There's a number of factors involved; for some of the plants the creators wanted to keep them from easily being duplicated to keep them from being stolen. Others, simply require very specific conditions like the Treasure Trees; if one needs at least a thousand acres along a shallow bayou or bay swept by a nearby ocean current,then it's probably easier to take over ownership than try to transplant. Others simply need special nutrient conditions and care. And lastly, some represent technology that current Renaissance-level technology can't duplicate; nobody has any idea how to grow a living ship or city.

I also left out some of the most common and ubiquitous plants. Depending on the philosopher, the trees that have basins of clean, filtered water are included in the "Created" or Natural" category. And people would really rather forget the plant engineered to be a fence, made out of a latticework of bamboo, with thorns and poison ivy leaves. And of course monkey-cats and mimic parrots, while ubiquitous aren't really worth mentioning yet.