Close-up View of Three Buttercups
Common (Meadow) Buttercup Ranunculus acris
Swamp (Marsh) Buttercup Ranunculus septentrionalis
by Brian Johnston (Canada)
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).
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
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
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.
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
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.
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
Yellow is a common wildflower
colour. Buttercup flowers have “value-added” with their
dazzlingly shiny surfaces and beautiful structure.
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.
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,
- 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.
Microscopy UK or their contributors.
Published in the
November 2006 edition of Micscape.
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