Leaves not lobed; achenes scarcely flattened with warty ridges in between (Stace, 4th edition).   Notes that there is some discrepancy between various sources concerning the appearance of the achenes. 

Other Bidens; especially B tripartita and B cernua. 

This is a very difficult genus, and we recommend that your specmen is examined by an expert before record in sent to NatureSpot.  Please retain a specimen of a flower in fruit in order that the achenes can be examined, and photograph the plant in its habitat, includng upper and lower leaves.

By canals

Established in the London area

Rare; more records likely as it spreads throughout the canal network