by Brian Johnston (Canada)
Helenium is often referred to as
Sneezeweed, since like Goldenrod, it is in bloom at the same
Ragweed, the ‘real’ cause of sneezes. In reality this
was probably applied because in the distant past, its foliage
and powdered to produce ‘snuff’, which was inhaled to cause
It was thought at the time that a sneeze expelled ‘evil spirits’
The genus name Helenium derives from the
word ‘helios’ meaning
sun. The yellow blooms, I suppose, do look vaguely like
species name, probably refers to the yellow, orange and red
pallet of the blooms.
The buds and flowers of this
particular plant were a pleasure to photograph, however the
must be said, was not. Every ‘Mardi Gras’ plant at my
garden centre had a very unpleasant looking blight covering its
leaves. I chose the best of the bunch as a subject for
article, but as you will see, brown spots rear their ugly heads
of the images.
Although the first image in
article, and the three below don’t give the impression that the
is tall – it is! This example is a little over a metre in
with flowers that have a diameter of 5 centimetres.
belong to the Asteraceae family, and what look like flowers are
actually flower-heads composed of a central circular group of
flowers, (disk florets), and an outer ring of larger ray flowers
At an early stage of
the buds are not particularly engaging. Many light green,
pointed sepals surround the growing bud. (The
blight can be seen in both images.)
Later however, the buds become
photogenic, showing a yellowish-brown central disk formed by
disk florets, a ring of light yellow bud-stage ray florets, and
the tips of the light green sepals.
Closer views of this stage
darker brown starfish-like pattern in the central disk.
pattern is formed by the tips of more mature disk floret buds.
As can be seen in the images
follow, not every bud-stage flower-head develops at the same
The structural details at the
of a bud-stage flower-head are certainly worth
flower’s stalk is fluted and its diameter increases near the
base (which in members of this family is referred to as the
‘receptacle’ ). In the last couple of images, it is
the stalk is covered with fine, downy, hairs.
Side views of this same
show the developing ray florets which will eventually open out
the showy, large petals of the flower-head. In the
macro-photographs you can see that these too are covered with
hairs. Unlike those on the stalk, these are coloured.
A view from above shows the
surfaces of these same bud-stage ray florets.
The sequence of images
below, taken with increasing magnification, shows the bud-stage
disk of a flower-head. All of these buds are growing from
previously mentioned ‘receptace’ – a cone-shaped structure with
rounded top which is connected to the stalk. At higher
magnifications, it appears as though the upper surfaces of buds
covered by reddish, shiny, rod-like wires. These
referred to as ‘receptacle chaff’, and they will be discussed in
detail later in the article.
Look at one of the mottled red
yellow petals seen in the image below.
Under the microscope, its
structure is clearly visible. If contrast is increased by
Photoshop’s ‘Levels’ function, the image on the right is the
result. Note that because of the manipulation, the image
An even higher magnification
false-colour image of the cells can be seen below.
At the very edge of a petal
are bulbous-tipped glandular hairs.
More typical, non glandular
cover most of the surface of a ray floret petal.
Higher magnification views of
can be seen below. The first image shows glandular hairs
but not at the edge of a petal.
The image below shows disk
which have begun to bloom.
The uppermost disk flowers in
image have a yellow rod-like structure growing out of what looks
an arrangement of 5 purplish petals. The yellow rod-like
structure is the flower’s immature pistil. Disk flowers near the
red petal are more mature, and their bi-lobed, yellow stigmas
The images that follow give
different views of these structures.
macro-photographs show details of the bi-lobed stigmas.
Under the microscope, the base
the stigma grows out from what looks like a tube with red ridges
top which has pointed red extensions. In the Asteraceae
the anthers are hidden deep within this tube, and as the long
and supporting style extend up through the tube, they brush
anthers, and pick up a coating of pollen. In order to
self-pollination, the two active surfaces of the bi-lobed stigma
tightly sandwiched together during this process. Only
the two lobes of the stigma separate, and become receptive to
pollen. In these photomicrographs, the anthers are hidden
the red-ridged tube, and the style running up through the tube.
For comparison, here is an
which shows an earlier stage in the process, where the flower’s
and supporting style have not grown long enough to push their
out of the tube containing the anthers.
As you can see from the image
the left below, there is no sign of the stigma or style.
right is a photomicrograph showing pollen grains that have
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
erupted from the yellow tubes. Notice the purple hairs
each of the petal tips near the base of the yellow columns.
These ‘hairs’ are referred to
‘receptacle chaff’, and in these photomicrographs they appear
As a Helenium flower ages, the
flowers bloom sequentially from the sides of the dome to its
The first image in the group
shows a flower with only a very few disk florets in bloom.
remainder show what the flower looks like several days later,
almost all of these florets in bloom.
As mentioned earlier, this
flowers are perched at the top of metre high stems. The
are lance-shaped, (lanceolate), and connect directly to the stem
without a stalk. Notice in the closer views that the
circular cross-section stem has longitudinal wings that give it
Some leaves have a ‘swirl’
their connection to the stalk (first and second image),
others do not (third image).
The photomicrograph on the
below shows the cellular structure of one of the leaves, while
the right shows several hairs growing from its lower surface.
Most leaves show evidence of
sort of disease.
Under the microscope, one of
spots is revealed to have ‘walled’ partitions.
Cutting through one of the
stalks reveals that it is hollow and ‘wingless’.
In a treatise entitled Medical
Flora of the United States, written in 1828, the author stated
“sneezeweed could be used in diseases of the head, deafness,
rheumatism or congestion of the head and jaws. The plant
has many other properties, little known as yet and deserving
investigation.” Perhaps – but I rather doubt it.
The low magnification, (to
macro-photographs were taken using a 13 megapixel Canon 5D full
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
lens, the MP-E 65 mm 1:2.8, was used to take the remainder of
The photomicrographs were
using a Leitz SM-Pol microscope (using a dark ground condenser),
the Coolpix 4500.
A Flower Garden of
A complete graphical index of
of my flower articles can be found here.
The Colourful World
A complete graphical index of
of my crystal articles can be found here.
Microscopy UK or their contributors.
Published in the
June 2013 edition of Micscape.
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