A Close-up View of Three Buttercups

All three of the buttercups discussed in this article grow near the edge of a stream which flows through a park in my neighbourhood. (The genus name Ranunculus translated from the Latin means “little frog”. Like frogs, buttercup species live near the water.) The common buttercup is found some distance from the stream, while the other two species grow close to the water’s edge. All buttercups possess distinctively shiny, rather waxy looking, bright yellow petals. This phenomenon is due to a special layer of reflective cells beneath the petals’ surface cells. As you will no doubt notice from the images that follow, this distinctive appearance depends very much on the angle between the light source, the flower, and the eye (or camera lens).

Common (Meadow) Buttercup Ranunculus acris

The species name acris was given due to the fact that the stems and leaves of the plant contain an “acrid” poisonous juice which protects the plant from herbivorous animals.

Common buttercup flowers possess five petals, and have a diameter of about three centimetres. The plant itself can be up to a metre in height, and has a rather thin stem. Flower petals may bend down (convex) at the edge as in the first image, or up (concave) as in the second.

It is difficult, if not impossible, to distinguish between common and swamp buttercup by observing the flowers. They are, for all intents and purposes, identical. What distinguishes the two species is a small difference in the stem leaves. Each of the three-lobed subdivided segments is joined to others without stalks. As you will see in the next section, swamp buttercup leaves have a similar structure, but the segments are joined together by short stalks. The two images that follow show stalkless common buttercup leaves.

Notice, in the image of a bud shown below, the hairless stem, and the five green, extremely hairy, sepals (modified leaves) that surround the bright yellow petals. (The ring of sepals is called the calyx of the flower.)

When the flower first opens, the centre is filled by rings of bright yellow stamens . The image on the right shows that each anther (male pollen producing organ) has a deep vertical groove on its surface.

Notice the many pollen grains that are present on the petals’ surfaces.

Over a several day period, the stamens grow in length and separate. The thin stalks (filaments) that support the anthers become visible. At the centre of the flower, a round mass of light green pistils and their attached immature ovaries is revealed.

Just above the surface of the petals, there is a ring of unusually shaped stamens which possess no anther grooves, and have thicker filaments.

At the base of each petal, close to the mound of green pistils, there is a reservoir which contains the flower’s nectar. When bees and flies alight on the centre of the flower to obtain the nectar, they cannot help but pick up a coating of pollen, which can then be transferred to another flower. This results in cross-pollination. Often, however, such insects disturb the anthers, and pollen falls onto the pistils of the same flower. This results in self-fertilization which is less advantageous to the plant. Since the number of pistils in a buttercup flower is large, the chance of all of them being self-fertilized is not great.

The photomicrograph below shows a single anther, with its two lobes separated by a (lighter) groove. A stub of the filament can be seen at its base.

Side views taken at two different magnifications reveal the many almost spherical pollen grains that coat the surface.

Removal of a flower’s petals, and upper layer of stamens allows a better view of the central mass of pistils, and attached ovaries.

Under the microscope, the inverted comma shape of each of the pistils can be seen clearly. Each pistil has a pollen covered stigma (female pollen accepting organ), a thick supporting style, and an egg-shaped ovary.

Viewed from above, (again under the microscope), the tops of a number of stigmas are covered in pollen.

Here is a single pistil with its yellow pollen coated stigma, darker green style, and lighter yellow-green ovary chamber.

Higher magnification of the pistil in the image above shows cellular detail at the edge of the ovary (left), and the curled tip of the stigma (right).

Buttercup pollen grains are only roughly spherical in shape. They possess none of the interesting detail of many other wildflower species.

Swamp (Marsh) Buttercup Ranunculus septentrionalis

The image above, and the two higher magnification views that follow, show the flower of this species to be identical to that of the common buttercup. The photographs show a newly opened flower with its many stamens packed closely together in the centre of the flower, completely obscuring the group of pistils beneath.

The only observable difference between the two species can be seen below. In swamp buttercup, the leaf segments are joined together by short stalks. (Compare this image with the ones earlier to see the difference.)

Like the earlier species, this one has intensely hairy sepals clasping the unopened bud’s petals.

Both front and reverse views of a flower can be seen below. In the left image, note the round blister-like formation on the top right petal. These are common in buttercup flowers. (I suspect that the upper layer of cells has become detached from the base layer for some reason.) In the right image, you can see the five sepals which line up with the overlaps of the petals.

Two additional images, using higher magnification, show the large number of stamens arranged in rings at the flower’s centre.

Kidneyleaf Buttercup Ranunculus abortivus

This species is quite different in appearance. The flowers are much smaller, 6 to 8 mm in diameter. The species name abortivus refers to this diminished petal size. The petals do not overlap, and there are fewer stamens than in the other species. The leaves at the base (basal leaves) are kidney-shaped, giving the plant its common name. The stem leaves are unstalked and divided into 3 to 5 lobes.

Notice in the images that follow, the striking ellipsoidal (egg-shaped) group of central pistils. In the second image, fine yellow pollen grains can be seen clinging to the upper surfaces of the stigmas.

Both sepals and petals fall from the flower about the same time, leaving a cluster of carpels (immature seeds - better referred to as achenes). Eventually, the cluster elongates to an ovoid shape about 6 mm in length.

Yellow is a common wildflower colour. Buttercup flowers have “value-added” with their dazzlingly shiny surfaces and beautiful structure.

Photographic Equipment

Two-thirds of the photographs in the article 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. 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.

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