A Close-up View of a Hybrid Passion Flower Passiflora belotti

When you take a flower in your hand and really look at it,
it's your world for the moment. I want to give that world to
someone else. Most people in the city rush around so,
they have no time to look at a flower. I want them to see
it whether they want to or not.

- Georgia O'Keeffe (Artist)

In an earlier Micscape article, I investigated two members of the Passifloraceae family – Passiflora caerulea, and Passiflora coccinea x incarnata. In this article, I will describe the extremely beautiful hybrid Passiflora x belotti, which was produced by crossing P. alata with P. caerulea. Unlike the other two species, this one has an absolutely wonderful scent.

In 1824, Dr. Lindley named this hybrid Passiflora alato-caerulea, and over the years it has been given other names: Passiflora munroi, Passiflora pfortii, Passiflora x belotii, etc. Today, one of the commonest names is Passion Flower ‘Imperatrice Eugenie’. The dedication is to the wife of Emperor Napoleon III.

All Passion Flower blooms are strikingly complex, and seem almost alien when compared with simpler flowers. Sepals, petals, coronal filaments, and reproductive structures all combine to form an amazing botanical spectacle.

As usual, my purpose is to show that the beauty of a flower, when viewed from a distance, is only part of the picture. When viewed close up – very close up, the structures that combine to form the flower have a beauty all of their own! (Note: As the camera moves closer to a large flower, it becomes more and more difficult to keep everything in the picture in focus. Photographers refer to this as a ‘depth of field’ problem, and it requires a particular part of the flower to be chosen to be ‘in focus’. In the image on the left below, I have chosen the purple coronal filaments to be in focus, while in the image on the right, I have chosen the more distant reproductive structures to appear in focus.) If you look at the image on the right, you will notice that the flower’s reproductive structures (stigmas, ovary, and anthers) are held by a sturdy green, rod-like structure which is called the androgynophore.

As the camera moves closer to a flower, this depth of field problem becomes more severe.

A mature Passion Flower bloom can be seen below. What however, did the bud stage look like?

The answer can be seen in the image that follows. Keep in mind that the Passion Flower plant is a vine that holds itself aloft by having its tendrils curl around nearby plants, or other inanimate structures. One such tendril can be seen in the image. Notice in particular, the strange, tiny bulbous structure growing from the leaf stalk, just to the right of centre in the image. This is a nectariferous gland.

Much closer views of a nectariferous gland can be seen below. These glands produce a sweet, viscous liquid called nectar that attracts insects. In some species, the nectar attracts insects to help fertilize the flower, and other species, it attracts insects that devour a particular predator that might eat the plant’s tissues, or suck the juices from them.

Three additional images that show these glands can be seen below. If no insect partakes of the liquid refreshment supplied by the glands, the droplets become so large that surface tension can no longer hold them in position, and they fall onto whatever is immediately beneath.

Let’s return to the bud-stage of the blooming process. The bud is protected by three modified leaflets. Within this protective envelope, there are five sepals (modified leaves) which in turn protect the flower’s petals. Each sepal is tipped by a slender spike.

These modified leaflets and sepals can be seen more clearly in another bud.

Notice the interesting structural engineering involved at the point of connection of a bud stalk to the main vine. The two stalks which angle directly left are connected to leaves.

Tendrils that have not come into contact with something to hold on to, seem to form neat, regular coils.

However, when a tendril does find a ‘foot-hold’, it certainly seems to make certain that it won’t be dislodged!

Over a period of many days, each bud grows in overall size, with its length increasing faster than its diameter. Notice that the length of the sepal spikes has not kept up with the overall growth.

Eventually, the sepals begin to separate as the time of blooming approaches. This reveals the pale pink colouration of the flower’s petals beneath.

This stage can be seen more clearly in the images that follow. Both the sepals and petals of the Passion Flower are thick and fleshy. If you look carefully, you can see that the sepals have begun to lose their green colouration along the edges. Interestingly, the inner surface of each sepal is white.

In order to see what was inside a bud before it bloomed, I cut away the outer structures. The result can be seen below. Notice how neatly packed are all of the flower’s component parts! A ring of purple coronal filaments encloses the just visible yellow anthers, and almost white stigma pads.

The higher magnification macro-photographs that follow show the blotchy purple and white colouration of the coronal filaments.

A different angle reveals the packed reproductive structures within the bud.

The tips of some of the coronal filaments begin to curve as soon as the restriction caused by the outer envelope of petals is removed.

