adventitious

adjective4

1. •
   From an external source; not innate or inherent, foreign.
2. •
   Not congenital; acquired.
3. •
   Accidental, additional, appearing casually.

   • In a triad of verbs that admits nothing adventitious, Judah sees, takes, and lies with a woman; […] — 1981
4. •
   Developing in an unusual place or from an unusual source.

   • The Velloziaceae have evolved a woody stem which is covered with a layer of adventitious roots mingled with the fibres of the old leaf sheaths — 1985