Close-up View of a Hybrid
by Brian Johnston (Canada)
Every once in a while, a random genetic
variation occurs in a plant. The term “sport” is used to describe the
result. Seldom does the variation look as spectacular as the one
shown above! Blanket flowers of the wildflower type, (native to
the central United States and Canada), are sometimes called Indian
blankets or Brown-eyed Susans, and they all tend to look like colourful
daisies. For many years hybrid Blanket flowers have been
developed by the horticultural industry, and most share one particular
characteristic of the wildflower varieties. This characteristic
has to do with the outer ray flowers of the flowerhead. In simple
terms, the ray flower petals are flat. In the “sport” Gaillardia grandiflora ‘Fanfare’
however, each outer ray flower petal has a quill, or trumpet
shape. This results in one of the most spectacularly colourful,
and structurally interesting flowers that it has been my pleasure to
Members of the aster family, (Asteraceae), possess a flowerhead
consisting of a central disk, containing small disk flowers, and an outer ring,
containing larger ray flowers.
The genus Gaillardia to which
the particular species photographed for this article belongs, is named
after the French botanist Gaillard de Marentoneau.
The image below shows several
stages in the flowering process. In the central region of the
image, there are several green buds, with an early-stage blooming
flowerhead visible above them. Notice that the ends of the
‘trumpets’ have not yet flared out in this flowerhead. A mature
flowerhead is shown at the bottom of the image.
At least three rings of green
sepals, (modified leaves), completely enclose the early bud-stage
Eventually, the sepals open out to
reveal the tiny, light green buds. At first, (in the image on the
left), there is no way to distinguish between disk and ray flower
buds. A little later however, the outer ring of ray flower buds
differentiates itself (right image). Notice the extreme hairiness
of the sepals shown in both images.
Over a twenty four hour period, the
outer ray flowers have grown in length, and their colours have changed,
The next transformation has the
ends of the closed ray flower tubes starting to open to their final
Side views reveal the overall
cup-shape of a flowerhead at this stage.
Even before their trumpet shaped
ends are fully revealed, ray flowers are strikingly beautiful, with
their deep red vein structure, bright yellow tips, and fine hairy
At last, the ray flowers are
completely in bloom. Strangely, the fused petal tubes of ray
flowers end in variable numbers of petals – four, five, or unusually,
three. Also note that in the central disk of the flowerhead, an
outer ring of disk flowers has begun to bloom.
Below are three additional images
showing Gaillardia grandiflora
‘Fanfare’ ray flowers.
If the lower surface of one of the
sepals, that can be seen in the image on the left, is examined under
the microscope, the stoma and guard cells that control gas transfer
into and out of the surface can be seen.
Higher magnification reveals the
segmented structure of one of the hairs on the sepal’s surface.
The image at right shows the contents of what I assume to an insect egg.
The four images that follow show
the spectacularly colourful structure of Gaillardia grandiflora ‘Fanfare’
The raised, dark red ‘veins’ on the
fused petal section of a ray flower are clearly visible below, as are
the fine hairs that cover its surface.
Ray flower petals are deeply
furrowed, and their surfaces are rough.
A photomicrograph of the upper
surface of a petal can be seen below. Notice the ‘jig-saw-puzzle’
shape of individual surface cells.
A lower magnification view of a
section of the petal near a vein follows.
Veins on the underside of a petal
have red hair-like structures growing from them. These hairs are
also present away from veins, but their number decreases as the
distance from the vein increases.
Higher magnification shows that
these hairs, like those on a sepal, are segmented. (Several
pollen grains can be seen clinging to the petal’s surface in the image
on the right.)
Now let’s turn our attention to the
central disk of the composite flowerhead, with its smaller disk flowers.
Disk flowers bloom first, along the
outer perimeter of the central disk. The pollen coated structures
that project out of the flowers are actually the flower’s
pistils. The pollen generating anthers are hidden from view
within the tiny fused tube of the disk flower, and are not visible to
The strange looking bristly
structures that can be seen below, are the unopened buds of disk
flowers. Each of the tiny red hairs emanating from the top of a
bud is a “pappus”, (a structure connected to a flower’s seed, used to
aid in the transport of the mature seed to a different location,
sometimes by wind, or by attaching to an animal bypasser).
Later, the blooming section of the
central disk has increased in size, and more red pistils are visible.
Notice that it is mostly the ‘newly
erupted’ pistils that are pollen-covered. Those that have been
exposed for some time are almost pollen-free.
The disk flowers shown here have
almost completed blooming. Notice that each red stigma is
With sufficient magnification, the
central disk of Gaillardia
grandiflora ‘Fanfare’ appears to be a cluttered, but
Just above the centre of the image
below, there can be seen a single disk flower with its petals unopened,
but pollen covered. The anthers mentioned earlier are located
just inside these petals. As the stigma and its supporting style
extend out of the top of such a flower, pollen grains become stuck to
the hairs along the edges of the stigmas’s two lobes. Just such a
situation can be seen below the centre of the image. It is just
possible to see the opening at the top of the flower through which the
The two photomicrographs that
follow show the shape of individual disk flower petals (left), and the
spiky edge of the colourless tissue that connects the petals at their
Even with the macro-lens stopped
down to f16, the depth of field is extremely narrow. Examples of
this phenomenon can be seen in the three images below. The first
two show the tiny projections on the edges of stigma lobes that help
capture pollen grains. The last shows the stigma as it is forced
out of the tube formed by the fused disk flower petals. One might
expect self-fertilization to be a problem when the stigma exits from
the disk flower coated with the flower’s own pollen. In fact, it
is likely that the stigma doesn’t become receptive until that original
pollen has fallen off – something that happens quite quickly.
Then, and only then, can a pollen grain transported to the stigma by an
insect, result in fertilization.
On the left below is a
photomicrograph showing the point at which the top of the style becomes
the bottom of the stigma. The cellular structure of the style is
shown in the image at right.
Copious amounts of bright yellow
pollen become trapped by the stigma’s needle-like projections.
A higher magnification reveals the
spiked spherical shape of the pollen grains.
Different illumination techniques
provide alternative views of the grains.
grandiflora ‘Fanfare’ is a perfect example of the superb results
produced by hybridization techniques. However, here, as in many
other human endeavors, chance plays a part. ‘Fanfare’ is not a
hybrid cross of two hybrids. It is the chance “sport” of the
resulting hybrid – something that could not be predicted!
Whatever its origin, ‘Fanfare’
is certainly a stunning flower.
All of the macro-photographs were
taken with an eight megapixel Canon 20D DSLR equipped with a Canon EF
100 mm f 2.8 Macro lens which focuses to 1:1. A Canon 250D
achromatic close-up lens was used to obtain higher magnifications in
The photomicrographs were taken
with a Leitz SM-Pol microscope (using dark-ground and phase-contrast
condensers), and the Coolpix 4500.
A Flower Garden of
A complete graphical index of all
of my flower articles can be found here.
The Colourful World of
A complete graphical index of all
of my crystal articles can be found here.
Microscopy UK or their contributors.
Published in the
October 2008 edition of Micscape.
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