Hi Evan,
Thank you for the question! I have not heard of a "Guardian Plant" before... but I did look it up. It looks to be the same as a companion plant. Looks like they are mainly talking about certain plants that will attract beneficial insects or pull the pests to them in order to save another plant... such as using marigold to attract thrips away from crops. I've only skimmed over the info but that's what I get out of it. Very interesting, thanks again for posting!
Here's a couple of links I found:
http://www.ballpublishing.com/...
http://www.youtube.com/watch?v...
