Under what conditions can the most primitive plant form survive?

You will have to be more specific. What exactly do you mean by primitive
plants? If you mean one-celled plants, most of them are found in water. If you
mean primitive land plants, that usually means the mosses and their relatives.
Since their primitive structure lacks sophisticated water transporting
capability, they are mostly adapted to shady locations with a constant supply
of moisture.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)