Some qestions ablou the RPEM model

I want to know the difference between the state variable Rooted Plant Shoot, Rooted Plant Root and Rooted Plant Epiphyte, the three state variable stand for which specific aquatic plants? the publicly available material is scarce, can you expalin it to me ? thank you.

The RPEM sub-model calculations are based on mass of carbon from rooted plants in a certain area. This mass of carbon is not linked to a specific species of plant. Instead the RPEM model uses the mass of carbon as coming from four sources: 1. roots: from plants below the sediment interface, 2. shoots: living plants above the sediment interface3. epiphytes: bacteria and algae, the slime that are attached to the shoots4. detritus: dead plant material above the sediment interfaceThe mass of carbon is fractioned into these four groups and they can be from many different species of aquatic plant.

Thank you.