facultatively

/ˈfækəlˌteɪtɪvli/
adverb
  1. In a way that is optional or not required.
    • The assignment can be completed facultatively, so you may choose to do it for extra credit.
    • The software features are facultatively enabled by the user.
    • Membership fees are facultatively paid, meaning you can decide whether to contribute.
  2. In biology, in a manner that allows an organism to adapt to different conditions.
    • These bacteria grow facultatively in both oxygen-rich and oxygen-poor environments.
    • The plant behaves facultatively as an annual or perennial depending on the climate.
    • Some fungi live facultatively as saprophytes or parasites.
Antonyms
What does "facultatively" mean? | whatsthatwordmean | whatsthatwordmean