One look at this striking plant was enough to convince me that it should be the subject of one of my Micscape articles. Its spectacularly shaped, and intensely colourful blooms made nearby plants in the garden centre look positively drab!

The original plant that was used to produce this cultivar is the Eastern purple coneflower which is native to the central and south-eastern regions of the United States.  It is a member of the Aster family (Asteraceae), and thus possesses flower-heads composed of outer ray flowers and inner disk flowers.  In addition to its use as an ornamental, it is popular for its (possible) medicinal properties.

The bud stage of the cultivar ‘Pink Double Delight’ can be seen below.  At this early stage there is little evidence of the final colouration of the bloom.


A little later however, the curled protrusions that will eventually become the flower-head’s ray flowers have begun to have a faint pink colouration. The central disk, composed of disk flowers, has not begun to bloom.



Notice the whorls of curved green bracts (modified leaves) that form the base of the flower-head.


Note in the images that follow, that both the edges of the bracts, and the surface of  the supporting stalk are covered with fine colourless hairs.



The length of the folded or rolled ray florets increases by millimetres per day as the flower-head matures.


A view from above of a bud flower-head shows the ring of lengthening ray flower petals, and what look like the tips of immature disk flower buds.  In fact, the central structures are not buds at all!


Side views of a bud stage flower-head, which has been cut longitudinally in order to view the internal structures, can be seen below.  In the images, the shorter, pale green structures with grooved tips are the unopened disk flowers, while the longer, darker green structures with reddish tips are referred to as ‘receptacle chaff’.  These rod-like structures surround the many disk flower buds, and in this genus, are the same length or longer than the buds.  The genus name Echinacea derives from the Greek echinos (hedgehog) and it refers to this array of spike-like structures growing from the flower-head’s base (or receptacle).


As usual, looking at the bud stage of this plant provides few clues to the simply magnificent inflorescence that it will transform into.  Notice that in this cultivar, the ratio of ray flowers to disk flowers has a very small value.  The flower-head blooms from the outside in.




Views from the back of an inflorescence show the whorls of bracts that ‘cup’ its base (or receptacle).  Notice that near the whorl of bracts, the stalk increases in diameter and has a group of longitudinal groves on its surface.  Also note the very three-dimensional, longitudinal veining on the underside of the ray flower petals.




Ray flower petals are flat, and have a variable number of pointed lobes at their tips.  Disk flowers have tubular corollas with a variable number of pointed lobes along their top edge.


Closer views of the tips of ray flowers can be seen below.


A similar view of the tip of a disk flower follows.


If one of these petals is examined under a microscope, its cellular structure and colouration become easier to see.


Higher magnification reveals more details.  Notice that the two images that follow show exactly the same view of a petal.  The enhanced contrast in the second image is the result of using Photoshop’s ‘Levels’ function.  Because of this the second image is not true colour.


Photomicrographs (again using the ‘Levels’ function) reveal some of the structures on the underside of a ray petal.


The outer ray flowers of this species have very large, relatively flat petals.  Disk flowers however, possess a tubular corolla with pointed lobes around its upper edge.  The closer the flowers are to the centre of the disk, the smaller they are.


Although the receptacle chaff mentioned earlier start out longer that the disk flower buds, the blooming disk flowers are tall enough to hide them from view.  Only in the centre of the disk are they still visible.


Here are several closer views of the interface between bud-stage, and blooming, disk flowers.  Remember that the receptacle chaff have bright red tips, while the bud-stage flowers have pale green tips.



Here is a photomicrograph that shows the tip of a disk flower bud.  Its mixture of red and green indicates that it is about to bloom.


If one of the bud’s petals is removed and examined under the microscope, the colouration of individual cells becomes visible.


Deep with the corolla tube of a disk flower this strange looking structure exists.


Higher magnification photomicrographs reveal that it is the flower’s pistil.  On the surface of the stigma, an array of variable length rod-like hairs help capture and retain pollen grains.



During the period of time that I photographed this plant, the flowers’ pistils did not grow to such a length that they were visible to a casual viewer.


The base of the flower-head, from which both ray and disk flowers grow is called the receptacle.  In this species it has a dome shape. One central view showing only buds and chaff, and one side view showing blooming disk flowers can be seen below.  Notice that the base of the blooming flowers has a bright red colour which abruptly changes to pure white farther down.


Two images show views of an immature bud with its monochrome colouration, and the third shows an older bud which is taller, and has a faint pink colouration near its tip.



Notice how much taller the blooming disk flowers are compared  to the receptacle chaff.  The red swelling at the base of the corolla tube is the flower’s ovary.


Additional views of the interior of the coneflower inflorescence are shown below.  Even the interior of a flower is attractive when viewed up-close!




The upper surfaces of the plant’s leaves have a small number of prominent longitudinal veins and a multitude of seemingly random fine veins.  Fine hairs grow all over the upper surfaces.  Botanists describe the shape of the leaves as broadly lanceolate.


The lower surface of a leaf has fine hairs as well, and its veining is easier to see.



Photomicrographs of the lower surface reveal these hairs, and in the third image, the stomata and guard cells that control gas entry into and out of the leaf are visible.



Medical benefits of Echinacea have been claimed for many years.  It is interesting to note that back in 1852 the starter plant of this cultivar, Echinacea purpurea, was put in the official United States Dispensary claiming that it was useful in the treatment of syphilis.  It is well to remember however that it was also believed to cure snakebites, colds, mumps, wounds, burns etc.  Need I say more?


Photographic Equipment

The low magnification, (to 1:1), macro-photographs were taken using a 13 megapixel Canon 5D full frame DSLR, using a Canon EF 180 mm 1:3.5 L Macro lens.

A 10 megapixel Canon 40D DSLR, equipped with a specialized high magnification (1x to 5x) Canon macro lens, the MP-E 65 mm 1:2.8, was used to take the remainder of the images.

The photomicrographs were taken using a Leitz SM-Pol microscope (using a dark ground condenser), and the Coolpix 4500.



A Flower Garden of Macroscopic Delights

A complete graphical index of all of my flower articles can be found here.


The Colourful World of Chemical Crystals

A complete graphical index of all of my crystal articles can be found here.

 All comments to the author Brian Johnston are welcomed.