I met this moss, Scouleria aquatica, on the bryology field trip before this year's botany conference. In its current state it doesn't look very aquatic. It was growing on the rocks at the edge of the river in a zone that would be completely flooded in the springtime. During that time of the year it grows as a completely submerged aquatic moss. For the other part of the year it is high and dry for months at a time. When dry, they are in a state of suspended animation. Not photosynthesizing or growing at all.
We added a bit of water to this patch and it made a dramatic change to the mosses appearance. The edges are gray, sandy, and dry, whereas the plants in the center are hydrated and green. It is amazing how rapidly mosses can take up water and start photosynthesizing.
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