Sphagnum

Peat
Sphagnum often grows in acidic marshes where there’s little decay. Over thousands of years, the dead sections of Moss and other marshy plants are slowly carbonized, compacted, and fossilized, resulting in a dark spongy material known as peat.
It is compressed, dried, and moved from blocks. Peat is employed pretty much as good manure to beat soil alkalinity and it increases water retention similarly to aeration of the soil.