(N)  Native
A Native plant is one which has been growing in the area without being introduced by man usually for many thousands of years. It includes naturally occurring hybrids even if those have only recently been discovered.

(AR)  Archaeophyte
An Archaeophyte is an established plant believed to have been introduced by man before 1500 AD.

(NE)  Neophyte
A Neophyte has been introduced and naturalised after 1500 AD.

(CA)  Casual Alien
A Casual alien is a plant which grows in an area without being planted but fails to establish itself in the wild for very long.