Weed Seed: Galium aparine (Cleavers)

Family

Rubiaceae

Common Name

Cleavers

Regulation

Secondary Noxious, Class 3 in the Canadian Weed Seeds Order, 2016 under the Seeds Act.

Distribution

Canadian: Occurs across Canada except in NU and YT (Brouillet et al. 2016Footnote 1).

Worldwide: Native to Eurasia and North America and widely naturalized, found in temperate zones throughout the world and at higher altitudes in the tropics (Malik and Vanden Born 1988Footnote 2, CABI 2016Footnote 3, USDA-ARS 2016Footnote 4). Occurs throughout North America from Alaska to the east coast (Malik and Vanden Born 1988Footnote 2, CABI 2016Footnote 3, USDA-NRCS 2016Footnote 5), with both native and introduced populations present in Canada (Brouillet et al. 2016Footnote 1).

Duration of Life Cycle

Annual

Seed or Fruit Type

Schizocarp, divided into 2 fruits

Identification Features

Size

  • Fruit diameter: 1.6 - 4.0 mm

Shape

  • Fruit globose with a prominent hole on the ventral side

Surface Texture

  • Fruit surface is covered in hooked bristles with tuberculate bases, rarely smooth

Colour

  • Fruit grey-brown with white bristles

Other Features

  • The hole on the ventral side of the fruit is typically round and deeply-set

Habitat and Crop Association

Arable land, particularly grain fields, fence rows, barnyards and pastures. Also found in deciduous woods, thickets and rocky coastal bluffs, parklands, shores and waste ground (Malik and Vanden Born 1988Footnote 2, Darbyshire 2003Footnote 6). Thrives in moist, well drained habitats, in loam and sandy loam soils (Malik and Vanden Born 1988Footnote 2).

General Information

Cleavers may have been introduced to North America in grain fields by early settlers who imported contaminated seed from Eurasia (Malik and Vanden Born 1988Footnote 2). It can also be transported by harvesting equipment and animals (Ministry of Agriculture, Food, and Fisheries 2002Footnote 7).

A single plant can produce up to 3,500 seeds that remain viable for up to 6 years in the soil (Ministry of Agriculture, Food, and Fisheries 2002Footnote 7). The spiny-hooked fruit is adapted to animal dispersal (Malik and Vanden Born 1988Footnote 2).

Similar Species

False cleavers (Galium spurium)

  • The fruits of false cleavers and cleavers both have a globose shape with a hole on the ventral side, a grey-brown colour, and dense, white bristles.
  • False cleavers (diameter: 1.0 - 2.5 mm) are generally smaller than cleavers; the bristles have a non-tuberculate base, and the hole is usually a transverse oval.

Photos

Cleavers (Galium aparine) fruits
Cleavers (Galium aparine) fruit
Cleavers (Galium aparine) fruit
Cleavers (Galium aparine) fruit and tubercles
Cleavers (Galium aparine) fruit, hilum view
Cleavers (Galium aparine) fruit
Cleavers (Galium aparine) fruit, cross-section
Cleavers (Galium aparine) fruit, close-up of surface

Similar species

Similar species: False cleavers (Galium spurium) fruits
Similar species: False cleavers (Galium spurium) fruit
Similar species: False cleavers (Galium spurium) fruit, close-up of surface
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