YOU MUST DECLARE IT AND HAVE IT EXAMINED
To repeat: YOU MUST DECLARE IT AND HAVE IT EXAMINED
Please read the entire Answer carefully, I am in not suggesting OP smuggle or break the law in any way. I am also not going to provide references to every country's customs and agriculture rules.
It is not the case that plant materially is unconditionally forbidden, however, this is something that Customs and Agriculture Officials at your destination will have to determine.
Meaning, you can carry plant materials to the border, but upon arrival YOU MUST DECLARE IT AND HAVE IT EXAMINED.
If you declare it and it's not allowed, it will simply be confiscated and destroyed (provided it's not a dangerous or otherwise illegal substance). If you are caught smuggling it, it's a significant fine at the least.