UNA NOVA ASSOCIACiÓ DE PLANTES AQUÀTIQUES ALS PIRINEUS: EL RANUNCULO ERADICATI-POTAMETUM ALPINI

SUMMARY A new association of aquatic plants from the Pyrenees: the Ranunculo eradicati-Potametum alpini. The Ranunculo eradicati-Potametum alpini, a new association of aquatic plants, is described from the subalpine pyrenean lakes. It is related to the Potametum filiformis from the Alpine range and it is dominated mainly by Potamogeton alpinus, P. berchtoldii and Ranunculus trichophyflus ssp. eradicatus. The association develops in soft-water lakes with a conductivity ranging from 15 to 78.2 IlS cm- 1 , water alkalinity ranging from 100 to 650 Ileq 1- 1 and calcium carbonate concen­ tration ranging from 59 to 331 Ilg-at 1- 1 • These values are relatively high when compared with other Pyrenean lakes where isoetid populations develop. Water alkalinity seems to be the main environmental factor determining the kind of aquatic macrophytic vegetation in Pyrenean lakes .