Close-up View of
Bouvardia 'Royal Edith'
by Brian Johnston (Canada)
The bouvardia belongs to the Madder
family (Rubiaceae), and is
therefore related to both the coffee plant and the gardenia. The
genus name Bouvardia refers
to the French doctor Charles Bouvard (1572-1658), who was the personal
physician to Louis XIII, and director of the “Jardin des
Plantes”. The cultivar photographed for the article is called
‘Royal Edith’. (A cultivar
is a variation of a species that is produced through deliberate
selection or breeding.)
As can be seen above, bouvardia flowers are composed of slender tubes,
topped by four petals in a cross formation.
The stems of the plant are thin, and branch frequently, resulting in
many clusters of flowers at the branch tips.
One of these clusters can be seen below. Notice that the group
consists of tiny green buds, almost mature flowers, and all
intermediate stages between the two.
Before the bud blooms, the four closed petals, (or corolla lobes), at
the top of the corolla tube form an almost square shape when viewed
from above (left image). The same image shows a partially opened
flower with the lobes forming a concave surface. In the
right-hand image, the top-most bud has just started to open, and the
mature flower’s lobes have become perpendicular to the corolla tube.
The images below, showing the underside of a flower cluster, reveals
several pairs of leaves, and the four small green bracts (modified leaves) that
surround the base of each corolla tube.
Although all of the flowers have a bright red band at the right-angle
intersection of corolla lobe to corolla tube, the colour of the lobe
itself depends on the age of the bloom. When the flower first
opens the lobes are bright pink, but they soon fade to faint pink, or
even to white over a period of 24 hours.
If one of the lobes is examined under the microscope, its cellular
structure is revealed. In some areas, pink, or dark red, cone
shaped structures project up from the lobes’s surface (right image).
A flower cluster at an early stage of development can be seen
below. Notice that the very immature buds lack the corolla tube
that can be seen in slightly older buds.
A number of these very early stage buds can be seen below. Notice
that several of them possess five surrounding bracts rather than the
The greenish colour of a bud is slowly replaced by pink. Notice
how closely the corolla lobes are fused together at this stage.
A little later, the entire bud is bright pink, and the grooves between
the lobes are more distinct.
Eventually, the lobes separate to reveal the interior of the flower.
As the lobes open, the male reproductive structures of the flower
become visible. Four brownish-yellow anthers (male pollen producing
organs) are positioned at the corners of the central square.
Notice the length of the corolla tube compared to the length of the
lobes. Also notice the single rib along the centre line of each
If three of the corolla lobes, and a section of corolla tube are peeled
away, the positions of male and female reproductive structures can be
seen clearly. Each anther is attached to the top of the corolla
tube by a very short filament.
In most flowers the filament extends to the base of the flower, but
this is not the case here. The stigma
(female pollen accepting organ) is held about half way up the corolla
tube by a slender style.
By removing the entire corolla, we can concentrate on the stigma, which
seems to consist of two distinct pale green lobes.
A slight rotation of the flower not only results in a different
background, but also gives a better idea of the real shape of the
stigma. At this magnification, it is just possible to resolve the
dimpled surface of the stigma.
The microscope gives a closer view, but at the expense of a diminished
depth of field. The microscope has been refocused to show both
lobes. Even this magnification is insufficient to resolve the
true nature of the stigma’s surface.
The stigmal epidermal (surface) cells can be seen clearly in the two
images that follow. The rounded protuberances can be seen in a
side view (left), and front view (right).
Two additional images of stigmal epidermal cells, using a still higher
magnification, can be seen below.
As was mentioned earlier, the four anthers are positioned at the points
of contact of the four corolla lobes. Yellow pollen stands out
against the red background in the right-hand image.
Here is a closer view of the top of the corolla tube. The
filaments holding the anthers in position are so short that they are
blocked from view by the anthers. (Notice the hairs growing on
the inner surface of the corolla tube near the stigma. Could
these be useful in dislodging pollen from the proboscis of a visiting
The upper surface of the corolla tube seen in the photomicrographs
below is covered with many pollen grains. Note the out-of-focus
anther in the upper left corner of the first image. By focusing
on a plane in front of the one seen in the first image, it is possible
to visualize the many hairs that cover the upper surface of the corolla
tube. (These hairs are much smaller than those seen in the image
Higher magnification of the hairs reveals adhering pollen grains
(left), and the microscopic surface detail of a hair (right).
The cellular structure of the red upper portion of the corolla tube
(left), and area near the anther (right) can be seen in the
photomicrographs that follow.
The front surface of an anther can be seen in the two images
below. The roughly ellipsoidal pollen grains appear to have
several longitudinal grooves on their surfaces.
A side view of the same anther reveals the short filament and its point
of attachment to the corolla tube.
Beneath the flower clusters, there are many bright green leaves which
occur in pairs on the stem, opposite one another.
The back surface of a leaf has an interesting contoured vein structure.
Photomicrographs (using two magnifications) of the cellular structure
of the upper surface of a leaf can be seen below.
The lower surface of a leaf has many elliptical stoma, and their
associated guard-cells that control gas entry into the inner structure
of the leaf.
Bouvardia’s fragrant scent, and spectacular flowers, make it a welcome
addition to any home. I hope that the images in this article have
given the reader an appreciation of its interesting macroscopic and
Most of the macro-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. A Canon 250D achromatic close-up lens was used to obtain
higher magnifications in several images.
A few 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.
The photomicrographs were taken with 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
February 2009 edition of Micscape.
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