A Close-up View of the Wildflower
"Plains Coreopsis"

(Coreopsis tinctoria)

by Brian Johnston   (Canada)

This very colourful wildflower is not common in my vicinity.  The only small patch that I have come across grows in the partial shade, beside a small stream that commonly overflows its banks during heavy rains.  Although all of these Coreopsis plants grow in an area less than four square metres, there is amazing diversity in the appearance of the flowers.  Blooms may be yellow, red, purple or a combination of these colours.

Plains Coreopsis belongs to the Aster family whose members possess composite flower-heads,  usually containing both ray and disk flowers.  The blooms of this wildflower bear some resemblance to those of another member of the family, the daisy.  Each flower head has a diameter of from two to four centimetres.

The genus name Coreopsis comes from the Greek for “bug”, and refers to the plants’ seeds which when dried are flat and resemble the same.  The species name tinctoria refers to the colourful appearance of the blooms, and is given to plants involved in staining or dyeing processes.
Most plants near the stream grow to about 40 centimetres in height and possess very fragile looking, but actually amazingly strong stems.  Plants bloom until the beginning of October in Southern Ontario.

The ray flowers (petals), of which there are usually eight, are sometimes bent backwards slightly, as in the first image in the article, or forwards as in the image below.

Notice the small diameter of the stems compared to that of the flower-heads.  An unopened bud can be seen in the upper left corner of the image.

At this early stage of development, the bud is protected by an outer sheath of specialized leaves called phyllaries.  They can be seen to be light green with brown edges.

Later, as the bud begins to open, these phyllaries have turned a deep purple-brown colour.  Notice the darker veins in the unfurling yellow petals.

Some Plains Coreopsis plants’ ray flowers have a much larger purple area than others.  Compare the two images below with the first image in the article to see the difference.

The view of the back of a flower-head is interesting.  The series of modified leaves (phyllaries) beneath, (or behind) the flowers is called the involucre.  In this species, the involucre is said to be dimorphic because there are two forms of phyllary present.  The outer series is composed of eight short green phyllaries, while the inner series has eight larger reddish-green, finely striped phyllaries.

Once the flower-head has completely opened up, the outer ray flowers begin to bloom first.  The central area of unopened disk flowers appears dark purple.

A little later, the outermost disk flowers begin to bloom.  I am always amused by the intricate terminology that “experts” use to describe a scientific phenomenon in order to keep “amateurs” in awe of their expertise.  One nameless reference describes Coreopsis disk flowers as having a

“Disk to 8mm broad, subglobose. Corolla tube to 3mm long, yellow-orange, deep purple at apex, 4-lobed, fertile. Style bifurcate, orange at apex, exserted. Achene 1.8mm long in flower, flattened, glabrous. Pappus absent or a minute crown.”

What?!  (I shouldn’t really complain, since my area, chemistry, uses at least, if not more complex terminology.  Could you write the structural formula for 1,2-dichloro-3-methyl-5-ethyl benzene?  Enough said!  If things were explained simply, teachers like me would be less necessary.  Horror of horrors!!)

Notice that each disk flower in the image below has a tiny yellowish tube that opens up to form a narrow ring of four purple petals that are fused together, and thus difficult to distinguish.  A tube formed by fused anthers projects out of each flower.

Eventually, all of the disk flowers open, and the mature composite flower-head is revealed.

There seems to be a gradual opening up of the ends of the fused anthers, revealing more pollen at each stage.

If one of the disk flowers is carefully removed from a flower-head like the one below,

and  a microscope is used to magnify the top of the flower, it looks like this.   Copious amounts of spherical yellow pollen collects at the top of the anthers (male, pollen producing structures).

The details in the tiny tip of one of the disk flower petals can be seen in the following image.

In the image below, on the left, several stigmas (female, pollen accepting structures) can be seen.  The more highly magnified image of some stigmas, on the right, reveals that they have two curled lobes.

Another image showing these bi-lobed stigmas follows.  The ray florets have been removed to show the detail in one of the inner phyllaries.

Under the microscope a stigma is an attractive orange-yellow colour, and pollen grains are visible on its surface.

The bi-lobed stigma is held aloft by the style, a column that has randomly located red spots on its component cells.

As the style ages, it becomes darker red, and the surface becomes rougher.

Earlier in the article, I mentioned the diversity in the colour of blooms of Plains Coreopsis.  In addition to the two colourations shown earlier, some blooms are mostly red but speckled with yellow.

Some are almost completely red.

Others have no red at all outside of the central disk.

Plains Coreopsis is such an attractive wildflower that it is sometimes used for landscape beautification along roadsides, and even in gardens.  Occasionally, the plant proliferates to such an extent that it is considered a noxious weed.  Where I live, the climate is harsh enough to prevent such abundance, and finding these colourful blooms is simply a pleasant happenstance!

Photographic Equipment

The photographs in the article were taken with an eight megapixel Sony CyberShot DSC-F828 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 f1.4 Olympus SLR lens to the F828.  (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.

 All comments to the author Brian Johnston are welcomed.

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