A Close-up View of a

Helenium Hybrid

Helenium autumnale 'Mardi Gras'

by Brian Johnston   (Canada)

Helenium is often referred to as Sneezeweed, since like Goldenrod, it is in bloom at the same time as Ragweed, the ‘real’ cause of sneezes.  In reality this appellation was probably applied because in the distant past, its foliage was dried and powdered to produce ‘snuff’, which was inhaled to cause sneezing. It was thought at the time that a sneeze expelled ‘evil spirits’ from the body!

The genus name Helenium derives from the Greek word ‘helios’ meaning sun.  The yellow blooms, I suppose, do look vaguely like suns.  Autumnale, the species name, probably refers to the yellow, orange and red colour pallet of the blooms.

The buds and flowers of this particular plant were a pleasure to photograph, however the foliage, it must be said, was not.  Every ‘Mardi Gras’ plant at my local garden centre had a very unpleasant looking blight covering its leaves.  I chose the best of the bunch as a subject for this article, but as you will see, brown spots rear their ugly heads in many of the images.

Although the first image in the article, and the three below don’t give the impression that the plant is tall – it is!  This example is a little over a metre in height, with flowers that have a diameter of 5 centimetres.  Heleniums belong to the Asteraceae family, and what look like flowers are actually flower-heads composed of a central circular group of disk flowers, (disk florets), and an outer ring of larger ray flowers (ray florets).

At an early stage of development, the buds are not particularly engaging.  Many light green, narrow, pointed sepals surround the growing bud.  (The aforementioned blight can be seen in both images.)

Later however, the buds become more photogenic, showing a yellowish-brown central disk formed by bud-stage disk florets, a ring of light yellow bud-stage ray florets, and finally the tips of the light green sepals.

Closer views of this stage show a darker brown starfish-like pattern in the central disk.  The pattern is formed by the tips of more mature disk floret buds.

As can be seen in the images that follow, not every bud-stage flower-head develops at the same rate.

The structural details at the back of a bud-stage flower-head are certainly worth investigating.  The flower’s stalk is fluted and its diameter increases near the flower’s base (which in members of this family is referred to as the ‘receptacle’ ).  In the last couple of images, it is apparent that the stalk is covered with fine, downy, hairs.

Side views of this same flower-head show the developing ray florets which will eventually open out to be the showy, large petals of the flower-head.  In the macro-photographs you can see that these too are covered with short hairs.  Unlike those on the stalk, these are coloured.

A view from above shows the top surfaces of these same bud-stage ray florets.

 The sequence of images shown below, taken with increasing magnification, shows the bud-stage central disk of a flower-head.  All of these buds are growing from the previously mentioned ‘receptace’ – a cone-shaped structure with a rounded top which is connected to the stalk.  At higher magnifications, it appears as though the upper surfaces of buds are covered by reddish, shiny, rod-like wires.  These structures are referred to as ‘receptacle chaff’, and they will be discussed in more detail later in the article.

Look at one of the mottled red and yellow petals seen in the image below.

Under the microscope, its cellular structure is clearly visible.  If contrast is increased by using Photoshop’s ‘Levels’ function, the image on the right is the result.  Note that because of the manipulation, the image is false-colour.

An even higher magnification false-colour image of the cells can be seen below.

At the very edge of a petal there are bulbous-tipped glandular hairs.

More typical, non glandular hairs cover most of the surface of a ray floret petal.

Higher magnification views of hairs can be seen below.  The first image shows glandular hairs near, but not at the edge of a petal.

The image below shows disk florets which have begun to bloom.

The uppermost disk flowers in each image have a yellow rod-like structure growing out of what looks like an arrangement of 5 purplish petals.  The yellow rod-like structure is the flower’s immature pistil. Disk flowers near the large red petal are more mature, and their bi-lobed, yellow stigmas are visible.

The images that follow give different views of these structures.

High magnification macro-photographs show details of the bi-lobed stigmas.

Under the microscope, the base of the stigma grows out from what looks like a tube with red ridges and a top which has pointed red extensions.  In the Asteraceae family, the anthers are hidden deep within this tube, and as the long stigma, and supporting style extend up through the tube, they brush against the anthers, and pick up a coating of pollen.  In order to discourage self-pollination, the two active surfaces of the bi-lobed stigma are tightly sandwiched together during this process.  Only later do the two lobes of the stigma separate, and become receptive to pollen.  In these photomicrographs, the anthers are hidden between the red-ridged tube, and the style running up through the tube.

For comparison, here is an image which shows an earlier stage in the process, where the flower’s stigma and supporting style have not grown long enough to push their way up out of the tube containing the anthers.

As you can see from the image on the left below, there is no sign of the stigma or style.  On the right is a photomicrograph showing pollen grains that have escaped from the open end of the tube seen in the image at left.

This image shows the two stages.  In the lower part of the image, the stigma and style have erupted from the yellow tubes.  Notice the purple hairs that cover each of the petal tips near the base of the yellow columns.

These ‘hairs’ are referred to a ‘receptacle chaff’, and in these photomicrographs they appear glandular in nature.

As a Helenium flower ages, the disk flowers bloom sequentially from the sides of the dome to its top.

The first image in the group below shows a flower with only a very few disk florets in bloom.  The remainder show what the flower looks like several days later, with almost all of these florets in bloom.

As mentioned earlier, this plant’s flowers are perched at the top of metre high stems.  The leaves are lance-shaped, (lanceolate), and connect directly to the stem without a stalk.  Notice in the closer views that the nearly circular cross-section stem has longitudinal wings that give it a very unusual appearance.

Some leaves have a ‘swirl’ near their connection to the stalk (first and second image),  while others do not (third image).

The photomicrograph on the left below shows the cellular structure of one of the leaves, while that on the right shows several hairs growing from its lower surface.

Most leaves show evidence of some sort of disease.

Under the microscope, one of the spots is revealed to have ‘walled’ partitions.

Cutting through one of the flower stalks reveals that it is hollow and ‘wingless’.

In a treatise entitled Medical Flora of the United States, written in 1828, the author stated that “sneezeweed could be used in diseases of the head, deafness, headache, rheumatism or congestion of the head and jaws.  The plant probably has many other properties, little known as yet and deserving investigation.”  Perhaps – but I rather doubt it.

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.

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Published in the June 2013 edition of Micscape.
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