A Close-up View of "Bottlebrush Blazing Star"

Liatris mucronata

by Brian Johnston   (Canada)

This spectacular plant, with its brilliantly coloured flowers, is known as “Liatris”, “Bottlebrush Blazing Star”, “Gayfeather”, or “Narrow-Leaf Gayfeather”, depending upon where you live.  Whatever the name,  these tall plants, which can be up to 1.25 m in height, are certainly impressive. 

A member of the Aster family (Asteraceae), Liatris mucronata doesn’t possess ray florets, although a cursory glance at the flower-head might suggest otherwise.  The long, narrow pink “petals” are in reality, not petals at all, but the flowers’ pistils!  The flower-head contains only disk florets.

The two images that follow show the upper portion of the Liatris stem.  It is interesting to note that most flowers with tall spikes bloom from the bottom up.  This plant blooms from the top down!  The diameter of the flowering tip of the spike is about 3 cm, and in the images, the flowering portion is about 15 cm long.  From the photographs, it is clear that the leaf length diminishes towards the top of the spike.

Each of the leaves immediately beneath the blooming section is about 3 mm wide and 20 mm in length.  A noticeable groove runs the complete length of each leaf.

Under the microscope, this groove appears lighter because of the decreased thickness of the tissue.

Strangely, both the upper, and lower surfaces of the leaf display openings (stoma) through which gas enters the internal structure.  Usually these structures occur only on the underside of the leaf.  Crescent-shaped guard cells control the size of the opening, and therefore the amount of gas transfer.  Notice the interesting wave-like pattern around each stomatal complex in the image on the right.

The “vein” that runs the length of the leaf is actually composed of a number of parallel cellular channels.

Notice the small overlapping red-fringed leaf-like structures that enclose the unopened flower-head.  These are called bracts (modified leaves).  The species name mucronata refers to the shape of these bracts and, translated from the Latin, means “sharp-pointed”.

As the flower-head begins to open, approximately ten disk-flower “buds” become visible.  If you look closely, you can see the pointed red tips of the tiny lobes that form each individual flower’s “petals”.

Since the individual flower-heads are tightly packed on the spike, it is difficult to visualize their structure.  The image on the left below, shows one such flower-head in the bud stage that has been dissected away from the spike.  (Adobe Photoshop was used to remove the needle that supported the structure for the photograph.)  A photomicrograph of the tip of one of the upper bracts is shown in the image on the right.

Viewed from above, the unopened buds of individual disk flowers can be seen.

A little farther up the stem, some of the buds in a flower-head have begun to bloom.  This is extremely difficult to see in the image on the left, but the image on the right provides an alternative view.  (The long pink structures are the pistils of opened flowers.)

Over a period of several days, more and more flower-heads bloom.  The process, as was stated earlier, happens from top to bottom.  However, at any given level in the spike, flowers seem to bloom on one side first.  This process can be seen in the many images that follow.

Eventually, the tip of the spike is covered with fully opened flower-heads.  It is not surprising that the plant was given the name “Bottlebrush Blazing Star”.  At this stage the spike does look like a grotesquely coloured bottle-brush!

A fully blooming flower-head can be seen below. The dark brown structures beneath the ribbon-like pistils are the stamens of the individual flowers.

Even looking at the above photographs, it is difficult to imagine what a single flower looks like.  Here is what one looks like!  The disk floret (or flower) has a corolla with 5 tiny pointed lobes (petals).  At the centre of the flower is a column formed by a number of brown anthers, up through which the two ribbon-like stigmas project.  At the base of the corolla, there are a number of long, hair-like structures, each of which is called a pappus.  These pappi aid in the dispersal of the flower’s seed.

Under the microscope, it is possible to see the cellular structure of the tip of one of the corolla lobes.

The structure of the colourless corolla itself can be seen below.

A higher magnification image of the surface of one of the stigmas (female pollen accepting organs) shows the many spiked ellipsoidal pollen grains on the surface.

The image that follows shows the dark column formed by the multiple anthers (male pollen producing organs) of the flower.

In the two photomicrographs that follow, the two stigmas and styles have been removed to show only the column of anthers.  Notice the interesting fan-shaped structure at the top of each anther in both images.  Also note the pollen grains clinging to the anther’s surface in the image on the right.

The photomicrograph on the left below, shows the cellular structure of one of the ridges on the surface of an anther.  The right-hand image shows the shape of the flower’s pollen.

As mentioned earlier, the corolla of the flower is ringed by pappi.  A photomicrograph of a pappus shows the many hooks that will, with luck, get caught on man or beast, in order to transport the seed to another location after the fertilization of the flower.

The Bottlebrush Blazing Star photographed for this article is a cut-flower obtained at a florist’s shop during the cold Canadian winter.  It provided a welcome visual spectacle for several weeks, contrasting well with the white of the snow outside.

Photographic Equipment

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 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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Published in the September 2009 edition of Micscape.
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