soybean oil comes from the soybean plant,
canola oil comes from the canola seed (i don't recommend high amounts of this for soap)
Safflower doesn't that come from the safflower flower or something?
Just to name a few, so there are several oils that do come from plants,
Not sure how you would DIY (do it yourself) to render the oils from the plant, weed or otherwise,
If i knew how to gather that soybean oil from the soybean i'd be out in the middle of the night out in my brothers soybean field! (he does ALL of his soaps from me free of charge as well as part of his christmas gift, you know the one, free soaps for the year, the last time he bought soap for himself was a couple of years ago, lol his wife on the other hand is another story! But she's just witch who just doens't like me so i don't give her any of my goodies, but i love giving my big bro great smelling man soaps !!!!!!!!!!!!!