Close up view of an Azalea


A Close-up View of an


Rhododendron x hybrida

by Brian Johnston   (Canada)

The variation in Azaleas available as potted plants, is staggering.  Flower size, shape, form and colour may differ, not only between varieties, but within the same plant, from year to year, if grown in different locations!

Azaleas are members of the genus Rhododendron.  They differentiate themselves from the rest of the Rhododendrons by having one flower per stem.  (This is referred to as having terminal blooms.)  By contrast, the rest of the rhododendrons grow their flowers in clusters.  Even though each Azalea flower has its own stem, there are so many tightly packed stems in a blooming plant, that the flowers may appear to grow in Rhododendron-like clusters.

Horticultural enthusiasts have created hybrid Azaleas for at least two centuries, and this work has created over 10 000 different cultivars.  It’s no wonder that we have the range of choices available today!

The Azalea photographed for this article was chosen in the middle of the Canadian winter, almost at random, from a vast array at my local greenhouse.  No information was supplied about the particular hybrid, and therefore the discussion will simply deal with this as a “typical” example of a cultivar.

Three buds are in the process of opening in the image that follows.  Notice that the sepals (modified leaves) that protect the petals at a very early stage of development have turned brown.  They will fall off before the flowers bloom.

A little later, the tops of the flowers have begun to open.  Several brown sepals can be seen in these images.

Immature leaflets are also protected by the clasping, lighter green sepals that can be seen at the base of each leaflet group.  Notice the long white hairs that grow from each leaflet’s surface.  Even the sepals are hairy.

The white flowers, (2 to 2.5 centimetres in diameter), all have a distinctive pattern of bright red spots on their uppermost petal.  This petal is referred to as the dorsal or upper lobe.  The two petals on either side of the dorsal lobe are called the upper wings.  The two remaining petals are the lower wings.

A view from beneath a group of flowers reveals that each flower is connected to the stem by a short stalk.  The stalks are extremely hairy.  Notice in the image at left, that the bases of the five petals are fused to form a ridged, trumpet-like structure.

This elegant fluted structure can be seen more clearly in the images that follow.

At the very base of the flower, there are five green, hairy, rounded sepals that are collectively called the calyx.

If a section of the dorsal lobe is examined under the microscope, using low power, the central dark area within each bright red spot is revealed.

Higher magnification photomicrographs reveal the fine surface detail on individual surface cells.

Growing out from the fused petal tube are the flower’s reproductive organs.  There is a single green stigma (female pollen accepting organ) which is supported by a lighter green style.  Numerous reddish, bi-lobed anthers (male pollen producing organs) are supported by white filaments.  If you look carefully at the right-hand image, you can see the pollen covered pore at the tip of each of an anther’s lobes.  Pollen exits from these pores.

The two lobes of an anther are clearly visible in the photomicrograph below.

Filaments are covered with translucent hairs.

The three photomicrographs that follow show the pore at the tip of an anther lobe, out of which the irregularly shaped pollen grains exit.

Surface detail on the body of an anther can be seen below.

Notice the pattern on the upper surface of the flower’s stigma.

The dome-shape of the stigma’s tip can be seen in the side view that follows.

Azalea leaves are lance-shaped (lanceolate), and they have a shiny upper surface which is coated with white hairs.

Some hairs grow from the surface away from veins.

Others grow directly from a leaf’s veins.  A second, shorter, (perhaps glandular) type of hair grows randomly over the leaf’s surface.

The azalea studied in this article is of the simplest form, called “single”.  I chose this form because the reproductive structures are not hidden behind voluminous folds of multiple petal layers.  Many other forms exist (with very strange names) such as “hose in hose”, “semi-double”, “semi-double hose in hose”, “double”, “double hose in hose” and “spider”.  Horticulturalists seem to love inventing these names!

Photographic Equipment

All 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 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.

Further Information

Azalea Society of America

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 2010 edition of Micscape.
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