Close-up View of Three Extraordinarily Small Wildflowers
Common Knotweed (Polygonum arenastrum)
Sorrel (Rumex acetosella)
Brian Johnston (Canada)
suspect that most readers of this article have crushed countless
thousands of these unique wildflowers underfoot as they walk across
lawns or grassy recreation areas. Even if you stooped to have a
look at the unsightly green weeds, the flowers are almost too small to
be seen with the naked eye. The average diameter of the blooms
discussed here is 2 to 3 mm. They are so diminutive in fact, that
they present problems for macro-photography, not the least of which is
simply obtaining sufficient magnification.
Two of the three plants, (the first
and third), are members of the family Polygonaceae,
which when translated from the Greek means “many knees”. This
refers to the stems, which are jointed and have many swollen nodes or
‘knees’. The flowers are small and ball-like, and form in
- groups of racemes (an unbranched cluster in
which each flower is attached by its stem to the central stem),
- spike-like panicles (a branched flower
structure in which the main branches are also branched),
One of the most distinctive
characteristics of the family is the ocrea,
a membranous sheath that encloses the junction of stem to branch.
The remaining plant, (the second),
is a member of the Amaranthaceae
Common Knotweed (Polygonum arenastrum)
Common knotweed was introduced into
North America from Europe about 1809. It is known by many names,
a few of which are: bird’s tongue, matgrass, pinkweed, knotgrass and
waygrass. The general appearance of the plant is rather mat-like,
with many stems growing out from a central taproot. Although most
stems grow parallel to the ground, some do grow upward a short distance
- about 10 cm in my samples. As can be seen below, the stem
branches frequently, and the leaves are alternate and oval in
shape. The flowers grow out from the leaf axils, (the point of connection of
the leaf to the stem). The image on the right shows the
transparent ocrea that encloses each axil.
The three photographs that follow
show a variety of stages . Multiple buds grow from each
axil. The red ‘petals’ are not petals at all, but sepals (the outermost part of a
flower). What appear to be red buds, are actually a later stage
of development after fertilization has taken place.
The flowers of common knotweed have
five sepals, 2 to 3 mm long, which are green at the center and white or
pink-tinged in their outer area. Flowers contain variable numbers
of stamens (the male pollen
producing organs) and two or three pistils
(the female pollen accepting organs) The brilliant red
colouration of the sepals seen in closed blooms happens after
fertilization. The red sepals then enclose the developing fruit.
The fourth image above shows the
thin membranous ocreas clearly. If a section of the ocrea is
examined under the microscope, its cellular structure is clearly
If you look closely between the
yellow anthers, you can see the green tops of several stigmas.
Examination of the image below
shows that each yellow anther is connected to a thin green filament
with a bulbous base.
The two photomicrographs of a sepal
that follow show the many yellow pollen grains that adhere to its
If you examine the red structure
immediately behind the white bloom, you can see the tip of a dark brown
seed protruding out from the now closed, and bright red sepals.
Another example follows. In
this case the sepals enclosing the seed have still retained much of
their original colour but tinges of red can be seen. The dark
brown, egg-shaped, three-sided fruit contains one seed.
The genus name Chenopodium is
derived from the Greek cheno
meaning ‘goose’ and podion
meaning ‘foot’. This refers to the shape of the leaves.
Images from various references indicate that the leaf shape for this
plant is very variable, and the leaves at the top of the stem look very
different from those at the base. (All of my images are taken of
the tips of stems at the top of plants.) Notice the red and
purple striped stem in the second image. In this strange
inflorescence (group of blooms), the light
green, five lobed structures (called perianth members), are the unfertilized blooming flowers.
All parts of the plant are covered
with very tiny scales which appear as white specks. A fertilized flower begins to turn a yellow-orange colour.
A little later, the fertilized
flower becomes bright orange, and at the center, the brown ovary that
will eventually develop into the fruit, becomes visible.
As time passes, the orange lobes
open up to reveal the mottled brown fruit which appears to be partially
held in place by strange white strap-like appendages.
At a later stage, the fruit darkens
to almost black. The second image shows its round triangular
Finally, the fruit drops from the
flower leaving the now completely open tepals,
(indistinguishable petals and sepals), and their dangling
straps. As the tepals age, they turn from orange to brown.
Note the lighter coloured band around the edge of the tepals.
Of the many wildflowers that I have
photographed, this species is one of the smallest and also one of the
Sheep Sorrel (Rumex acetosella)
Sheep sorrel, or red sorrel as it
is sometimes called, is easily recognized by its distinctive
arrow-shaped leaves, one of which can seen in the image on the right
below. The tiny flowers grow at the ends of green stalks which
branch off the main stalk. The plant is dioecious because male and female
flowers grow on separate
plants. Sheep sorrel has a sour taste because it contains high
levels of poisonous oxalic acid, particularly in the leaves.
The male flowers of the plant are a
mixture of red and yellow, and hang on short stalks from the
stem. The flower has no petals, but 6 sepals (petal-like
structures). The open flower which is about 2 mm in diameter, has
a number of projecting stalks that once had anthers attached.
These have fallen off.
Under the microscope, the cellular
structure of one of the globular closed flowers can be seen more
Two views of the point of
connection of the flower stem to the base of the flower are shown in
the photomicrographs below.
The cellular structure of a
filament that once supported an anther, (the male pollen producing
organ) can be seen below.
Notice in the two images that
follow, the red bell-like anthers hanging from the filaments of flowers.
Photomicrographs of a single sepal
can be seen below, at low and high magnification.
Two additional photographs showing
dangling anthers reveal different anther colourations from those shown
earlier. Here they are yellow-beige in colour rather than red.
The final two images show the
surface of two anthers, one covered in pollen and one without.
I hope that the images in this
article give you a greater appreciation of a group of wildflowers that
are “size challenged” and therefore not commonly viewed by amateur
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), was used to take all 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 a
dark-ground condenser), and a Nikon Coolpix 4500 camera.
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.
- or heads (a crowded cluster of flowers
which may or may not have stalks).
- 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, NY.
- Mathews, Schuyler F.
2003. A Field Guide to
Wildflowers (Adapted from Field Book of American
Wildflowers, 1902), Sterling Publishing Company, Inc. New York,
- Barker, Joan.
2004. The Encyclopedia of North
American Wildflowers. Parragon Publishing, Bath, UK.
Microscopy UK or their contributors.
Published in the August
2007 edition of Micscape.
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