Open and often unstable assemblies of herbaceous or suffrutescent pioneering plants, rich in casual immigrants from higher altitudes, colonizing gravel beds of the montane reaches of unregulated Alpine streams, with Chondrilla chondrilloides, often accompanied by Erucastrum nasturtiifolium, Gypsophila repens, Dryas octopetala, Aethionema saxatile, Epilobium dodonaei, Erigeron acer, Leontodon berinii, Buphthalmum salicifolium, Euphorbia cyparissias, Fumana procumbens, Agrostis gigantea, Anthyllis vulneraria ssp. alpestris, Campanula cochlearifolia, Hieracium piloselloides, Calamagrostis pseudophragmites, Conyza canadensis, Pritzelago alpina, and seedlings of Salix elaeagnos, Salix purpurea, Salix daphnoides and Myricaria germanica. Because of widespread interference with natural flow regimes, these formations are gravely endangered.