A Close-up View of the Wildflower

"High Mallow"

Malva sylvestris

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 flowers.

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 development.

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 positions.

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 late stage.

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.

Photographic Equipment

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 several images.

The photomicrographs were taken with 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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