Annual herb, stoloniferous and with discrete flowers in inflorescences similar to small spikes.
Scientific name: Paspalum paspalodes (Michx.) Scribn.
Common names: knotgrass, ditch-grass, jointgrass, water couch, wiregrass, mercer grass
Family: Poaceae (Gramineae)
Status in Portugal: invasive species
Risk Assessment score: (in development)
Synonymy: Digitaria disticha Fiori et Paol., Paspalum distichum L., Paspalum distichum auct., non L.
Nível de risco: (em desenvolvimento)
Last update: 11/07/2014
How to recognise it
Inflorescences: with 2 (rarely 4) digitate, spiciform clusters, green, each one with 1,5-7 cm, 1 ± sessile and another with a peduncle; inferior chaff inferior frequently reduced to a small scale, the upper one much larger, herbaceous, with a protruded midrib ; black stigmas.
Fruits: caryopses with an ellipsoidal shape.
Flowering: August to September.
Paspalum vaginatum Swartz (seashore paspalum) is similar but the spikes have 2 developed peduncles. Other species of Paspalum (as for species of the genus Cynodon, with a haired ligule), Echinochloa (without a ligule) and Digitaria are relatively similar but they normally have more than two spikes.
Characteristics that aid invasion
It propagates vegetatively, by stolons that have great capacity to root.
It also propagates by seed (although less frequently), producing a high number of seeds (1 to 3 generations of seeds/year).
Native distribution area
Africa, South and North America.
Distribution in Portugal
Mainland Portugal (Minho, Trás-os-Montes, Douro Litoral, Beira Litoral, Beira Alta, Estremadura, Ribatejo, Alto Alentejo, Baixo Alentejo, Algarve), Azores archipelago (all islands), Madeira archipelago (Madeira Island).
Other places where the species is invasive
Europe (Spain, Italy, Turkey, Albania, Bulgaria, France, Greece, Macedonia, Romania, United Kingdom, Ukraine), Australia, New Zealand.
Fodder for animals.
Preferential invasion environments
Humid places, like banks of watercourses, crop fields or rice fields – both in natural environments and with human influence.
It tolerates intensive grazing and fire, but it needs water to recuperate.
It does not tolerate frost well.
Impacts on ecossystems
It forms dense mats, affecting the native vegetation.
Natura 2000 network habitats more subject to impacts
Paradoxically, this invasive species was considered as a bio-indicator of two Natura 2000 Network habitats, where it proliferates:
– Constantly flowing Mediterranean rivers with Paspalo-Agrostidion species and hanging curtains of Salix and Populus alba (3280);
– Intermittently flowing Mediterranean rivers of the Paspal-Agrostidion (3290).
Controlling an invasive species demands a well-planned management, which includes the determination of the invaded area, identifying the causes of invasion, assessing the impacts, defining the intervention priorities, selecting the adequate control methodologies and their application. Afterwards it is fundamental to monitor the efficiency of the methodologies and recuperation of the intervened area as to perform, whenever necessary, the follow-up control.
The control methodologies used for Paspalum paspalodes include:
Hand pulling (preferencial methodology): It is applied to plants of all sizes. Because it is a species that is frequent in humid places hand pulling is usually easy; however, if in more compacted substrates, hand pulling must be made during the rainy as to facilitate the removal of the root system. As much as possible, it should be guaranteed that there are no large roots/fragments left in the ground.
Soil Solarisation. It’s an alternative to hand pulling, mainly in extensive areas that are invaded by the species. It should be guaranteed that no native species are affected.
Foliar application of herbicide. Spray with herbicide (active substance: glyphosate) limiting its application to the target species.
Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.
DAISIE European Invasive Alien Species Gateway (2012) Paspalum paspalodes. Available: http://www.europe-aliens.org/speciesFactsheet.do?speciesId=54559 [Retrieved 10/11/2012].
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Dufour-Dror J-M (2012) Alien invasive plants in Israel. The Middle East Nature Conservation Promotion Association, Ahva, Jerusalem, 213pp.
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Marchante E, Freitas H, Marchante H (2008) Guia prático para a identificação de plantas invasoras de Portugal Continental. Imprensa da Universidade de Coimbra, Coimbra, 183pp.
Silva L, Corvelo R, Moura M, Land EO, Jardim R (2008) Paspalum distichum L. In: Silva L, Land EO, Luengo JLR (eds) Flora e fauna terrestre invasora na Macaronésia. Top 100 nos Açores, Madeira e Canárias. Arena, Ponta Delgada, pp. 472-474.
USDA, NRCS. (2012) The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA. Available: http://plants.usda.gov [Retrieved 10/11/2012].
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