Close-up View of the Wildflower "Sweet Pea"
by Brian Johnston (Canada)
the last few years, I have systematically searched for wildflowers in
the vicinity of my home. Many species are ubiquitous. What
surprises me is the number that grow in only one location. I
often wonder what strange phenomenon led to their occurrence in a
particular spot. The sweet pea plants studied in this article
grow in an area less than one square metre in the dappled shade of a
stand of male staghorn sumac trees. The plants bloom every year
in early June, about a metre from the sidewalk shown in the image
Unless you are looking carefully,
the flowers may go unnoticed, since the nearby grass and weeds are
taller, and surround them. The blooms are two to three
centimetres in diameter, and grow on straggly stalks to a height of no
more than twenty five centimetres.
The peas belong to the family
Fabaceae. Many of the
members of this family have become
important commercial or ornamental crops, for example: edible
peas and beans, clover, and sweet peas. The sweet pea is native to
Europe, but has been naturalized over most of North America.
Other common names for the species are the “everlasting pea” or the
“perennial pea”. The image that follows shows the two oval leaves
joined by a short stalk to the main stem. Two additional tiny
leaflets are positioned at the joining point, (called the axil).
A group of immature sweet pea buds
can be seen below. Each bud displays a calyx composed of five
pointed green sepals (modified
leaves). It is interesting to note
that a tiny green filament-like thread grows out from the point of
intersection of each bud’s stem to the main stem.
As the buds increase in size, they
begin to show pink colouration.
Just before blooming, the buds
display their natural bright red colour.
The large outer petal that will
form the flower’s “banner” (see later), opens to reveal the inner
petals of the flower.
Finally, the brilliantly coloured
blooms are revealed. The upper-most petal has a noticeable vertical
groove. This petal forms the “banner”
or “standard”of the
flower. Beneath the banner are two lateral petals referred to as
“wings”. It is these
wings that cause the flower’s structure to
be called papilionaceous,
(like a butterfly). Finally, beneath
the wings are two petals joined to form the “keel”. This keel
encloses the reproductive structures of the flower.
A side view gives a different
perspective . Notice how the two wing petals effectively cover
the top portion of the keel.
Although the flowers in my location
are deep red dappled with white, the colour may range from red through
pink to (rarely), white.
While photographing a sweet pea
flower, I was struck by the elegant form of this remarkable bloom!
Photographed from the back, the
flower shows a lighter colouration, and the five-pointed green calyx at
the base of the petals is visible.
If the two petals forming the keel
are gently removed by pulling on them, the reproductive structures
hidden beneath are revealed. Ten orange-brown anthers (male
pollen producing organs), supported by white filaments, surround the
single hairy green pistil
formed by the stigma (female
organ) supported by a sturdy style.
The flower structure of the
sweet pea allows only one type of insect - the bee, to pollinate
it. The nectar in a flower is stored just over the filaments of
the anthers. As the bee enters the flower, its mass pulls down
the keel, and the anthers and stigma move up to touch the underside of
the bee’s body. The bee gets the nectar, and in so doing, becomes
coated with pollen.
Under the microscope, an anther can
be seen to have many spherical to ellipsoidal pollen grains on its
A photomicrograph of the tip of the
pistil shows both the oval green stigma, and the hairy, lighter green
style that supports it. Many pollen cling to both stigma and
Pollen grains are irregular in
The cellular structure of the
banner petal shows both red and white cells in its makeup.
Pea flowered plants have the
ability to obtain, (or “fix”)
nitrogen from the atmosphere by using
soil bacteria (Rhizobium).
It is this capability that makes such
plants useful, both in the environment, and to farmers, by increasing
About a third of the photographs in
the article were taken with an eight megapixel Canon 20D DSLR and Canon
EF 100 mm f 2.8 Macro lens. An eight megapixel Sony CyberShot
DSC-F 828 equipped with achromatic close-up lenses (Canon 250D, Nikon
6T, Sony VCL-M3358, and shorter focal length achromat used singly, or
in combination), was used to take the rest of the macro images. The
lenses screw into the 58 mm filter threads of the camera lens. 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 photomicrographs were taken with a
Leitz SM-Pol microscope (using dark-ground condenser), and the Coolpix
The following references have been
found to be valuable in the identification of wildflowers, and they are
also a good source of information about them.
- Dickinson, Timothy, et al.
2004. The ROM Field Guide to Wildflowers of Ontario. Royal
Ontario Museum & McClelland and Stewart Ltd, Toronto, Canada.
- Thieret, John W. et al.
National Audubon Society Field Guide to North American Wildflowers -
Eastern Region. 2002. Alfred A. Knopf, Inc. (Chanticleer Press,
Inc. New York)
- Kershaw, Linda. 2002. Ontario
Wildflowers. Lone Pine Publishing, Edmonton, Alberta,Canada.
- Royer, France and Dickinson,
Richard. 1999. Weeds of Canada. University of Alberta
Press and Lone Pine Publishing, Edmonton, Alberta, Canada.
- Crockett, Lawrence, J.
2003. A Field Guide to Weeds (Based on Wildly Successful
Plants, 1977) Sterling Publishing Company, Inc. New York,
- Mathews, Schuyler F.
2003. A Field Guide to Wildflowers (Adapted from Field Book
of American Wildflowers, 1902), Sterling Publishing Company, Inc.
New York, NY.
- Barker, Joan.
2004. The Encyclopedia of North American Wildflowers.
Parragon Publishing, Bath, UK.
Microscopy UK or their contributors.
Published in the July
2006 edition of Micscape.
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