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Bidens cernua

Bidens cernua

Bidens cernua
 
Bidens cernua (Nodding Bur-Marigold, Nodding Beggar-ticks)
Asteraceae (Sunflower Family)

Semi-desert, foothills, montane. Wetlands, disturbed areas, openings. Summer, fall.
Field along Montezuma County Road V, September 1, 2017.

Bidens cernua puts on quite a lovely show in late summer and fall along water courses. Plants are up to several feet tall and flowers are up to 1 1/2 inches in diameter and are numerous. Bidens cernua is an annual wetland loving plant, as the above photographs indicate, and as such it is often in the company of a thicket of other plants, such as the tall, slender Juncus (Rush) plants shown above.

Bidens cernua is a native of North America, Europe, and Asia and it is, as the map below indicates, found widely spread through the United States, including almost all the counties covered in this web site. (Ackerfield's Flora of Colorado incorrectly indicates that Bidens cernua is "Introduced" in Colorado. Innumerable other sources, including the Field Guide to Colorado's Wetland Plants, indicate that it is native.)

Linnaeus named this genus and species in 1753 from European collections made "in Europa ad fontes & fosses", i.e., in Europe from waterways and ditches.

Bidens cernua

Bidens cernua

Bidens cernua (Nodding Bur-Marigold, Nodding Beggar-ticks)
Asteraceae (Sunflower Family)

Semi-desert, foothills, montane. Wetlands, disturbed areas, openings. Summer, fall.
Field along Montezuma County Road V, September 1, 2017.

The leaf-like structures ("bracts" or "phyllaries") that cover the unopened flowers of Asteraceae flowers are typically quite small and green. Flowers of the Bidens genus have two forms of bracts, as the photographs at left show. The outer bracts (bottom red arrow) are long, green, and very leaf-like. The inner bracts (top red arrow) are much shorter, thin, tapering to an acute point, and in the case of the Bidens cernua shown, a transparent smoky gray, at least toward the tip.

Bidens cernua

Bidens cernua

Bidens cernua (Nodding Bur-Marigold, Nodding Beggar-ticks)
Asteraceae (Sunflower Family)

Semi-desert, foothills, montane. Wetlands, disturbed areas, openings. Summer, fall.
Field along Montezuma County Road V, September 1, 2017.

Bidens cernua's floral structure is fascinating. Ray florets may be absent, but they are most often present and number from 6 to 8. They are always sterile. Disk florets are numerous, tubular, and almost always have five, pointed lobes, as the photograph below shows. Rarely there are just four-lobed florets mixed in the same flower head that has almost all five-lobed disk florets.

The photograph below also shows the thin almost translucent, smoky gray bracts ("phyllaries") that are discussed above.

Look at the first photograph at left and you will see a ring of two rows of opened, orange/yellow disk florets surrounding the gray mass of bracts around many unopened ray florets.

In the second photograph at left almost all of the ray florets are opened and only a small area in the center has a gray mass of bracts surrounding unopened disk florets. The outer rows of florets have faded and the bracts are again more obvious.

 

                     Bidens cernua

Bidens cernua

Bidens cernua (Nodding Bur-Marigold, Nodding Beggar-ticks)
Asteraceae (Sunflower Family)

Semi-desert, foothills, montane. Wetlands, disturbed areas, openings. Summer, fall.
Field along Montezuma County Road V, September 1, 2017.

Pappus hairs, the silken structures that we all know from Dandelions, are common on Asteraceae. But pappus may also be awn-like structures as they are on Bidens flowers. In the left photograph below, the bottom arrow points to a disk floret's developing seed. The top arrow points to a barbed pappus awn that will dry as the seed matures and instead of blowing in the wind, this pappus structure will catch on a passing critter and be carried to a new home. Thus Bidens species are often known as "Beggar Ticks".

In the right photograph below, the bottom arrow points to a sterile ray floret seed, the arrow above that points to a barbed awn, the third arrow points to a ray floret fertile seed, the fourth arrow points to the barbed awn on that seed, and the top arrow points to the nearly transparent phyllary (discussed above).

 

                 Bidens cernua      Bidens cernua

Bidens cernua

Bidens cernua

Bidens cernua (Nodding Bur-Marigold, Nodding Beggar-ticks)
Asteraceae (Sunflower Family)

Semi-desert, foothills, montane. Wetlands, disturbed areas, openings. Summer, fall.
Field along Montezuma County Road V, September 1, 2017.

Leaves of Bidens cernua are glabrous, lance-shaped, toothed, and clasp the stem without a petiole.

The specific epithet, "cernua", means "nodding" and was given by Linnaeus because the mature flowers often nod, as shown in two of the flowers that have dropped their ray florets.

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Eradicated
Questionable presence

Bidens cernua

Range map for Bidens cernua