Vegetation of vesicular lava cavities in Northern Iceland

Vesicular cavities in the lava fields of Northern Iceland communicate by small openings with the ground surface. Aeolian sediments, called the Icelandic Ioess, deposit over the bottom of these cavities, together with the reduced light intensity and equable microclimate, create specific biotopes occupied by sciophilous bryophytes andCystopteris fragilis. A new association within the allianceCtenidion Stefureac 1941—Cystopteri-Distichietum capillacei Bla?ková ass. nova— is described in the present paper.