Latt,
Yup, I agree.
Of course, my experience with the close proximity occurance/nonoccurance in exact same environs, all come from hunting 'seng, as I am a new grower.
Here's an odd (not so odd when I thought it thru) one that I noticed several years ago: I was driving on a gravel road that I use every time that I go to my camp in the mountains. ... Along the high bank at the roads edge, I spotted many many companion plants. I knew the woods on both sides of the road, and other than a rare Jack in the Pulpit, there wasn't much of anything other than hay scented fern.
Anyway, I gave those woods another traipsing, and found those copses to be more or less the same as I knew them to be.
I got to thinking about all of that, and wondered, \"Why all those companions along that narrow band of high bank?\" ... Here's what I finally came up with: That area (3400' elevation) gets a lot of snow during Winters, and the road itself is sort of a main artery backroad. There is a State Road garage nearby, and they salt that road frequently throughout the Winter. I believe they inadvertedly treated the soil along that high bank in salting the road. Of course, road salt may not be the best of soil treatments, but it would most certainly make a difference, and I honestly can't think of any other reason as to why it would be that way.
I first noticed that occurance over 10 years ago, and it is still the same today. Other than a bare few on the lower side, the adjacent woods are still more or less barren of these plants.
The plants are Bloodroot, Both kinds of Cohosh, False Solomon's Seal, Trilliums, J.I.P. and Spikenard. I assume the seed got there either airborne and/or from wildlife. I have not ever seen a 'seng in there with these plants.
Bill