1) Foreign 
introduced accidentally (usually referring to weeds).
a thing or person coming from outside
• (n.) A thing or person coming from without; an immigrant. • (a.) Accidental. • (a.) Adventitious.
see adventitious
In botany terminology, describes a plant which has been introduced to an area recently, in particular since colonisation by humans. ... (09 Oct 1997) ... 
Ad·ven'tive adjective 1. Accidental. 2. (Botany) Adventitious. Gray. 
Said of an introduced plant not yet established; imperfectly or only partially naturalized.
Not native and not fully established; locally or temporarily naturalized
[adj] - not native and not fully established
adjective not native and not fully established; locally or temporarily naturalized; `an adventive weed`
growing spontaneously