I understand that obligate symbioses means that the two organisms cannot live without each other and are in a symbiotic relationship, but do green algae from this with fungi?


Yes, Lichen are composite organisms of green algae (or cyanobacteria) living togther with fungi.

In most cases the fungi-part is completely dependent on that symbioses and is completely dependent on the symbiosis. For the algae it seems that some species can survive on their own, but not necessarily in the same enviroment as the lichen, while other species may again be completely depedent on the symbiosis (see also the comments).

  • $\begingroup$ The wiki page you quoted states "The photosynthetic partner [so the algae] can exist in nature independently of the fungal partner, but not vice versa." That contradicts your answer, don't you agree? $\endgroup$ – RHA Nov 18 '18 at 20:55
  • $\begingroup$ @RHA, this quote does indeed contradict my takeaway from the part/quote is was focusing on: "Although some photosynthetic partners in a lichen can survive outside the lichen, the lichen symbiotic association extends the ecological range of both partners, whereby most descriptions of lichen associations describe them as symbiotic". I guess for the algae/cyanobacteria it really depends on the exact species and environment whether they'd be able to survive on their own. $\endgroup$ – Nicolai Nov 19 '18 at 11:49
  • $\begingroup$ It seems that way, but it might also be unknown. Maybe add some doubt to your answer? $\endgroup$ – RHA Nov 19 '18 at 12:56
  • $\begingroup$ @RHA I (hopefully) clarified it a bit $\endgroup$ – Nicolai Nov 19 '18 at 15:05

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