A Close-up View of the

Persian Violet

Exacum affine

by Brian Johnston   (Canada)

Persian violet, also called German violet in North America, is native to the island of Socotra, an archipelago in the Indian Ocean.  In Europe, where it is widely cultivated as a house plant, it is referred to as Arabian violet, or Socotran violet, in addition to the names mentioned above.

It is easy to see why the plant is so popular.  Its blue-violet flowers, with prominent yellow stamens, are contrasted against the shiny green leaves.  The long pistil of each flower has a distinctive bend which causes it to lie almost parallel to the petals.  As flowers die, they are constantly replaced by new ones, causing the overall impression of freshness and constancy.

Persian violet buds seem to me to be particularly photogenic, and strangely, have the shape of stubby rocket ships.  At an early stage, they are bright green, matching the leaves, and have five prominent fins.

A little later, the bulbous ‘nose’ of the bud appears white or pale yellow.

After several days, the tightly packed petals forming the ‘nose’ take on a pale violet colour.

In the occasional bud, the packing of petals is particularly three-dimensional.

Most buds however have smoothly packed petals.

Finally, the petals begin to unfurl, revealing five large, bright yellow anthers.

Exacum affine’s mature flowers are 5-merous which means that they possess five petals, five fin-like bracts, and five stamens.  The petals are rounded, and a lime green colour at their bases.  The sturdy lower stalks have very variable lengths, and are reddish-brown in colour.

Closer views of a flower reveal the unusual position of its pistil.  Instead of growing up through the group of stamens, as in a normal flower, it grows parallel to the petals until it is some distance from them.  Only then does it bend to be perpendicular to the plane of the flower.  This adaptation may discourage self-pollination.

Still closer views of the group of  stamens reveal their triangular shape.  It’s not clear whether filaments are absent, or whether the base of each triangle is the filament, and the grooved top section is the anther.

Each anther has two compartments, and is referred to as 2-locular.  Careful examination of the images below reveal the circular opening at the tip (or apex) of each chamber.  It is through these openings that the pollen produced by the anther is released.  The process of pollen release is called dehiscing, and in this species dehiscing occurs through what are referred to as apical pores.  (apical = apex)

A closer view of the two apical pores of an anther can be seen in the photomicrograph that follows.

The flower’s single pistil is composed of a white, sturdy style which supports a pale yellow-green stigma.  At the magnification shown in the two images that follow, the hair-like structures that cover its surface are barely visible.

Under the microscope however the structures are easy to see.  Their function is to increase the surface area of the stigma, and thus increase the chance of pollen capture and retention.  Note that the tip of each ‘hair’ is spherical;  this normally implies a glandular function.

The flower’s ovary is positioned ‘behind’ the petals, and the five fin-like bracts (modified leaves) mentioned earlier grow from its surface.  Notice in the first image the tiny, pointed, green leaflets that point towards the intersection lines of the petals.

If one of the flower’s petals is examined under the microscope, its cellular structure becomes visible.  Note that in order to increase contrast in the photomicrographs, Photoshop’s ‘Levels’ function was utilized.  This causes the image to display false colours.

Near the base of a petal, each cell seems to contain a structure that is bright red.  The ‘Levels’ function was not used here and so the two images are true colour.

While photographing flowers for Micscape articles, I always appreciate plants with sturdy stems and stalks.  These prevent the droopy, vibrating structure syndrome that is the bane of my life.  In order to obtain the illumination that I want, most exposures are in the 1 to 5 second range.  ANY motion of the plant results in out-of-focus or blurry images that are useless.  How I wish that all plants had stems and stalks formed from rigid green concrete!!!!!  I will finish this rant by complementing the Persian violet for its ability to ‘stand still’ while I photograph it.

A branch-point on one of the stems appears to be a marvel of engineering.  Some stalks connect leaves, while others hold flowers.

Leaves in this plant are positioned opposite one another.  Each is glossy green with one prominent central vein, and two subsidiary veins.

Two photomicrographs showing the underside of a leaf can be seen below.  Each of the oval structures is a stoma and its surrounding guard cells.  These control the entry and exit of gases into and out of the interior of the leaf.

A higher magnification photomicrograph follows showing the leaf’s structure near an edge.

If one searches for houseplants in my area, garden centres have very few Persian violets, and very many African violets.  This is a shame, because the plant illustrated in this article is easy to grow and beautiful to look at.


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 December 2013 edition of Micscape.
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