Out of 15 or so seeds I have played on I only found 2. It is nice they are rare and makes finding one special... but it really is more of a pain to be forced to build around them.

It would be nice if there were more... or if you find and destroy/deconstruct one it gives you the ability to build them.

I destroyed the first one I found hoping it would give me the crafting recipe, the only other one I found was in a lousy place for anything but a portal hub/farm.