Close up view of an Azalea
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.
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
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
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
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
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
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!
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.
Azalea Society of America
A Flower Garden of
A complete graphical index of all
of my flower articles can be found here.
The Colourful World of
A complete graphical index of all
of my crystal articles can be found here.
Microscopy UK or their contributors.
Published in the
December 2010 edition of Micscape.
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