The roots purpose in the elixer is unkown, but must have added a kick to it to make Adam forget his feeeling for Cassie and only remeber his relationship with her but not the love that they shared.
The origin of the page is unkown, but it is said that Cassie's mother wrote it down for an unkown purpose. But the creator of this page may be John Blackwell.
The root, however, has its limit - it cannot make a witch with dark magic forget their love for the other person just as in Cassie's case it made her very sad and lonely.
The root is mostly found in trees hollowed out by rot, this is the only main part of the elixir.
Please note that the persons mentioned above come from a novel and TV show