Motherwort grows in the shade of a row of Black Locust trees near where I live.  My plan over the summer was to record the life cycle of this strange plant with a view to writing an article for Micscape.  Imagine my horror when, for the first time in many years, the city decided to enhance the appearance of municipal areas by frequent “weed-whacking” of all non-grassy areas!

I needn't have worried.  In his 1977 book about weeds, Lawrence J. Crockett describes them as “wildly successful plants”.  How true!  Every time the plants were cut off at ground level, within a week, new sprouts had begun to sprout and shortly thereafter, I had fresh, new plants to photograph.

As you can see above, Motherwort is not a typical looking wildflower.  Careless handling can result in painful punctures produced by the sharp spines that can be seen beneath the flower.

The plant is a member of the Mint family, as are such common plants as basil, mint, oregano and sage.  The genus name Leonurus derives from the Greek words leon, meaning “lion” and oura meaning “tail”.  A mature plant has many white, fuzzy hairs associated with the blooms and this fact probably suggested the name.  The species name cardiaca is based upon its use by herbalists for heart problems.  Historically, a tea made from the plant was used to treat mothers during childbirth and this resulted in the common name Motherwort.

A mature plant is shown below.  Although Motherwort commonly grows as high as 1.5 metres, my subjects were an average of 25 centimetres in height.  Notice the distinctively shaped leaves and the large number of pink flowers.

Some plants seem to be hairier than others.  The one below is a good example.

Numerous small green buds surround the topmost part of the growing plant.

In contrast to an earlier example, this plant is relatively hairless.  It is therefore much easier to see the rings of spikes that occur at the points where leaf stalks meet the stem (the leaf axils).  Positioning one’s fingers in such a way that the plant can be grasped painlessly, is difficult.

The spiked “collar” is actually formed by a ring of tubular green calyxes which surround immature flowers and remain after the flowers shrivel up and fall off.  (A calyx is a ring of modified leaves, called sepals, that grow immediately under the petals of a flower.)

The Motherwort flower has five petals (which form the corolla), two of which form the pink hairy hood, or upper lip.  In this plant it is not possible to distinguish the two, and only a single lobe is visible.  The other three petals form the darker red, three lobed lower lip.  These petals are fused together further into the tube.  There are 4 anthers (male, pollen producing structures) in two pairs:  an upper and a lower.  The single stigma (female, pollen accepting structure) is positioned between the top pair of anthers but is not visible in the photograph.

Under the microscope the stigma can be seen to possess two lobes, one of which has several pollen grains clinging to it.  The two dark red stalks are the filaments to which anthers are attached.

The surface of one of the four anthers can be seen in the image below.  Several groups of colourless spherical pollen grains are present, as is a single white hair which has become detached from the flower.

Another view of an anther shows its rough surface.

A higher magnification photomicrograph of one of the white hairs shows the unusual “join” in the stalk.

When the Motherwort plant first appears in the Spring, it forms a rosette (flattened spiral arrangement) of bright green leaves.

Later, the mature plant displays the distinctively shaped leaves that can be seen below.

Both upper and lower surfaces of these leaves are covered with very tiny short hairs.

Once a flower has been fertilized, it falls off leaving the green calyx with its five spikes.  As can be seen below, each calyx has two distinctive grooves which form a cross or X shape.  These grooves form the outline of the four developing fruit, called nutlets.  At a slightly earlier stage, these grooves are obscured by a tuft of white hairs.

As time progresses, the calyxes begin to dry out and take on a brown colouration.

The stem of a Motherwort plant is very strong and square in cross-section.  There are numerous longitudinal ridges on its surface.

Using a higher magnification the details of a single immature calyx are revealed.  Note the five spikes, three forming a cross at the top and two which curve downward.

A little later the developing nutlets have begun to turn dark brown.

Much later, the material of the calyx has become translucent and appears light brown.  Eventually, the structure of the calyx begins to break down, dislodging the four nutlets and allowing them to fall to the ground.

Motherwort is an example of a wildflower that doesn’t overtly display its charms, and is therefore often relegated to the “noxious weed” category.  On closer inspection however, its unusual flowers are quite striking, and well worth some study.


Photographic Equipment

The photographs in the article were taken with an eight megapixel Sony CyberShot DSC-F 828 equipped with achromatic close-up lenses (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 photomicrographs were taken with a Leitz SM-Pol microscope (using a dark ground condenser), and the Coolpix 4500.  


References

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, NY.

• 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.