: http://www.homebrewtalk.com/f76/mugwort-anti-imperial-stout-90441/
It hasn't made it to the front of my brew queue yet, but I've been curious about it for a while.