1. Family: Polygonaceae Juss.
    1. Genus: Polygonum L.
      1. Polygonum maritimum L.

        This species belongs to the knotgrass family, Polygonaceae. The common name, knotgrass, refers to the swollen nodes of the stems which appear as joints or knots.

    [KSP]

    Kew Species Profiles

    General Description

    Sea knotgrass is a coastal plant and is the rarest of the knotgrasses in Britain.

    This species belongs to the knotgrass family, Polygonaceae. The common name, knotgrass, refers to the swollen nodes of the stems which appear as joints or knots.

    Species Profile
    Geography and distribution

    Polygonum maritimum is native to a few coastal sites in southern England, the Channel Islands and one locality in southern Ireland, but it is also found on the west coast of France southwards to the Mediterranean region, and Macaronesia.

    Description

    Overview: The sea knotgrass is a perennial, with herbaceous weak stems that are woody below and grow up to 50 cm in length; the stems are procumbent.

    Leaves: The leaves are somewhat oblong and leathery in texture with inrolled margins. The leaf stipules are a very conspicuous and characteristic part of the plant; they are silvery, forming a sheath at the base of leaves and cover part of the stem.

    Flowers:  The flowers are in inflorescences in the axils of leaves and are reddish or pink with five perianth lobes about 4 mm long.

    Fruits: The fruit (achene) is dark brown, shiny and is longer than the perianth.

    The flowering and fruiting period is July-September.

    Threats and conservation

    Polygonum maritimum is the rarest of the knotgrasses in Britain. It is sporadic along the coast of Cornwall, Devon, Hampshire (including the Isle of Wight) and the Channel Islands. Since the 1960s its range has extended in England, its recent spread correlated with a run of mild winters and hot summers.

    Uses

    The leaves of the sea knotgrass are used as a dressing for burns. Perhaps in view of the recent extension of its range in England which is reported to be correlated with changes in the climate, it could act as an indicator species for climate change.

    Millennium Seed Bank: Seed storage

    Kew's Millennium Seed Bank partnership aims to save plant life world wide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.

    Number of seed collections stored in the Millennium Seed Bank: Six

    Seed storage behaviour: Orthodox (the seeds of this plant survive being dried without significantly reducing their viability, and are therefore amenable to long-term frozen storage such as at the MSB)

    Germination testing: Successful

    Distribution
    France, Ireland, United Kingdom
    Ecology
    Sandy beaches
    Conservation
    Rare
    Hazards

    Not known

    [KSP]
    Use
    Dressing for burns. Potential as an indicator species for climate change.

    Images

    Distribution

    Native to:

    Albania, Algeria, Azores, Baleares, Bulgaria, Canary Is., Cape Provinces, Corse, East Aegean Is., Egypt, France, Great Britain, Greece, Ireland, Italy, Kriti, Krym, Libya, Madeira, Morocco, Netherlands, Portugal, Romania, Sardegna, Sicilia, Spain, Tunisia, Turkey-in-Europe, Yugoslavia

    Introduced into:

    Argentina Northeast, Argentina Northwest, Argentina South, Chile Central, Chile South, Falkland Is.

    Common Names

    English
    Sea knotgrass

    Polygonum maritimum L. appears in other Kew resources:

    Date Identified Reference Herbarium Specimen Type Status
    Lewis, R. [540], Falkland Is. K000299181
    s.coll. [s.n.], Massachusetts K000831005

    First published in Sp. Pl.: 361 (1753)

