Juncus articulatus; The Jointed rush can be found on moist soils and along streams. This rush can be identified by the spreading stalks above the foliage bearing a cluster of flowers. A very similar species is Junus alpinoarticulatus, the Alpine Rush. The Jointed Rush can be identified by the spreading flower stalks (not clear though when young), the lower outer stems more or less spreading horizontally and the stems are usually reddish on the bottom.
It is a member of the rush family (Juncaceae).