ADVENTIVE
adventive
(adjective) not native and not fully established; locally or temporarily naturalized; “an adventive weed”
Source: WordNet® 3.1
Etymology
Adjective
adventive (comparative more adventive, superlative most adventive)
accidental
adventitious
(biology) Of a plant that is not native, but was introduced by humans to a place and has since become naturalized.
Noun
adventive (plural adventives)
A non-native plant that has become naturalized.
Source: Wiktionary
Ad*ven"tive, a.
1. Accidental.
2. (Bot.)
Definition: Adventitious. Gray.
Ad*ven"tive, n.
Definition: A thing or person coming from without; an immigrant. [R.]
Bacon.
Source: Webster’s Unabridged Dictionary 1913 Edition