The Art of Simpling -- what is the etymology of "simpling"?

I read a 1657 book called the Art of Simpling by William Coles. Wiktionary says Simpling is "an expedition to gather plants; a herborizing."

I wondered if it was a variation of sampling, but Wiktionary says it comes from simple. I was wondering if anyone had any insight into the origin of this word.

https://redd.it/1x1l36h
@r_etymology