Weed Seed: Nassella trichotoma (Serrated tussock)

Invasive Plant - Serrated tussock (Nassella trichotoma)



Common name

Serrated tussock


Prohibited Noxious, Class 1 in the Canadian Weed Seeds Order, 2016 under the Seeds Act. All imported and domestic seed must be free of Prohibited Noxious weed seeds.

Listed on the List of Pests Regulated by Canada established under the Plant Protection Act.


Canadian: Absent from Canada (Brouillet et al. 2016Footnote 1).

Worldwide: Native to southern South America and introduced to Australia, New Zealand, South Africa, and, very locally, into Europe (CFIA 2012Footnote 2).

Duration of life cycle


Seed or fruit type


Identification features


  • Floret length: 1.5 - 3.0 mm
  • Floret width: 0.6 - 1.0 mm
  • Awn length: 25.0 - 42.3 mm


  • Oval-shaped floret compressed laterally with a pointed base and flat top

Surface texture

  • Floret surface glossy, covered with tubercles that increase in size towards the top


  • Floret is straw yellow

Other features

  • Awn extends from the top of the floret
  • Floret base is surrounded by white bristles

Habitat and crop association

Pastures, grasslands, open forests (CFIA 2012Footnote 2). In Australia, it has spread over millions of hectares of pastureland (CFIA 2014Footnote 3).

General information

Serrated tussock is a tall, tussock-forming plant that out-competes native species and reduces biodiversity (Carr et al. 1992Footnote 4). The species spreads by seeds that are shed from the panicles as they tumble along the ground and then remain viable in the soil (Westbrooks and Cross 1993Footnote 5). The majority of the seeds are produced from self-pollinating florets, creating clones of the parent plant (Osmond et al. 2008Footnote 6).

Similar species

Uruguayan rice grass (Piptochaetium montevidense)

  • Florets are a similar size, oval shape with a tuberculate surface like serrated tussock.
  • Uruguayan rice grass florets are dark brown and have ridges on the surface, unlike the straw coloured and tuberculate serrated tussock florets.


Serrated tussock (Nassella trichotoma) florets
Serrated tussock (Nassella trichotoma) floret
Serrated tussock (Nassella trichotoma) floret, side view
Serrated tussock (Nassella trichotoma) the base of the floret
Serrated tussock (Nassella trichotoma) spikelets in panicle
Serrated tussock (Nassella trichotoma) floret
Serrated tussock (Nassella trichotoma) floret

Similar species

Similar species: Uruguayan rice grass (Piptochaetium montevidense) florets
Similar species: Uruguayan rice grass (Piptochaetium montevidense) floret
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