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Trifid Bur-Marigold

Trifid Bur-Marigold

Bidens tripartita

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How common: Common

Alien species

Trifid Bur-Marigold is a small annual of wet, muddy places. It has brownish to reddish stems and leaves usually split into three narrow parts. The plant carries small, upright yellow flower heads without a showy ring of petals, and the hooked two-pronged seeds stick to fur and clothes.

Did you know?

  • Its two-pronged, barbed seeds readily cling to animals and clothing, spreading the plant far and wide.
  • It can hybridise with the showier Bidens radiata.

About the species

Identification

Annual 10–60 cm tall, often much branched. Stems dark brown to reddish, mostly smooth. Leaves grow in pairs at the same level on the stem, short-stalked, usually divided into three narrow parts with coarse teeth; sometimes more cut, rarely undivided. Flower heads are single, upright, on long stalks, 1–2 cm across; they show only tiny yellow flowers in the center and no petal-like outer ring. Seeds are flat, brown, with two short barbed prongs at the tip that stick to fur or clothing. Differs from Bidens radiata, which has a ring of pale yellow petals. Flowers in Finland from August to September.

Plant group

Herbaceous plants

Habitat

shore

Flowering

Aug–Sep

About the habitat

Grows on riverbanks, lake and pond edges, ditches, puddles, fallow or waste ground, farmyards and other disturbed, nutrient-rich soils that stay wet at least part of the season. Common in southern Finland, becoming rarer toward central Finland; only occasional in Lapland.

Sources

Photo: Екатерина Гущина, CC BY 4.0 https://www.gbif.org/occurrence/6320724959

Text: Pinkka: Verso- ja leviäintunnistus - Kaikki leviäimet, CC BY 4.0 https://laji.fi/taxon/MX.39779

Text: Pinkka: Verso- ja leviäintunnistus - Kaikki versot, CC BY 4.0 https://laji.fi/taxon/MX.39779

Text: Pinkka: Laaja maatalouslajintuntemus 4 op - Koppisiemeniset, CC BY 4.0 https://laji.fi/taxon/MX.39779

Text: Wikipedia (Finnish), CC BY-SA 4.0 https://fi.wikipedia.org/wiki/Tummarusokki

See also