Many types of land mosses grow underwater.
It is necessary to clean land moss from any and all dirt before submerging it underwater in your main aquariums. Moss does not have roots.
So, probably the cleanest samples grow on rocks and walls…
Preparing Land Moss to Grow Underwater Update
Preparing Land Moss to Grow Underwater Update
Two Ways to Grow Land Moss Underwater, by Michael Langerman
Two Ways to Grow Land Moss Underwater, by Michael Langerman
Can you put outdoor moss in your aquarium? : r/PlantedTank
Growing Terrestrial Moss in Aquarium, by Michael Langerman
Preparing Land Moss to Grow Underwater Update
Two Ways to Grow Land Moss Underwater, by Michael Langerman
Land Moss Underwater and Above - by Michael Langerman
Two Ways to Grow Land Moss Underwater, by Michael Langerman
Two Ways to Grow Land Moss Underwater, by Michael Langerman