NODDING BUR-MARIGOLD

Bidens cernua

Daisy & Dandelion Family [Asteraceae]

Flowers:
month8jul month8july month8aug month8sep month8sept month8oct

Pappus: pappusZpossible (3 to 4 bristles, tapered, backwards-directed barbs)
pappus8aug pappus8sep pappus8sept pappus8oct

status
statusZnative
 
flower
flower8yellow
 
inner
inner8brown
 
petals
petalsZ0 petalsZmany
(many)
type
typeZclustered
 
stem
stem8round
 
sex
sexZbisexual
 

18th Sept 2008, Failsworth, Rochdale Canal. Photo: © RWD
Growing in a partially drained canal bed. Up to 2 feet tall with serrated leaves in opposite pairs. Flowers are mostly without ray florets (but some specimens do have them, unlike London Bur-Marigold).


18th Sept 2008, Failsworth, Rochdale Canal. Photo: © RWD
Flower heads larger than London Bur-Marigold, and drooping as a result. Stalkless but saw-toothed leaves which are longer and narrower than those of London Bur-Marigold.


18th Sept 2008, Failsworth, Rochdale Canal. Photo: © RWD
Unlike London Bur-Marigold not all flower heads are without rayed florets (but this specimen is).


18th Sept 2008, Failsworth, Rochdale Canal. Photo: © RWD
Leaves toothed like Trifid Bur-Marigold and not untoothed as is London Bur-Marigold. All leaves of Nodding Bur-reed taper to their base, but are without stalks (i.e. are sessile).


18th Sept 2008, Failsworth, Rochdale Canal. Photo: © RWD
A single flower head perches atop each branched flowering stem. Behind this are seven to eight long narrow un-toothed bracts whereas in London Bur-Marigold there are about six.


18th Sept 2008, Failsworth, Rochdale Canal. Photo: © RWD
The serrated un-stemmed leaves are in opposite pairs.


18th Sept 2008, Failsworth, Rochdale Canal. Photo: © RWD
The bracts of the heavier nodding flowerheads are splayed backwards and thus upwards. Many flowers are on long stalks unlike those London Bur-Marigold.


18th Sept 2008, Failsworth, Rochdale Canal. Photo: © RWD
The disc florets are more numerous than those in London Bur-Marigold. Note the green stripes mostly on the inner yellow bracts.


18th Sept 2008, Failsworth, Rochdale Canal. Photo: © RWD
This specimen has eight long bracts.


18th Sept 2008, Failsworth, Rochdale Canal. Photo: © RWD
Within the inner yellow bracts with green stripes lie the disc florets, which are also striped.


18th Sept 2008, Failsworth, Rochdale Canal. Photo: © RWD
The lower leaves have two (or two pairs) of petioles at the stalkless base where leaf meets stem.


31st Aug 2019, Whitlinglam, nr. Norwich, Norfolk. Photo: © Carl Reynolds
The achenes (seed capsules) have from 3 to 4 bristles at the opening end a strongly-flattened and tapered case (only scarcely flattened and less than twice as wide as thick for London Bur-Marigold). They are greater than twice as wide as they are thick. Between the two to four ridges are smooth (warty for London Bur-Marigold). But the 3 to 4 bristles only applies to those florets taken from the central area; those taken from near the periphery can have fewer bristles; but the number of bristles is not a reliable guide to ID anyway.




The rarer RAYED FORM
Bidens cernua var. radiata

Common in Central Wales and North West England but very rare elsewhere

31st Aug 2019, Whitlinglam, nr. Norwich, Norfolk. Photo: © Carl Reynolds


31st Aug 2019, Whitlinglam, nr. Norwich, Norfolk. Photo: © Carl Reynolds


31st Aug 2019, Whitlinglam, nr. Norwich, Norfolk. Photo: © Carl Reynolds
The rayed form might have some unrayed flowers on it, as this specimen. The outer set of phyllaries surrounding the (here mostly unseen) smaller inner phyllaries, bother of which have many thin longitudinal green stripes and a dirty yellow border. The flower stalk is bent double letting the flower nod downwards.


31st Aug 2019, Whitlinglam, nr. Norwich, Norfolk. Photo: © Carl Reynolds
The striped outer phyllaries, enclosing the disc florets,


31st Aug 2019, Whitlinglam, nr. Norwich, Norfolk. Photo: © Carl Reynolds
This rayed specimen has 11 yellow rays (aka petals) and faces more or less skywards.


31st Aug 2019, Whitlinglam, nr. Norwich, Norfolk. Photo: © Carl Reynolds
Whereas this specimen has but 8 rays.


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) aka 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.


  Bidens cernua  ⇐ Global Aspect ⇒ Asteraceae  

Distribution
 family8Daisy & Dandelion family8Asteraceae
 BSBI maps
genus8Bidens
Bidens
(Bur-Marigolds)

NODDING BUR-MARIGOLD

Bidens cernua

Daisy & Dandelion Family [Asteraceae]

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