A 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 normal four.

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 lobe.

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 insect?)

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 above.)

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 microscopic features.

Photographic Equipment

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 Macroscopic Delights

A complete graphical index of all of my flower articles can be found here.

The Colourful World of Chemical Crystals

A complete graphical index of all of my crystal articles can be found here.

 All comments to the author Brian Johnston are welcomed.

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