Elsach flow falkensteiner cave baden-wuerttemberg swabian alb grabenstetten bad urach water cave karst active water cave canyon stone moss mossy green overgrown naturally forest forest floor rock cratoneuron filicinum fern-like strong-nerved moss deciduous moss amblystegiaceae strong nervous moss common strong-nerved moss changeable strong-nerved moss palustriella commutata cratoneuron commutatum