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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.

Prunus 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 difference!

A closer view of a couple of flowers shows the irregular edges of petals, and their rather crinkled surfaces.

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 green disk.

Under the microscope, the details of the pollen encrusted yellow anther and white filament can easily be seen.

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!

Photographic Equipment

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.

Reference

Little, Elbert L. National Audubon Society Field Guide to Trees - Eastern Region. 2004. Alfred A. Knopf, Inc. (Chanticleer Press, Inc. New York)

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