Description: There are two similar, and common, species of knotgrass in Northern Ireland - Polygonum aviculare sensu stricto and P. arenastrum. For convenience we have mapped them together as an aggregate but P. aviculare is the commoner. Both occur in open situations: e.g. as agricultural weeds; on pathways; on sandy or gravelly sea shores; in gravel or sand pits.

They are small-leaved, annual species with tiny white or pink flowers which produce shiny dark brown little nutlets. There are silvery, tattered sheaths around the stems at the base of each leaf. They normally grow flat against the ground.

All names: Polygonum aviculare agg. L.sensu lato

Distribution Map from NBN: Polygonum aviculare agg. at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Polygonum aviculare agg. at iNaturalist World Species Observations database.