    Accepted by

    • Dobignard, A. & Chatelain, C. (2013). Index synonymique de la flore d'Afrique du nord 5: 1-451. Éditions des conservatoire et jardin botaniques, Genève.
    • Akeroyd, J.R. (2013). Docks and Knotweeds of Britain and Ireland: 1-258. Botanical Society of Britain and Ireland.
    • Authier, P. & Covillot, J. (2011). Catalogue actualisé des plantes de l'île de Rhodes (Grèce) Saussurea; Travaux de la Société Botanique de Genève 41: 131-170.
    • Mateos, M.A. & Valdés, B. (2009). Catálogo de la flora vascular del Rif occidental calizo (N de Marruecos). I Selaginellaceae - Rosaceae Lagascalia 29: 105-257.
    • Zuloaga, F.O., Morrone, O. , Belgrano, M.J., Marticorena, C. & Marchesi, E. (eds.) (2008). Catálogo de las Plantas Vasculares del Cono Sur Monographs in Systematic Botany from the Missouri Botanical Garden 107: 1-3348. Missouri Botanical Garden.
    • Broughton, D.A. & McAdam, J.H. (2005). A checklist of the native vascular flora of the Falkland Islands (Islas Malvinas): New information on the species present, their ecology, status and distribution Journal of the Torrey Botanical Society 132: 115-148.
    • Lambion, J., Delvosalle, L. & Duvigneaud, J. (2004). Nouvelle flore de la Belgique du G. D. de Luxembourg, du Nord de la France et des régions voisines, ed. 5: 1-1167. Edition du Patrimoine du Jardin botanique national de Belgique.
    • Germishuizen, G. & Meyer, N.L. (eds.) (2003). Plants of Southern Africa an annotated checklist Strelitzia 14: 1-1231. National Botanical Institute, Pretoria.
    • Boulos, L. (1999). Flora of Egypt 1: 1-419. Al Hadara Publishing, Cairo.
    • Tutin, T.G. & al. (eds.) (1993). Flora Europaea ed. 2, 1: 1-581. Cambridge University Press.

    Literature

    Kew Species Profiles
    • Preston, C.D., Pearman, D.A. & Dines, T.A. (eds) (2002). New Atlas of the British and Irish Flora: An atlas of the vascular plants of Britain, Ireland, the Isle of Man and the Channel Islands. Oxford University Press, Oxford.
    • Clapham, A.R., Tutin, T.G. & Warburg, E.F. (1962). Flora of the British Isles. Cambridge University Press, Cambridge.
    • Uphof, J.C. Th. (1959). Dictionary of Economic Plants. Engelmann, New York.
    Kew Backbone Distributions
    • Dobignard, A. & Chatelain, C. (2013). Index synonymique de la flore d'Afrique du nord 5: 1-451. Éditions des conservatoire et jardin botaniques, Genève.
    • Authier, P. & Covillot, J. (2011). Catalogue actualisé des plantes de l'île de Rhodes (Grèce) Saussurea; Travaux de la Société Botanique de Genève 41: 131-170.
    • Mateos, M.A. & Valdés, B. (2009). Catálogo de la flora vascular del Rif occidental calizo (N de Marruecos). I Selaginellaceae - Rosaceae Lagascalia 29: 105-257.
    • Zuloaga, F.O., Morrone, O. , Belgrano, M.J., Marticorena, C. & Marchesi, E. (eds.) (2008). Catálogo de las Plantas Vasculares del Cono Sur Monographs in Systematic Botany from the Missouri Botanical Garden 107: 1-3348. Missouri Botanical Garden.
    • Broughton, D.A. & McAdam, J.H. (2005). A checklist of the native vascular flora of the Falkland Islands (Islas Malvinas): New information on the species present, their ecology, status and distribution Journal of the Torrey Botanical Society 132: 115-148.
    • Germishuizen, G. & Meyer, N.L. (eds.) (2003). Plants of Southern Africa an annotated checklist Strelitzia 14: 1-1231. National Botanical Institute, Pretoria.
    • Boulos, L. (1999). Flora of Egypt 1: 1-419. Al Hadara Publishing, Cairo.
    • Tutin, T.G. & al. (eds.) (1993). Flora Europaea ed. 2, 1: 1-581. Cambridge University Press.

    Sources

    Kew Backbone Distributions
    The International Plant Names Index and World Checklist of Selected Plant Families 2018. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
    [A] © Copyright 2017 World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

    Kew Names and Taxonomic Backbone
    The International Plant Names Index and World Checklist of Selected Plant Families 2018. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
    [B] © Copyright 2017 International Plant Names Index and World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

    Kew Species Profiles
    Kew Species Profiles
    [C]
    [D] http://creativecommons.org/licenses/by-nc-sa/3.0