The closest to mangrove one can go in Finland. A black alder swamp. (Protected by Forest Law).
The moss-layer: e.g. Sphagnum warnstorfii, Sphagnum centrale, Sphagnum riparium,.Helodium blandowii, Others: Calla palustris, Caltha palutsris, Athyrium filix-femina, Carex vesicaria, Carex rostrata, Dryopteris expansa, Diplazium sibiricum, Equisetum fluviatile,