Stellaria graminea; the Lesser Stitchwort typically grows on (drier) gasslands, especially midst high grasses along roadsides, ditches and disturbed soils. It has been introduced and now found widespread near farms and other human settlements. As a Stellaria species, it can be readily characterised by the long stems and long narrow reaves (just a few mm broad and up to 2 cm long). It is a much-branched slender plant. The stems are not really strong enough to grow upwards but it uses grass-culms for stability.
It is a member of the Pink family (Caryophyllaceae). The Icelandic name of this species is Akurarfi.