A Close-up View of the Wildflower

 "Sulphur Cinquefoil"


(Potentilla recta)


by Brian Johnston   (Canada)

Sulphur cinquefoil, also referred to as rough-fruited cinquefoil, is native to the Eastern Mediterranean area, and is a member of the rose family (Rosaceae).  The first documented appearance in North America occurred in the early 1900’s in Ontario, Canada (where I live).  By the late 1930’s the species had spread throughout the northwestern United States.  Today, the invasive nature of this beautiful wildflower makes it very undesirable both economically, and ecologically.  It is therefore often referred to as a “noxious weed”.

I have chosen in the image above to show the flower as it often appears - without petals.  Sulphur cinquefoil loses its petals soon after blooming.  The slightest disturbance, usually from the wind or handling, causes the petals to fall.  Since all of my macro-photographs are taken indoors, this presents a real problem.  In the end, the only solution was to bring back a larger number of plants than was necessary, and hope that at least a couple of stems would retain their flowers.  (The plant is easy to remove from the ground, as it possesses a single short taproot with many shallow spreading rootlets.)

A typical plant with a complete flower can be seen below.  The stem supports many leaves along its length, with the buds and blossoms concentrated at the top.



The leaves are palmately compound, with 5 or 7 toothed leaflets making up each leaf.  Leaves have hairs on their surfaces and edges.  The leaf stem is also intensely hairy.



The pale yellow 2.5 centimetre diameter blooms of the plant contain 5 deeply notched heart-shaped petals.  The “sulphur” in the common name refers to the petals’ light yellow colour. The name “cinquefoil”, of French derivation, refers to the five-parted leaves.  (The genus name Potentilla derives from the Latin potens meaning “powerful”, and refers to the medicinal qualities attributed to the plant historically.  Recta, the species name, refers to the upright orientation of the stem.)



When the bud first forms, the five long bracts (modified leaves) that surround it are parallel to its sides.



Later, these bracts open out to reveal five shorter, wider sepals (modified leaves).  As the flower begins to bloom, these sepals open to reveal the coloured petals.  Notice that all stems, bracts, and sepals are covered by long, fine hairs.



Eventually, the petals open enough to reveal the darker yellow reproductive structures within the flower.



Three images follow that show a sulphur cinquefoil plant in full bloom.  It is difficult to imagine how so beautiful a plant could be referred to as a noxious weed!





A close-up of a flower’s centre reveals the many stamens with flat, elongated, disk-shaped anthers (male pollen producing organs), and slender supporting filaments.  Within the ring of stamens is a dome-shaped mound formed by many pistils composed of stigmas (female pollen accepting organs), and supporting styles.



Under the microscope, one can see the basic structure of a stamen.  The pollen grains appear to be concentrated around the outer edge of the anther, and a few can be seen clinging to the upper portion of the filament.



Higher magnification reveals that the pollen grains are ellipsoidal in shape.



Still higher magnifications using dark-ground (left), and phase-contrast (right) illumination show slight variations in the basic pollen shape.



A pistil with its attached white ovary can be seen below.  The flattened yellow top is the stigma, while the yellow-green structure supporting it is the style.  (Note that the out-of-focus ovary to the left of the style belongs to another pistil.)  The image at right shows a group of pollen grains clinging to the ovary’s surface.



Two views follow that show the rather uneven bumpy surface of the stigma.  Note the columnar cells on the surface of the style in the image at right.



Sulphur cinquefoil plants show great variation in the colour of the central portion of their anthers.  Notice in the flowers that follow that the central area is dark brown.  If you compare these with the anthers of flowers shown at the beginning of the article, you can easily see the remarkable difference.  (At first, I thought that the anthers darkened with age, but this seems not to be the case.)





Once the wind has removed the petals from a flower, what remains is still quite striking.  Notice the inner ring of sepals, and outer ring of bracts in the images that follow.  In this species, (Potentilla recta), the flower’s petals are significantly longer than the sepals and bracts.





In another plant, the central portions of the anthers are coloured a lighter brown.







If one examines the tip of one of the green bracts under the microscope, the myriad of fine, almost transparent hairs can be seen clearly.



The final images show the flower-heads of a plant about a month after they have completed blooming.  The sepals and bracts are still green, but the anthers are long gone and the pistils and ovaries have turned a dark red-brown colour.  In the third image the bracts and sepals have been removed to show the developing fruit which consists of a aggregate of achenes (seeds).  The lighter brown projecting structures are the remnants of the flower’s styles.







The sulphur cinquefoil is a close relative of the strawberry plant.  The flower of the cinquefoil is larger and more beautiful than that of the strawberry.  On the other hand, the fruit of the strawberry is more appealing, both visually and gastronomically!


Photographic Equipment

Two thirds of the macro-photographs were taken with 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. 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 remainder of the photographs were taken with an eight megapixel Canon 20D DSLR equipped with a Canon EF 100 mm f 2.8 Macro lens which focuses to 1:1. 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.



 All comments to the author Brian Johnston are welcomed.


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