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Paspalum paspalodes

Annual herb, stoloniferous and with discrete flowers in inflorescences similar to small spikes.

Scientific namePaspalum paspalodes (Michx.) Scribn.

Common names: knotgrass, ditch-grass, jointgrass, water couch, wiregrass, mercer grass

FamilyPoaceae (Gramineae)

Status in Portugalinvasive species

Risk Assessment score: (in development)

SynonymyDigitaria disticha Fiori et Paol., Paspalum distichum L., Paspalum distichum auct., non L.

Nível de risco: (em desenvolvimento)

Last update: 11/07/2014

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How to recognise it

Annual herbstoloniferous, with culms up to 70 cm.

Leaveslinear (5-15 x 0,2-1 cm), with a ciliate blade on the margins; sheaths, at least the basal ones, ciliate on the upper surface; ligules of 2-3 mm.

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.


Similar species

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).


Geographic areas where there are records of Paspalum paspalodes

Other places where the species is invasive

Europe (Spain, Italy, Turkey, Albania, Bulgaria, France, Greece, Macedonia, Romania, United Kingdom, Ukraine), Australia, New Zealand.


Introduction reasons

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:


Physical control

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.


Chemical control

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">Invasive Alien species">Species Gateway (2012) Paspalum paspalodes. Available: http://www.europe-aliens.org/speciesFactsheet.do?speciesId=54559 [Retrieved 10/11/2012].

Dana ED, Sanz-Elorza M, Vivas S, Sobrino E (2005) Especies vegetales invasoras en Andalucía. Consejería de Medio Ambiente, Junta de Andalucía, Sevilla, 233pp.

Dufour-Dror J-M (2012) Alien invasive plants in Israel. The Middle East Nature Conservation Promotion Association, Ahva, Jerusalem, 213pp.

Gallastegui MH, Prieto JAC (2010) Flora alóctona invasora en BizkaiaInstituto para la Sostenibilidad de Bizkaia, Vizkaya, 196pp.

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].