A close-up view of Edelweiss


A Close-up View of Edelweiss

Leontopodium alpinum

by Brian Johnston   (Canada)

Many people know of the Edelweiss from the popular song composed by Rogers and Hammerstein for their stage play “The Sound of Music”, which was later transformed into an even more popular movie by the same name.  Unfortunately, the song gives the impression that the plant possesses snowy white blossoms, something that is clearly not correct.  In fact, the silvery-white, wooly ‘petals’, with tinges of green, are not petals at all, but modified leaves called bracts.  The true flowers are small, inconspicuous, and located at the centre of the rosette of bracts.

The plant’s common name derives from the German edel, which translates to noble, and weiss, meaning white.  Its genus name Leontopodium derives from the Greek leon meaning lion, and podion, which was the diminutive of pous, meaning foot – hence lion’s paw.  The furry rosette of bracts that frame the flower-head could, I suppose, be thought to resemble this structure.

Edelweiss, a member of the Asteraceae family, is native to Europe and the Alps.  Its deep roots protect it from the high winds and drought that are common in the extremes of climate found at altitudes from 1700 to 2700 metres where it grows.

An immature flower-head can be seen in the image below.  At this early stage there is almost no hint of the flowers that will eventually bloom at its centre.

Closer views of one of the hairy bracts reveal the longitudinal groove that runs most of their length.  In the upper right corner of the first image, several pollen covered reproductive structures, poking through the wooly hairs, indicate the location of flowers.  These white hairs are believed to protect the flower-head from the high ultra-violet radiation levels found at the altitudes where the plant grows. 

Photomicrographs showing these UV absorbing hairs can be seen below.  They form a tangled mat over the bract’s surface.

The underside of a bract has a smaller number of hairs growing from its surface, and the central vein is extremely prominent here.

Two views of the potted plant used in this article can be seen below.  The stems grow to about 20 centimetres in height, and most flower-heads have a diameter of about 4 centimetres.

It is interesting to note that many of the leaves of the plant are not protected by wooly hairs.  Perhaps the mass of flower-heads above, shades the leaves from most of the damaging UV radiation.

Notice in the rosette of bracts that frame the flower cluster at its centre, that the density of white hairs increases towards the centre.  Also note that a few Edelweiss flowers have started to bloom in each flower-head.

Close examination of the image on the right below will reveal several blooming flowers, each with a corolla composed of five, pointed, off-white petals, and a prominent columnar pistil coated with bright yellow pollen grains..

Side views of a flower-head and its supporting stem reveal additional information.  The leaves beneath the flower-head are directly connected to the stem without a stalk (clasping).  In the image on the left, the yellow pistils can be seen to project out of the flowers a distance greater than the diameter of the flower itself.

The sequence of images that follows reveals that the flowers bloom first in a ring at the base of the rosette of bracts.  Flowers near the flower-head's centre bloom up to a week later.  The hair density at the centre can be so great that only the pistil is able to force its way through the matted hairs to become visible to an observer.

At the magnifications used in the images that follow, it is possible to distinguish a flower’s five petals and pistil.

Some flower-heads have considerably smaller central areas than others.  The one shown on the right appears featureless, but later, additional flowers will appear in this area.

Side views of a flower-head reveal the many pollen covered pistils that project out of the central area.

Now let’s take an even closer look at Edelweiss flowers.  As in many other members of the Asteraceae family, the anthers of a flower are concealed within a column up through which the style pushes the stigma.  As the stigma comes in contact with the pollen covered anthers, pollen grains adhere to the stigma and are carried with it.  In the sequence of images that follows, notice that so many pollen grains coat the stigma that it is difficult to differentiate it from the column itself.  In several flowers however, its slightly smaller diameter, and lighter colour help to distinguish it from the column.

This is particularly true in the flower closest to the observer in the image below.  Only the very tip of the stigma is visible in the flower at the centre of the image.

Now for a surprise!  So far you may have concluded that a flower-head contains only one central disk of flowers.  The reason is simple;  usually only one of the five to ten disks is visible when the head begins to bloom.  Almost as if by magic, the others begin to appear over a period of several days to a week.

In many cases only the yellow pistils are apparent, poking through the thick mat of white hairs.

Eventually flower disks appear in the most unlikely places, such as the intersection point of two bracts (upper right corner of the three images that follow).

Usually the central flower disk is the most mature.

Sometimes however, the central disk is the ‘baby’ of the bunch.

As I mentioned earlier, flower disks can occur in the most unlikely of places.  The one shown below appears to grow directly from the side of the stem!

When a flower disk has completed blooming, the flowers turn a brown colour, and their structures begin to disintegrate.

Flower disks adjacent to the older disks are often in full bloom.

The three images that follow show a mystery that I have been unable to resolve.  If you examine them, you will see a number of thread-like structures with bifurcated tips emerging from the mat of hairs.  They look very much like ‘typical’ flower stigmas atop their supporting styles – but they can’t be since members of the Asteraceae family don’t have pistils that look like this!  What could they be?

If a section of an Edelweiss flower disk is examined under the microscope, the flowers’ corollas are surrounded by many almost transparent, lobed, thread-like structures.  The petals seen in the images are immature, and green in colour.

Instead of each flower’s base possessing a whorl of modified leaflets called the calyx, here the calyx consists of long, multi-forked transparent hairs.

In the image below, a clump of Edelweiss pollen grains has glued itself to the tip of one of the hairs.

The photomicrograph on the left below shows a single flower before the column containing stamens and pistil has appeared.  On the right is a slightly older flower in which the petals have opened out into their final position.

A higher magnification reveals the cellular structure of one of the petals.

In the two images below, the column containing the flower’s anthers has projected up beyond the corolla.  As yet however, the pistil has not extended out of the column.

The following images show the lobed top of the column, and the pollen covered pistil that has finally protruded far enough to be visible.

As is the case with most stigmas, this one has projections at its tip that help to acquire and retain pollen grains.

Edelweiss is termed a ‘short-lived’ perennial since if its flower-heads are picked from the plant over a number of growing seasons, it becomes unable to propagate by seeding.  For this reason the plant is protected in many countries, most notably Austria.

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.

An 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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