All Lady’s Slipper orchids belong to the Cypripedioideae, a sub-family of the Orchidaceae.  They differ from the rest of the orchids in that they possess two anthers instead of the usual one.  Although in many orchids, one petal forms a landing platform for insects, here it is transformed into an elegant, and very distinctive pouch-shaped insect trap.

The Paphiopedilum genus was established by Ernst Hugo Heinrich Pfitzer in 1886.  Generated using  Paphia, one of the surnames of Aphrodite, and pedilon meaning a sandal, the genus translates to “Aphrodite’s sandal”.  This is in reference to the bulbous pouch which is the orchid’s trademark characteristic.

Paphiopedilums may not have a scent, but they more than make up for this deficiency with their unique structure, and many diverse colourations.  Thousands of hybrids have been produced with a variety of colours including white, yellow, maroon, red, pink and green.  Sepals and petals often have hairs, spots, warts, and stripes which add to the flower’s visual interest – for both humans, and insects!

Many, but not all Paphiopedilums have mottled, or patterned leaves.  The one shown below belongs to the Lady’s Slipper Orchid studied in this article.


Orchids normally have an outer whorl composed of three sepals (modified leaves that protect the flower’s bud stage), and an inner whorl of three petals.  Paphiopedilums however, are different.  The distinctive banner-like structure at the top of the flower is the dorsal sepal.  The other two sepals are smaller, and are fused together to form an apron-shaped structure that is hidden behind the pouch at the flower’s base.


Two of the three petals can be seen as the purple-spotted wings that angle down from the flower’s centre.  The third petal is grotesquely transformed into the flower’s distinctive pouch.


A view from behind shows the synsepal – the apron-shaped structure formed by the fused remaining two sepals.  It hangs down from the point where the flower’s stem-like ovary meets the bloom.  Notice that it too is white with green stripes.


The deformed, slipper-like third petal is called the labellum or lip of the orchid, and as we will see later, it plays an important part in the fertilization process.
 

The colour contrast between the dorsal sepal and the rest of the flower is striking.


The dorsal sepal is composed of translucent cells, and is quite different in substance from that of the petals, which tend to be leathery.  The light green “veins” or “ribs” are raised a considerable distance above the white tissue of the rest of the sepal.


As the magnification is increased, the cellular structure of the sepal becomes easier to resolve.



All three of the flower’s sepals can be seen in the view from the back that follows.  The dorsal sepal points up, while the two lateral sepals are fused into the synsepal, that points down.


The two slightly drooping petals seen on the left and right in the image below, are grooved, and covered by deep purple, wart-like spots.


A closer view of a petal reveals that it has many tiny hairs growing from both the upper, and lower edges.


A petal’s surface is composed of cells which reflect light, and this results in it appearing shiny under some lighting conditions.


Petal warts are very irregular in shape.


Before we look at the reproductive strategy of the Paphiopedilum orchid, a little terminology must be understood.  Both the flower’s male, and female reproductive organs are held at the end of a rod-like structure called the column (or gynostemium), which is an extension of the stem and ovary.  Two fertile anthers are attached to the column, one on either side.  A curiously modified third anther, this one infertile, is located at the end of the column.  Looking somewhat like a shield, it is called the staminode.  Also connected to the column, but hidden behind the staminode, is the flower’s stigma.  The relative positions of all of these reproductive structures can be seen in the diagram that follows.


Since the anthers and stigma are hidden behind the staminode, a visiting insect cannot see them.  In other orchid species, the labellum provides a landing place in close proximity to the reproductive parts - not here however.  While searching for nectar, an insect may fall into the Paphiopedilum’s pouch, and be caught in the trap.  Unfortunately for the insect, the inside of the pouch is lined with shiny, slippery cells – except in one location!  On the interior dorsal wall (the back of the pouch), there exists a ladder made up of tiny hairs that point upwards.  Only here can the insect escape in the same way a wall climber does, by using the projections that are provided for that purpose.  When the insect reaches the top of the labellum, it is very conveniently positioned immediately below one or other of the anthers, and the stigma.


Notice in the two images that follow, how the sides at the back of the labellum curve inwards to produce a vertical tunnel that funnels the climbing insect into the correct position.


The outer surfaces of the folded labellum, (just below the staminode), are covered by reddish warts, and appear particularly shiny.


Close examination of one of these surfaces reveals that it is coated by an appetizing (to insects) liquid.  Since there is no “foothold” for an insect to use while sipping the liquid, this increases the possibility of a fall into the depths of the labellum – the carefully laid trap.


Before I begin to remove parts of the flower in order to provide a better view of the anthers and pistil, take a look at the images below.  The entire labellum will be removed, as well as both petals.


Here’s the result, shown in both front and side views.  Only the dorsal sepal, and fused lateral sepals (synsepal) remain.  The disk-shaped structure immediately beneath the staminode is the flower’s stigma, and its active surface faces down in both images.  The image on the right shows one of the two ball-like anthers attached to the column.


Here is a better view of the staminode, and the upper (non-active) surface of the stigma.


Note the red, nose-like protuberance in the middle of the staminode.  The entire surface of the structure is coated with tiny, downward pointing hairs.


These hairs can be seen more clearly below.  Notice the interesting green pattern on the staminode’s surface.


Each anther is attached to the column by a small horn or “hanger”.  In Paphiopedilums, the pollen is held in a waxy, fairly undefined mass with the consistency of mealy beeswax.  In the images below, this mass of pollen is bright yellow, and a section of a sphere in shape.  The paler yellow material attached to the outermost region of the pollen mass, is called the anther cap.  This sticky, waxy cap is what gets stuck to the leg or body of an insect as it brushes against the structure.  As the insect moves away, it carries the cap, and the attached pollen mass with it – perhaps to the stigma of this flower, or perhaps to the stigma of a nearby flower of the same species.  Self-fertilization would be the result of the first possibility, and cross-fertilization the result of the second.  Of course, cross-fertilization is preferred for the long-term well-being of the species.


Between the plant’s stem, and the flower’s ovary, is a pair of small green leaflets.  Notice that the ovary has a number of longitudinal grooves on its surface.


These grooves can be seen more easily at higher magnifications.


The ovary is coated with a multitude of tiny hairs.


In the wild, orchids often have particular insects that they attract to accomplish fertilization.  Many use bees, while others have pollinator relationships with moths, butterflies, hummingbirds, flies, gnats and bats.  Human orchid growers of course may use a toothpick to transfer the pollen mass to the flower’s stigma.  Although not as exotic, the process is just as effective!


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.

 All comments to the author Brian Johnston are welcomed.