Within the bud, the stigma pad and green supporting style have fully formed, ready to open out to their final position in the flower.

Two views of the receptive surface of a stigma pad reveal that the surface is covered with microscopic projections. These increase its surface area, and thus increase the probability of pollen capture when the flower blooms, and insects visit.

Once a bud opens – a process that takes a couple of hours – the flower is revealed in all its complex glory. In the image that follows, the five outer, paler ‘petals’ are actually the sepals mentioned earlier. The five pinkish-red structures are the real petals.

Viewed from the back, the three leaflets that protected the bud are visible, as are the five green-backed sepals. Five pink petals can be seen in the gaps between the sepals.

If the three leaflets are removed, the bulbous base of the flower becomes visible. In many flowers this might be the ovary, but not in this case – as we will see later. (Notice the interesting pie-shaped segments in the base.)

If in addition to the leaflets, the sepals and petals are removed from the flower, the multiple rings of coronal filaments become visible. The flower stalk is not strong enough to support the weight of the flower, and so it usually rests on a lower part of the plant, or simply hangs down.

It’s finally time to take a closer look at the flower’s reproductive structures. Closest to you are the three stigmas, held at approximately 120 degree angles by their styles. (Notice that the receptive surfaces of the stigmas are facing away from you.) Next comes the pale green, almost spherical ovary. Beneath the ovary are the five yellow anthers (again facing away from you), each supported by its sturdy, yellow-green filament.

The closer view shown below reveals these structures more clearly.

Each stigma pad (facing down, and pale yellow in colour) is connected to its green, supporting filament in a particularly sculptural way.

Similarly, each downward facing anther is connected to its supporting filament. Here however, the connection between them is a thread-like ribbon of tissue which permits the anther to wobble about if the flower is moved, or if there is air movement around the plant.

The lower surface of the anther is liberally coated with pollen. Notice the raised sections of the anther’s surface at the edges, and down the middle.

In order to obtain the following images, I carefully cut transversely through the flower’s ovary to remove the top-most section of the androgynophore containing the styles and stigmas.

This allows the filaments and anthers to be more easily seen.

Next, I cut transversely through the base of the androgynophore to remove the male reproductive organs. This allows the multiple layers of coronal filaments to be completely visible. The long filaments form the flower’s outer corona. If you look closely at the right-hand image, you will see that near the centre of the flower, there are several rings of much shorter filaments. These form the inner corona of the flower.

Passiflora x belotii plants sometimes have slight variations in colour. One of these variations is the number of white bands that occur on the coronal filaments.

Some botanists believe that the concentric coloured rings, or bands, visible in the flower are a mechanism to guide insects towards the centre of the bloom where the nectar is to be found. Of course, on the way to this sugary treat, the insects may come in contact with anthers and stigma, and therefore promote fertilization.

Where exactly is this nectar to be found? It is held in a shallow, donut-shaped reservoir around the (stub of the) androgynophore. The circular outer wall of this reservoir is within the wide purple band that can be seen in the images below.

The shallow reservoir containing the flower’s nectar is the light (almost white) ring around the androgynophore stub. The purple ridge holding the nectar in place is called the limen. The ring of very short coronal filaments just beyond the ridge is called the operculum.

The two images that follow show the tops (left image), and bases (right image) of the inner corona filaments.

In the image below, the ring between the limen and operculum can be seen to have a rough, purple-spotted surface.

The two images that follow show the wall-like limen that contains nectar. In both images, it is just possible to see the shiny surface of the sticky liquid.

Finally, a brief look at this plant’s leaves. All are three-lobed, with mature leaves being dark green, and young ones a lighter shade of green.

Images of the upper (left), and lower (right) surfaces of a leaf reveal the irregular vein pattern on it’s surface.

Passiflora flowers look almost good enough to eat. This would however, be a very bad idea, since the plant contains poisonous alkaloids (e.g. passiflorine), and cyanogenic glucosides (e.g. hydrocyanic acid). Tissues of the plant may also contain calcium oxalate crystals, which are also poisonous.

As a macro-photographer, I particularly enjoy capturing unusual, complex flowers and their structures. Passiflora hybrids are just about as good as it gets!

Photographic Equipment

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.

An 8 megapixel Canon 20D 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 images.

Reference

Zomlefer, Wendy R. 1994. Guide to Flowering Plant Families. The University of North Carolina Press, Chapel Hill & London.

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.

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