Carex norvegica; the Close-headed Alpine-sedge (in the America's known as Scandinavian Sedge) grows wide-spread in heathers and grasslands, never in large numbers though. Characteristic are the very short-stalked (sessile) brown/blackish-coloured spikes on top of a straight vertical stem (no more than 30 cm tall). The top spike is slightly larger than the lateral spikes. Other similar species on Iceland either have less contracted inflorescences, or the stems curve down to some degree, or have other coloured spikes.
It is a member of the sedge family (Cyperaceae). The Icelandic name of this species is Fjallastör.