Close-up View of "Chokecherry" Blossoms
by Brian Johnston (Canada)
Common chokecherry shrubs and trees are
a common sight in North America. The small shrub used to obtain
the specimens photographed in this article was found in a woodland area
beside a stream.
virginiana is a member of the Rose Family (Rosaceae).
The genus name Prunus comes
from the Latin prunus, which
refers to a “plum tree”. The species name virginiana refers to the State of
Virginia where the plant is common. If the ripe chokecherries are
eaten, the taste is particularly “puckery” or astringent. This
unpleasant taste accounts for the plant’s common name.
When, in early spring, I brought
the first chokecherry branches home, there was an unpleasant
surprise. Indoors, the twigs and flowers had an extremely
unpleasant smell. At first, I thought that an animal had urinated
on my samples. Experience, and some research, soon led me to the
conclusion that the urine-like odour was given off by the plant
itself. I often keep my wildflower samples on a table (indoors)
for several days while obtaining the images that are required for an
article. In the case of this plant, the smell was so bad that
after the last photograph was taken each day, the branch was removed to
the out-of doors!
Chokecherry buds and flowers grow
at the end of branches in bottlebrush, (or test tube-brush) shaped
clusters called racemes.
When blooming, the flower clusters
are up to 15 cm in length and 2 to 3 cm in diameter. The clusters
below have particularly tightly packed flowers. Notice the finely
saw-toothed elliptical leaves of the plant.
Leaves are 4 to 8 cm long, and 1.5
to 4 cm wide. They are dark green and shiny above, and lighter
green and slightly hairy beneath.
Each flower is about 12 mm in
diameter, and has 5 rounded white petals.
One year earlier, the same small shrub produced much less
tightly packed clusters of flowers. Notice the stark contrast
between clusters produced during the warmest spring and summer on
record in Ontario (above) and
those produced during a very cool, rainy season (below). Climate does make a
A closer view of a couple of
flowers shows the irregular edges of petals, and their rather crinkled
For a period of time after the
petals open, the numerous stamens are still curled and tightly packed
at the flower’s centre.
The two images that follow show the
flower’s reproductive structures. At the centre is the single pistil, consisting of a yellow stigma (female pollen accepting
organ), held aloft by a pale green style.
Numerous stamens grow in a
ring surrounding the pistil. These consist of a yellow anther (male pollen producing
organ), supported by a white filament.
The centre of the flower beneath the pistil is green in colour.
(This is the top of the immature ovary
- the seed producing organ). A brown ring surrounds the central
Under the microscope, the details
of the pollen encrusted yellow anther and white filament can easily be
Another photomicrograph shows the
yellow-green stigma and style.
Chokecherry pollen grains are
roughly ellipsoidal in shape.
Shortly after blooming, the
flower’s petals begin to fall off, leaving the clusters with a
distinctive new appearance. The clusters remain like this for a
month or more as the ovaries develop and increase in size.
If you examine the centres of the
flowers carefully in the images below, you can see that the green disks
(which are the tops of the ovaries), have begun to protrude.
Still later, the developing
ovaries, now darker green in colour, have begun to dominate the
appearance of the clusters.
Eventually, the remnants of the
ring of stamens and the pistil dry up and fall from the flower, leaving
just the developing fruit - the unripe chokecherry “drupe” as it should be called.
(Drupe - A fleshy fruit which usually has a single, large seed.)
Notice in the image of the back of
late stage flowers, the brown “cup” beneath each of the developing
drupes. This is referred to as the hypanthial cup.
The final image in the article should show the deep purple
chokecherry berries in their ripe form. Unfortunately, for two
years in a row, every berry on
the shrubs was eaten by birds while still in the raw, green
state! Rather than cheating, and including an image of berries
from another location, I have decided to let nature make the decision
about the last photograph!
Two-thirds of the photographs in
the article were taken with an eight megapixel Sony CyberShot DSC-F 828
equipped with achromatic close-up lenses (Canon 250D, Nikon 5T, 6T,
Sony VCL-M3358, and shorter focal length achromat) used singly or in
combination. The lenses screw into the 58 mm filter threads of the
camera lens. (These produce a magnification of from 0.5X to 10X
for a 4x6 inch image.) Still higher magnifications were obtained
by using a macro coupler (which has two male threads) to attach a reversed 50 mm focal length f 1.4
Olympus SLR lens to the F 828. (The magnification here is about
14X for a 4x6 inch image.) The remainder of the photographs were taken
with an eight megapixel Canon 20D DSLR equipped with a Canon EF 100 mm
f 2.8 Macro lens. The photomicrographs were taken with a Leitz
SM-Pol microscope (using a dark ground condenser), and the Coolpix 4500.
Little, Elbert L. National
Audubon Society Field Guide to Trees - Eastern Region. 2004.
Alfred A. Knopf, Inc. (Chanticleer Press, Inc. New York)
Microscopy UK or their contributors.
Published in the May
2007 edition of Micscape.
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