Close-up View of the Wildflower
by Brian Johnston (Canada)
Ubiquitous Malva neglecta, the first mallow
studied this month, is sometimes referred to as the ‘dwarf mallow’ due
to its diminutive size. By comparison, this mallow is a giant,
sometimes growing to 0.5 metres or more in height. While neglecta tends to hug the ground as
it grows, sylvestris
possesses strong upright stems that support striking, dark pink, veined
Although mallows originated in
southern Europe and Asia, they have now spread worldwide as
weeds. Malva neglecta
is extremely common in south western Ontario where I live; sylvestris on the other hand is
quite rare. The example photographed in this article was found
growing under an old wooden fence at the edge of an abandoned
field. Its brilliant colouration made it easy to pick out amongst
the surrounding green weeds.
As can be seen in the image that
follows, each flower has five heart-shaped petals that are pink in
colour. Numerous dark red, radial stripes reach almost to the
petal’s upper edge. (Notice that the petals do not
overlap.) The plant’s leaves are heart-shaped, or kidney-shaped,
and possess 3 to 7, (in this case 5), rounded, toothed lobes.
The growing tip of a stem can be
seen below. Note the very small buds in various stages of
A cluster of buds also grows from
each leaf axil, (the point of connection of leaf stalk to the main
stem). Two examples of these clusters are shown below.
Each unopened bud is ringed by
green leaflets. The five sepals, (modified leaves) that enclose
the flower’s petals, are joined at their edges in the unopened bud,
forming distinct ridges.
As the bud grows, the sepals are
pushed apart at the top, revealing the deep purple petals packed
beneath. Notice the intense hairiness of both the encircling
leaflets, and the sepals.
Strangely, the occasional bud shows
petals with a much lighter pink colouration.
Eventually, the flower’s petals
begin to open, revealing the reproductive structures at its
centre. If you look carefully at the image on the right, you
should be able to distinguish both the smaller leaflets, and larger
sepals that ring the base of the flower.
If a darker vein on a petal’s
surface is examined under the microscope, the elongated, pigmented
cells that form the outer epithelial layer are visible.
By contrast, the cells in the
lighter coloured areas surrounding the veins are composed of what look
like strings of roughly spherical cells. The low magnification
image on the right shows both types of cells for comparison.
At the centre of each flower, there
is a tube from which numerous stamens grow. This tube encloses
the style. When the flower first opens, pollen grains are so
numerous that they obscure the anthers, and the flower’s stigma. A dusting of pollen can be seen clinging
to each petal’s surface.
At the centre of each pollen
cluster, there appears to be a dark-coloured structure.
Under the microscope, this
structure reveals itself to be the unusually shaped anther, (male
pollen producing organ). Notice the turned-up ends and
distinctive raised, white collar that bisects the top of the
anther. The filament that supports the anther can be seen in the
image on the left.
Mallow pollen grains are perfectly
spherical, and are covered with short spikes. Since the depth of
field at this magnification is very small, the images that follow
attempt to show detail in various planes.
Here the pollen has been removed
from the anthers, and the branching structure of the many stamens
emanating from the central tube is revealed. Notice that this
tube extends beyond the top-most stamens.
The tip of the multi-lobed stigma,
(female pollen accepting organ) can just be seen protruding from the
top of this central tube in the image that follows. Note the
spherical pollen grains adhering to the ends of the lobes.
Eventually the style grows long
enough to permit the radial lobes of the stigma to take up their final
Photomicrographs showing a stigma
lobe can be seen below. Notice the many fine hairs that are
concentrated in a band along the lobe’s length. The third image
gives a good idea of the scale of pollen grains compared to a lobe.
The characteristic fruit of the
mallow consists of a flat, circular capsule which contains many
one-seeded sections. The five sepals remain, as does the stub of
the reproductive tube.
In another fruit, the sepals are in
a more horizontal position. Note in the image on the right, that
the small ring of leaflets below the sepals, is still present at this
It is interesting to compare the
light green, partially opened mallow leaf seen on the left below, with
the darker green mature leaf on the right.
Although there are superficial
differences between the two mallow species studied this month, their
similarities are striking.
Most 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 few were taken
using a Sony DSC F-828 eight megapixel camera. 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 a dark ground condenser), and the
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 2010 edition of Micscape.
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