Not to be semantically confused with : Branched Bur-Reed or Un-branched Bur-Reed nor with Burdocks such as Lesser Burdock (Arctium minus) nor with any of the Burnets such as Great Burnet (Sanguisorba officinalis) nor Bur Chervil (Anthriscus caucalis) or Pirri-pirri-bur (Acaena novae-zelandiae) [plants with similar names from different families]
Lookee-Likees : London Bur-Marigold but that has leaves without serrations and smaller non-drooping flower heads. Also similar to Trifid Bur-Marigold which does have serrated leaves, but that has lower leaves lobed in threes. Of these three, only Nodding Bur-Marigold might have ray florets on some specimens.
No relation to : Branched Bur-Reed nor with Un-branched Bur-Reed. And although they are in the Same Daisy Family, neither are they related to
Marigolds such as
Common Marigold which is in a differing Genus. [plants with similar names].
Nodding Bur-Marigold is more common than is London Bur-Marigold and grows beside fresh water, and in the margins of dry ponds, canals and reservoirs. There is a variety with large and bright-yellow ray florets called Bidens cernua var. radiata.
A POLYACETYLENE (POLYYNE)
Phenylheptatriyne (PHT) or 1-phenylhepta-1,3,5-triyne, is a poisonous phototoxic polyacetylene found in species of Beggartics and Bur-Marigolds of the Bidens genera such as London Bur-Marigold, and also found in species of the Dahlia genera, Blue Fleabane (Erigeron acris) and Tall Fleabane (Erigeron annuus) also contain PHT in the essential oils extracted from the roots as a major component (27 -37%), exceeded only by the c.50% concentration of Matricaria Ester. On exposure to UV light it is a phototoxic to bacteria and is also a fungicide and exhibits properties against cancer that may prove useful. It is very similar to Pontica Epoxide found in Yarrow (Achillea millefolium) but closes the
benzene ring and lacks an epoxide group.