A Close-up View of the Wildflower
"Yellow Toadflax"

(Linaria vulgaris)


by Brian Johnston   (Canada)



One of my childhood memories is being shown how to pinch the sides of this pretty yellow flower in order to "open the dragon's mouth".  At that time, this common weed was referred to as a wild snapdragon.  Today, it is often called butter-and-eggs or yellow toadflax.  This last name was given to the plant because of the flower's supposed resemblance to a small toad, or alternatively, the mouth of a small toad!  I must admit that in my opinion, the comparisons require a very large stretch of the imagination.  To me, the flower looks remarkably like a hypothetical dragon's mouth!  The 'flax' in the name refers to the fact that before flowering, the stems with their long, narrow leaves closely resemble those of flax plants.
 
The image above shows the top portion of a stem with its spike (or raceme) of closely packed showy yellow flowers.  The plant is usually ten to thirty centimetres in height and is normally found in patches formed by the growth of perennial creeping roots.
 
The first image, and the one below, show the unusual shape of the flower.  There are five petals, three on the bottom that are fused except at the tips, and two at the top that are similarly fused.  The petals together form a corolla, (the collective term for the petals of a flower) that has an upper and lower lip.  This lower lip is deep yellow or orange in colour.  Each flower is from 1.5 to 4 centimetres in length, including the long spur at the bottom.




 
A side view of one flower shows the ring of five green bracts (modified leaves) that cup the flower at its midpoint, and connect it to the stem.  The mouth of the flower is normally firmly closed, and more strength than the average pollinating insect possesses is required to push the bright yellow-orange base down to gain access to the stamens.  When a large bee is attracted by the bright colour of the bottom lip of the flower, its mass pushes down the lip to partially reveal the nectar stored in the long spur.  In order to get its proboscis into the nectar, it must push its hairy head into the open bloom.  In so doing, pollen grains from the anthers are transferred to the bee and these are eventually carried to the stigma of another flower resulting in cross-pollination.  (Self-pollination doesn't occur in toadflax.)




 
Notice in the image below, that the unopened flower bud reveals the bottom lip of the flower's mouth.




 
By removing the yellow-orange bottom lip of the flower, it is possible to see the four pollen covered anthers (the male pollen producing organs) arranged as two pairs.  In newly opened flowers, the two anthers in each pair often appear joined.  At a later stage they may separate.




 
A clearer view of the internal contents of the flower can be obtained by removing both upper and lower lips.  Notice that the upper anthers have separated in this bloom.  The pale greenish-white stigma (the female pollen accepting organ) can be seen between the lower filaments and anthers.  The height of the stigma is variable, but it usually is positioned somewhere between the two anther sets.




 
Under the microscope, dark-ground illumination reveals details of one anther and its supporting filament.  Both are covered in pollen.




 
A higher magnification shows that many of the pollen grains seem to be connected by fine thread-like structures.




 
The following photograph shows the ellipsoidal shape of toadflax pollen grains.




 
At the base of the filament that supports the anther, there are finger-like protuberances, green on the side closest to the stem, and gray on the opposite side.




 
These speckled protuberances can be seen more clearly in the images below.






 

 
The greenish-white stigma of a toadflax flower is visible in the bottom left corner of the following image.




 
Dark-ground illumination reveals the style, and the stigma itself more clearly.




 
Although yellow toadflax is considered a noxious weed in many areas of North America, its charming little flowers provide a visual feast for wildflower enthusiasts and a welcome source of nectar for many bees from June to October!
 

 
Photographic Equipment

The low magnification photographs in the article were taken using a Nikon Coolpix 4500 with a combination of natural light and the Nikon Cool light SL-1.  Higher magnification images were taken with natural light using a Sony CyberShot DSC-F 717 equipped with a combination of achromatic close-up lenses (Nikon 5T, 6T and shorter focal length achromat) which screw into the 58 mm filter threads of the camera lens.  (These produce a magnification of from 0.5X to 9X 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 717.  (The magnification here is about 13X for a 4x6 inch image.) The photomicrographs were taken with a Leitz SM-Pol microscope (using a dark ground condenser), and the Coolpix 4500. 


A Flower Garden of Macroscopic Delights

A complete graphical index of all of my flower articles can be found here.


The Colourful World of Chemical Crystals

A complete graphical index of all of my crystal articles can be found here.

 All comments to the author Brian Johnston are welcomed.


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Published in the March 2009 edition of Micscape.
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