Total cover of the submerged layer in percent. Includes rooted or drifting plants that by-and-large remain submerged in the water column or on the aquatic bottom (e.g., pondweed). The focus is on the overall strata arrangement of these aquatic plants. Note that emergent plants life forms in a wetland should be placed in above water strata (e.g., cattail or sedges would be placed in the herb stratum, whereas the duckweed would be in the floating aquatic stratum).