A Close-up View of Three Extraordinarily Small Wildflowers

Common Knotweed  (Polygonum arenastrum)

Common Lamb's-Quarters  (Chenopodium album)

Sheep Sorrel  (Rumex acetosella)

by Brian Johnston   (Canada)

I 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

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 family.

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 visible.

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 surface.

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.

Common Lamb’s-quarters  (Chenopodium album)

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 shape.

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 strangest!

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 clearly.

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 naturalists.

Photographic Equipment

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.

 All comments to the author Brian Johnston are welcomed.

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