A Close-up View of a Prairie Mallow Hybrid
View of a
Prairie Mallow Hybrid
by Brian Johnston (Canada)
The Mallow Family, (Malvaceae), is best known for its
spectacular blooms, as illustrated by the Hibiscus, Hollyhock, and
Rose-of-Sharon plants. Even the lowly Common Mallow (Malva neglecta), considered by many
to be a pestilential weed, is a family member.
malviflora, Prairie Mallow, is a wildflower native to high
coastal meadows, and open woodlands from Oregon to northern Baja.
It is often called ‘Checkers’, ‘Checkerbloom’, ‘Dwarf Checker-mallow’
or ‘Dwarf Checkerbloom’ because the flowers are approximately the size
of a checker game piece. The plants have round, lobed basal
leaves, upright stems with deeply cut upper leaves, and a spike of
funnel-shaped flowers that possess a prominent pistil. ‘Little Princess’, the cultivar
studied in this article, resembles a miniature Hollyhock with striking
The first image in the article, and
those that follow show why this cultivar is so highly valued by
gardeners. Each flower spike is simply ‘pretty as a picture’!
This profusion of pink blooms
begins as a group of green, ridged buds with pointed tips. There
is no hint at this point of the flowers’ eventual colour. In many
bud spikes, the upper-most members are difficult to distinguish as buds
at all, and have a white or very faint pink colouration.
If we move closer to the
early-stage buds, we see that their coating of fine hairs is
particularly dense along the ridges.
The ‘rogue’ bud spike shown in the
three images that follow has some buds with an unusual orange-pink
colouration. This is certainly not typical, and while normal buds
are enclosed by a ring of green sepals (modified leaves), the rogue
ones possess these strangely coloured ones.
A typical bud begins to bloom when
the ring of sepals (called the flower’s calyx) splits apart near the
top, and the flower’s petals become visible.
The green sepals have stopped
growing, but the tightly packed whorl of petals (called the flower’s
corolla) continues to lengthen. Four images follow that show
examples of this process.
Eventually the five overlapping
petals that form the corolla open out to form a roughly cup-shaped
bloom. Notice that each pink petal is attached to the flower’s
stalk by a stubby, narrow, white base. This adaptation results in
five distinctive oval ‘gaps’ that add visual interest to the opening
Over the period of a couple of
days, a flower transitions from closed bud, to cup-shaped young bloom,
to a final mature flower with an ‘almost’ flat surface. Examples
of this transition can be seen in the two images that follow.
Projecting from the flower’s centre
is a sturdy, pale-pink stalk which supports its reproductive
structures. At this point however, only a mass of dark, almost
black anthers coated with beige pollen grains is visible. The
pistil has yet to put in an appearance.
This situation is short-lived
however. Soon, the flower’s bright red, multi-lobed stigma lobes
are pushed out from beneath the forest of anthers by the lengthening
In the cup-shaped young flower
shown in the image on the left, the pistil is not visible, while in the
mature, flat flower shown on the right, the stigma lobes are
As the style continues to lengthen,
the red stigma lobes are pushed farther away from the group of anthers.
malviflora’s petals are rough in appearance due to the large
number of three-dimensional longitudinal veins that cover their
Photomicrographs of a petal’s
surface show the wide range of colouration of its constituent cells
(left image), and their jigsaw-puzzle-like shape (higher magnification
Similar photomicrographs showing a
different area on the petal are shown below.
To me, the shape of the flower’s
dark anthers resembles an assortment of chromosomes!
The sequence of images that
follows, (taken with increasing magnification), reveals the structure
of the flower’s pistils, and the spherical shape of Prairie Mallow
For comparison, here is a view of
the jumbled mass of anthers and their supporting filaments taken using
macrophotographic equipment (left), and photomicrographic equipment
Most Prairie Mallow pollen grains
are perfectly spherical, and are covered with short, spike-like
projections. Strangely, several grains (in the first two images)
look like deflated beach balls!
Notice that when the stigma is
pushed by the lengthening style up through the mass of pollen covered
anthers, its lobes are packed tightly together in a column (left
image). If the stigma of a flower comes into intimate contact
with its own pollen during its passage up through the anther mass, why
doesn’t self-pollination occur? (Self-pollination is detrimental
to the long term viability of the species.) In order to
discourage self-pollination, the receptive surfaces of the stigma lobes
are facing one another, and are in close contact until the stigma has
passed through the danger zone. Only later do the lobes separate
to reveal fresh receptive surfaces to visiting insects (right
image). Thus cross-pollination is favoured.
A number of images follow that show
views of the separated stigma lobes of two Prairie Mallow
flowers. In one, there appear to be 8 lobes, while in the other 9
lobes are present.
The two photomicrographs below show
the body of a stigma lobe. Notice that the red receptive surface
is covered with hair-like projections that help to acquire and retain
Additional photomicrographs reveal
the tip of a stigma lobe. It’s easy to see that if the ‘hairy’
receptive surfaces of all of the lobes were facing one another in a
columnar structure, pollen grains could not adhere to the hairs, thus
largely preventing self-pollination.
Here are two additional
photomicrographs that show pollen grains adhering to a stigma lobe tip
(left image), and the surface of an anther (right image).
Once pollination has occurred, the
column that supports the stamens and pistil dries up and falls
off. All that is left of the flower is the ring of sepals and the
Now let’s look more closely at the
plant’s leaves. Near the top of the stem, the leaf has a palmate
shape with extremely deep lobes.
A little lower on the stem, the tip
of each lobe is itself lobed.
Farther down the stem, the base
leaf shape is still palmate, but the base lobes are less deep.
As we continue to move down the
stem, the depth of the base lobes continues to decrease.
At the base of the stem, a leaf’s
shape is very different when compared to one positioned just beneath
the flower spike.
The two images below show higher
magnification views of the glossy upper surface of a leaf.
A photomicrograph of its
under-surface follows. Note the many oval stomata and guard cells
that control gas entry into and out of the leaf.
The image on the left reveals the
cellular structure of the upper surface of a leaf. On the right
is a photomicrograph showing one of the spike-like hairs that grows
from the leaf’s edge.
Prominent veining is visible on the
underside of one of the plant’s lower leaves.
Higher magnification views of this
vein structure follow.
At low magnification the fine hairs
that grow from a leaf’s surface are not visible. The higher
magnification view on the right shows them clearly.
Extremely sharp spikes grow in
pairs from the surfaces of a leaf’s veins.
Not only is Sidalcea malviflora ‘Little Princess’
a visual feast for the eyes, but it is also easy to grow. In
fact, if grown in moist soil with full sunlight, it may bloom through
the summer, and into the fall!
The low magnification, (to 1:1),
macro-photographs were taken using a 13 megapixel Canon 5D full frame
DSLR, using a Canon EF 180 mm 1:3.5 L Macro lens.
A 10 megapixel Canon 40D DSLR,
equipped with a specialized high magnification (1x to 5x) Canon macro
lens, the MP-E 65 mm 1:2.8, was used to take the remainder of the
The photomicrographs were taken
using a Leitz SM-Pol microscope (using a dark ground condenser), and
the Coolpix 4500.
A Flower Garden of
A complete graphical index of all
of my flower articles can be found here.
The Colourful World of
A complete graphical index of all
of my crystal articles can be found here.
Microscopy UK or their contributors.
Published in the May
2011 edition of Micscape.
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