Close-up View of Four Beggar-Ticks:
(Bidens frondosus, Bidens vulgatus, Bidens
tripartitus & Bidens cernuus)
in the summer, several interesting species of wildflowers called “Beggar-Ticks” bloom along the edge
of a stream near my home. All are members of the Aster family,
whose flowers normally consist of both inner “disk” florets and outer
“ray” florets. The beggar-ticks however, are somewhat unique in
that some have ray florets, some have a variable number of stunted ray
florets, and some have only disk florets!
The strange name of the group, “Beggar-Ticks”, is related to the double-barbed seed which easily sticks to the pants of beggars, (and others), who come into close contact with the plant in the fall. In fact the genus name Bidens comes from the Latin bis, meaning "twice", and dens, meaning "tooth", referring to the two barbs on each seed.
Devil’s Beggar-Ticks - Bidens frondosus
Along the edge of the previously mentioned stream, this is by far the most common Bidens species. Most plants grow to about 80 cm in height and have many yellow-orange blooms. A typical example is shown as the first image in the article. Each flower-head tends to be from 1.0 to 1.5 centimetres in diameter.
A closer look at a bloom reveals the disk-like head containing many individual flowers, and the surrounding tiny leaflets called “phyllaries”. Devil’s Beggar-Ticks have ten or fewer of these phyllaries.
Each of the orange disk flowers has five petals. Notice that the flower closest to the viewer is on the end of a short rod-like stalk which grows out of a pale green structure. This is the ovary containing the ovule that will develop eventually into a seed. The two pale green spikes framing the flower are the immature spiny bristles that will eventually help carry the seed to a new location stuck to the beggar’s pants!
The image below shows the flowers from above, with their almost black stamens and pistils.
Surrounding the outer edge of each flower-head is a double row of phyllaries, (modified leaves), that are quite different than the ones mentioned earlier. These are broader, much shorter, and finely striped in purplish-black.
Under the microscope it is possible to see details that cannot be resolved by macrophotography. The following two images show the developing backward pointing spikes on the immature bristles attached to the ovary.
A photomicrograph of a single flower reveals the component parts. Projecting out from the tiny petals is a large diameter tube formed by the five fused stamens, three of which can be distinguished in the photomicrograph. At the top of each is an enlargement, the anther (male, pollen producing organ). Projecting out of this larger tube is the narrower style, holding at its tip, the stigma (female, pollen accepting organ). In the image, both anthers and stigma are encrusted with pollen.
Below, on the left, two yellow spiked pollen grains can be seen adhering to the surface of one of the striped phyllaries mentioned earlier. The image on the right shows a group of pollen grains attached to the edge of a phyllary.
The tip of one of these phyllaries is shown on the left. Note that it is covered with tiny transparent, hair-like projections. The higher magnification image of one of these hairs reveals that it is segmented.
In early fall, the entire plant takes on an attractive coppery colour. The image below left shows three younger flower-heads and an older one that has opened up into a late stage seed-head. On the right is a higher magnification image of the former. The photograph clearly shows the outer ring of leaflet-like phyllaries, the inner rings of striped phyllaries, and the maturing seeds.
In the last stage of development, the now mature fruit, seeds called achenes, open out into an almost globular shape. This configuration puts the spiked barbs on the outer surface of an imaginary sphere, and provides them maximum access to any passing ambulatory transporter.
The seed of a Beggar-Tick may not be beautiful, but I can attest from personal experience that it is very efficient. Considerable force is required to remove one from a sock or pant leg. Even shoe-laces are not immune! (Although it may look like the seed below is hanging in mid-air, it is actually suspended from the tip of a spiked phyllary by a single spider’s thread!)
Tall Beggar-Ticks - Bidens vulgatus
This species grows side-by-side with Devil’s Beggar-Ticks. It is similar, but has many more of the outer leaflet-like phyllaries which are arranged in a whorl around the disk flowers.
Three-Parted Beggar-Ticks - Bidens tripartitus
This species also grows intermixed with the others along the stream edge. The main difference from the previous species is that it has very tiny yellow ray florets. Strangely, the number of these florets is extremely variable, and I didn’t find a single example with a full set!
Nodding Beggar-Ticks - Bidens cernuus
The image below shows how different this species appears, with its long, narrow leaves and attractive yellow petals. When mature, the flowers tend to droop slightly, as in the photograph, and this is why the common name was chosen to be “nodding”.
A closer view reveals the distinguishing characteristics of the species, six to eight yellow ray florets surrounding a yellowish-brown disk. The outer phyllaries are similar to those of Devil’s Beggar-Ticks’.
A higher magnification shows that the inner phyllaries, just inside the petals, are also pale green with dark stripes.
In fact, in this species, the striped phyllary rings extend right to the centre of the flower-head, and in an immature bloom, form the central dark area. (The stripes can be seen clearly in the photograph.) Surrounding this central area, yellow stigmas can be seen projecting from the flowers.
A side view shows additional details, including a couple of spider’s-web threads that are commonly found on the flowers.
Two photomicrographs of an immature flower are shown below. At this stage the tube of fused stamens is visible, each topped by an anther, but the style has not yet grown out of the end of the tube.
final image shows that the pollen grains of this species look
identical to those of the “devil’s” flower.
The identification of the various Beggar-Ticks species was extremely difficult. There seems to be little information about the plant available on the Web or in reference texts. My identifications were based upon the information in the first of the references listed below. (The others seem to have little or no mention of these species!)
The photographs in the article were taken with an eight megapixel Sony CyberShot DSC-F 828 equipped with achromatic close-up lenses (Nikon 5T, 6T, Sony VCL-M3358, and shorter focal length achromat) used singly or in combination. The lenses screw into the 58 mm filter threads of the camera lens. (These produce a magnification of from 0.5X to 10X for a 4x6 inch image.) Still higher magnifications were obtained by using a macro coupler (which has two male threads) to attach a reversed 50 mm focal length f 1.4 Olympus SLR lens to the F 828. (The magnification here is about 14X for a 4x6 inch image.) The photomicrographs were taken with a Leitz SM-Pol microscope (using a dark ground condenser), and the Coolpix 4500.
The following references have been found to be valuable in the identification of wildflowers, and they are also a good source of information about them.
Published in the August
2005 edition of Micscape.
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