Equisetum palustre; As its name suggests the Marsh Horsetail grows in bogs and marshlands. The Icelandic name is Mýrelfting. In spring (early summer) the plants produce sporangial cones on top of green shoots. These shoots at first have very small side branches. These side branches grow fully later on. By then the plants can easily be confused with E. arvense (Field Horsetail). This is how you can tell them apart: the first (bottom) segment of the side branches are shorter than the sheath on the main stem in E. palustre ( Marsh Horsetail) where in E. arvense (Field Horsetail) they are longer. It is a common plant on Iceland.
FLORA OF ICELAND elements: Equisetum palustre, marsh horsetail