A Close-up View of Two Passion-Flowers:

Passiflora caerulea &
Passiflora coccinea x incarnata {Hybrid}

by Brian Johnston   (Canada)

About a year ago, a member of an internet photography forum asked for comments about his image of a bizarre flower.  The first couple of responses concluded that the photograph was a hoax created by the accomplished use of Photoshop tools!  Eventually, a horticulturist identified the beautiful and complex bloom as a passion-flower. 

At the time, I had never seen any members of the passiflora family, and when summer arrived, I determined to find some examples to photograph.  The present article is the result.  The first section deals with a single species, while the second concerns a colourful hybrid.

Blue Passion-Flower – Passiflora caerulea

This species is native to southern Brazil and Argentina, and is found as a twining vine that sometimes grows to a height of nine metres!  (My plant was a diminutive 0.6 metres high.)  In tropical areas, the plant is an evergreen, but in cooler climates, it is deciduous.  It has been grown all over the world since Victorian times, and is the one most often found for sale in garden centers.  Strangely, the leaves may have from three to nine lobes depending on the individual plant.  Flowers last for a single day.

The image below shows a typical flower containing five petals alternating with five sepals.  Although both are the same size, and waxy-white in colour, the sepals can be distinguished by their green hook, or awn at the tip.  Two light-green unopened buds can be seen beneath the bloom.

The following illustration shows the positions of petals and sepals as well as the very unusual and conspicuous corona, consisting of many radial rod-like filaments.  Each filament is purple at the root, white in the center, and light blue at the tip. The blue filament tips give the flower its common name.  It is thought that these differently coloured concentric rings guide insects, (and humming-birds), to the nectar at the center of the flower.

Blue passion-flower reproductive structures are shown in the image, and illustration below.  There are three stigmas, (female, pollen accepting organs), with their supporting styles joined together just above the ovary, (the seed producing structure).  Beneath the ovary are the five anthers, (male, pollen producing organs), each supported by a broad green filament.  Notice that both stigmas and anthers face away from the viewer in the photograph.

When the flower first opens, all five of the anthers are positioned in such a way that the yellow, pollen encrusted surfaces face up towards the viewer.  Very quickly, (within an hour), the anthers rotate into their downward facing position.  The flower shown in the two images below is unusual, in that one of the anthers maintained an intermediate position.

One of the three stigmas can be seen in the two images that follow.  Notice the purple spots on the style and the two green pads that form the downward facing stigma.  The off-white ellipsoidal ovary can be seen at the top of the left image.

Two images follow showing the top surface of an anther, and the broad purple-spotted green filament.  The active, pollen covered surface of the elliptically shaped anther is visible around the circumference.

The quantity of bright yellow pollen covering the anther’s surface is so great that it is difficult to see that there are two independent sections to the anther.  (The hybrid passiflora that is discussed in the next section shows this more clearly.)

Under the microscope, (using dark-ground illumination), the remarkable pattern on the surface of pollen grains is clearly visible.  Many of the pollen grains are malformed in any given sample.

The image below shows part of the corona with its double layer, (pali and radii), of multi-hued filaments.  Notice the green “hook” on the structure at the top of the picture that indicates that this is a sepal, and not a petal.

At the center of the flower, there is a strange ring of purplish-brown fibers that sweep up towards the central green column, called the androgynophore (column supporting both male and female organs).  These fibers form part of the operculum, a ring which protects the nectar producing area of the flower.  Insects must penetrate this ring of fibers in order to obtain nectar, and in so doing they come in contact with the pollen encrusted anthers.  Notice in the right-hand image, the ring of tiny sphere-tipped fibers that is located at the starting points of the corona filaments.

Red Passion-Flower Hybrid “Lady Margaret”
Passiflora coccinea x incarnata

The striking structural novelty of Passiflora species has led to many hybrids being developed.  “Lady Margaret”  has smaller flowers than the blue passion-flower, but it makes up for this by its wonderful deep red colouration.  The corona filaments here are thinner and more irregular than those of the blue species.  The dark green leaves of the plant have three lobes.  Notice in the image below, the early stage bud on the left, and the curled tendril in search of a stabilizing branch, beneath the flower.

The image and illustration that follow show the main parts of the flower.  The same structures exist here, however, the colouration is very different.  Note that in some blooms, the three stigmas and styles are less vertical than in this particular flower.

In my opinion, the strangest structures on this passion-flower are not showy at all!  They are the many glands that can be seen as spherical protuberances at the base of the bracts, (modified leaves), that enclose the bud shown below.

A higher magnification reveals these petiole glands.  Only the bracts are visible because the flower has finished blooming, and has dropped off.  The glands secrete a sugary nectar to attract ants which then remain on the plant to digest the eggs and larvae of other insects.  The third image clearly shows tiny, variable sized spherical drops being forced from the glands.

Under the microscope, more detail is resolved.  The drop of nectar in the left image was inadvertently removed during handling.  In the right image, the drop seems to be coated with a translucent film.

The four images below show the opening of a “Lady Margaret” bud.  Notice the small size of the bracts in this species (first and third image).  Also note the three-lobed structure of the leaf in the second image.

The non-reproductive structures of a flower can be seen in the following illustration.

Top and side views of a flower follow.

The three stigma-styles of the plant are particularly sculptural in quality.  If modeled in bronze,  they could happily be displayed in an art museum!

Even a single stigma supported by its style has an elegant simplicity of form. 

The anther and stigma both face downwards in this hybrid, as in the earlier species.

Note the two yellow pollen bands on the bottom of an anther.  This is relatively unusual in flowers.

As a flower opens, the anthers change position until they are facing downwards – away from the active surfaces of the stigmas.  The image below left does not make it apparent as to how this happens.  A different vantage point provides the explanation.  The connection between anther and filament is an extremely thin thread of tissue.  It is gravity that moves the anther into a hanging position.  The thread is so fine that the slightest current of air will cause the anther to swing.

A microscopic view of the point of connection is shown below.

The corona filaments of this hybrid are much finer than those of blue passion-flower.

Near the tips, the filaments are white with irregular red spots.  The photomicrograph on the right shows the red-pigmented cells that form the spots.

The fibers forming the operculum, that protects the nectar forming structure in the flower, can be seen below.

By removing the stalk (androgynophore) holding the reproductive structures, it is easier to see the symmetrical beauty of the fringe of corona filaments.

Passion-flowers are so unusual that they almost look other-worldly.  One wouldn’t be surprised to find them in an alien landscape on an episode of Star Trek!

Photographic Equipment

Most of the photographs in the article were taken with an eight megapixel Canon 20D DSLR and Canon EF 100 mm f 2.8 Macro lens.  An eight megapixel Sony CyberShot DSC-F 828 equipped with achromatic close-up lenses (Nikon 6T, Sony VCL-M3358, and shorter focal length achromat used singly or in combination), was used to take a few images. The lenses screw into the 58 mm filter threads of the camera lens. 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 photomicrographs were taken with a Leitz SM-Pol microscope (using dark-ground condenser), and the Coolpix 4500.  

Additional Information

The 'floral marvel', 'flos passion' or passion flower:


Passion flowers:


Passiflora caerulea:


 All comments to the author Brian Johnston are welcomed.

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