Moss

With no vascular system, all-over photosynthesis, and spores for reproduction, you become a small, low-rise plant, which requires a wet environment to survive.  You are a moss.

Mosses are amazing plants.  Some can withstand dessication for months and then start photosynthesising again without hours of rainfall.  Some produce scents to attract micro-insects which spread their spores. Mosses grow across the world, wherever there is (sometimes) moisture.

Spagnum moss has even managed to colonise the acidic water found over the surface of peat bogs.  In order to do this it has developed another mutation - dead cells containing water supplies.

In growing quickly, wherever there is damp, mosses have become an important part of the process of greening.  Mosses grow over newly damp ground and keep moisture in, which enables other plants to follow.

That's as far as you can evolve here!  
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