Beggarticks - Bidens frondosa

Description

Very similar to Trifid Bur-marigold (Bidens tripartita) but taller (to 1 metre) the leaves mostly pinnate with 3 to 5 separate leaflets. Flowerheads 10 to 20 mm outer flower bracts shorter than the blackish inner ones, rarely leaf-like. The lower leaves have an unwinged petiole, the terminal leaflet has a long, unwinged stalk. The tapered achenes have forwards-pointing barbs. Detailed examination of the plant is necessary for a safe id.

Similar Species

Bidens tripartita and Bidens cernua; other Bidens are known to be naturalised in Britain and may turn up.  Identification is tricky and the key in Stace (4th edition) should be referred to; details of leaf and leaflet shape, and the shape of the achenes, is usually needed.

Identification difficulty
ID guidance

Many leaves pinnate, with lateral leaflets; the lower leaves with unwinged petioles and with main apical leaflet with a distinct more or less unwinged stalk; barbs on edge of achenes forward-directed. (Note that Stace (4th edition) is not entirely certain that the achenes always have the latter characteristic) 

Recording advice

A photo of the whole plant and details of leaf shape and achenes.  Note that this plant cannot be verified from a photo just of the flowers

Habitat

Found by rivers and canals, on damp and waste ground, and on tips in urban areas and ports.

When to see it

In flower during June, August, September and October.

Life History

Annual.

UK Status

Occasional in Britain but is now becoming more frequently naturalised by canals in the English Midlands.

VC55 Status

Uncommon but possibly increasing in Leicestershire and Rutland. It was first recorded in our area in 1988.

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Leicestershire & Rutland Map

MAP KEY:

Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015

UK Map