Polygonum oxyspermum

Tracheophyta MagnoliopsidaPolygonaceaePolygonumPolygonum oxyspermum


A prostrate annual, biennial or short-lived perennial of sand, shingle or shell beaches, sometimes found on other open sandy ground near the sea, usually just above the limit of the highest tides. Lowland.



World Distribution

European Wide-temperate element; also in N. America.

Broad Habitats

Supralittoral sediment (strandlines, shingle, coastal dunes)

Light (Ellenberg): 9

Moisture (Ellenberg): 6

Reaction (Ellenberg): 7

Nitrogen (Ellenberg): 8

Salt Tolerance (Ellenberg): 3

January Mean Temperature (Celsius): 4.6

July Mean Temperature (Celsius): 14.8

Annual Precipitation (mm): 1102

Height (cm): 20

Perennation - primary


Life Form - primary

Therophyte (annual land plant)



Clonality - primary

Little or no vegetative spread

Count of 10km squares in Great Britain: 305

Count of 10km squares in Ireland: 75

Count of 10km squares in the Channel Isles: 9

Atlas Change Index: 0.01

JNCC Designations


Scarce Atlas Account

Scarce Atlas Account: 

Polygonum oxyspermum C. Meyer & Bunge ex Ledeb.

Ray's knotgrass

Status: not scarce


This is a characteristic but local plant of strandlines on coastal sand, shingle and silty mud. Associated species include Atriplex glabriuscula, A. laciniata, Cakile maritima and Salsola kali. It also occurs above the strandline in embryonic foredunes.

It is an annual or short-lived perennial and is probably largely self-pollinated. It flowers from July to October.

This species has declined in some areas. It has always been rare in eastern England. Strandline plants are notoriously erratic in appearance (Webb & Akeroyd 1991), so disappearance from a particular locality does not always imply a decline. Nevertheless, this plant has suffered from the increased disturbance of many beaches, with consequent damage to strandline and foredune communities. It may be under-recorded on the west coast of Scotland.

The species occurs along most of the coasts of Europe, except southern and western Spain (Jalas & Suominen 1979). Subsp. raii extends from north-western Spain to arctic Russia, with almost indistinguishable plants from the coasts of the Black Sea having been called P. mesembricum. Subsp. oxyspermum, with longer, more greenish-brown fruits than subsp. raii, occurs in the Baltic and southern Norway. Longer-lived perennial plants from the western and central Mediterranean coasts belong to subsp. robertii (an epithet erroneously ascribed to British material in the past). 

The British plant is subsp. raii (Bab.) D. Webb & Chater. Some plants from Scotland, especially from Arran, are close to subsp. oxyspermum and require further investigation.


J. R. Akeroyd

Atlas text references

Atlas (173c)
Hultén E, Fries M
1986.  Atlas of north European vascular plants north of the Tropic of Cancer. 3 vols.
Jalas & Suominen (1979)
Lousley JE, Kent DH
1981.  Docks and knotweeds of the British Isles. Botanical Society of the British Isles Handbook no. 3.
Stewart A, Pearman DA, Preston CD
1994.  Scarce plants in Britain.
Styles BT
1962.  The taxonomy of Polygonum aviculare and its allies in Britain. Watsonia. 5:177-214.