A Close-up View of a Moth Orchid

Southern Ontario winter is not conducive to the collection and photography of wildflowers. As I write this article, the outside temperature hovers at -25 degrees Celsius and the landscape is covered by a thick layer of snow. Fortunately, modern horticulture and transportation services provide us with the tropical blooms of warmer climes at any time of year. The subject of the article was purchased from a large building supply store during a trip to obtain light bulbs. I had been looking for an attractive, healthy orchid for several weeks in garden centres, but strangely, this was the best that I had seen.

The flower of a phalaenopsis orchid resembles a moth in flight, and thus it is understandable that the common name for the plant is “Moth Orchid”. Phalaenopsis originates from the Greek phalaina, meaning “moth” and opsis, meaning “like”. The original phalaenopsis orchids were difficult to grow in the home environment and over the years, intensive cross-fertilization has produced a large number of colourful hybrids that thrive in this environment. According to the information supplied with my plant, two phalaenopsis hybrids, New Glad and Luchia Lady were crossed to produce white flowers with striking red veins and spots.

Although my specimen was grown in a greenhouse in the United States (Florida) and transported to Canada, phalaenopsis orchids are native throughout Southeast Asia, and can be found from the Himalayan mountains to as far south as the Philippines and northern Australia. They tend to grow in the shade below the canopies of moist and humid lowland forests. Most plants have four or five fleshy, dark green leaves. These leaves can be seen in the image below, taken immediately after the orchid was purchased.

As regular readers of my wildflower articles know, I favour a black, rather than natural background for my images, since it increases the contrast and seems to show details more clearly. For comparison, images using both techniques are shown below.

The closer views of a flower in the following images reveal several of the unique characteristics of the orchid family. Blooms consist of three petals and three petal-like sepals (modified leaves). At an early stage, these three sepals form the protective sheath of the unopened bud. In addition, one of the petals is special, being particularly colourful and projecting out towards the viewer. This is called the lip or labellum of the bloom. The positions of the various flower parts are shown in the third , labelled image. It is interesting that as the flower begins to bloom, its stem twists in order that the lip or labellum is positioned at the bottom of the flower when it finally opens. (This process is called resupination.)

From behind, the three sepals are clearly visible. Note how similar their colouration is to the actual petals. By contrast, in most wildflowers, the sepals look more like leaves, and are usually green.

The buds and flowers grow in alternating fashion on both sides of the stem. (The image is taken from below, looking up at the bottom of the flowers.) The brown plant stem tends to be rather tough and woody, whereas the pinkish flower stems are fleshy and more fragile.

The side views below of a phalaenopsis flower show the projecting petal or lip. In resupinate orchids, this more colourful petal helps to attract insect visitors and provides a landing platform when they arrive. This particular species possesses two hook-like appendages on the lip that curve back towards the centre of the bloom.

The labelled image below shows the main parts of the phalaenopsis’ reproductive system. At the centre of the flower is a roughly cylindrical projection called the column. This is actually a continuation of the stem of the flower. This column, (sometimes called the gynandrium), contains the male stamens and female pistil. Covering the end of the column is the anther cap which will be discussed later. For fertilization to take place, an insect must alight onto the lip, climb into the throat and up onto the strangely shaped, red-spotted yellow platform beneath the column.

A closer view reveals that the insect is funnelled into the correct position by the walls formed by two of the three lobes of the “lip” petal. Note that the end of the column looks remarkably like the head of a bird with its downward-pointing “beak”, and two red-edged “eyes”. The “platform” for insects investigating the flower is located conveniently immediately beneath the column.

The two images below show the column viewed from above, and slightly below. In the second image, if you look closely, two round yellow structures are visible beneath the pale white membrane, (the anther cap). These are the two masses of yellow pollen called pollinia.

If all petals and sepals are cut from a flower, leaving only the column and stem, (the cylindrical rod at the bottom of the left image), the main parts of the reproductive system can be seen more clearly. The arrow-head shaped projection is the viscidium, a sticky pad to which the two pollinia are attached. This beak-like extension is sometimes called the rostellum. The bulbous yellow bump above the red “eye” is one of the two pollen masses. If an investigating insect backs out of the flower, the sharp point of the V-shaped viscidium is pulled away from the column. Since it, and the attached pollinia are extremely sticky, the entire cap may become attached to the back of the insect and be carried away to another flower. Individual pollen grains are not transported from flower to flower – it is the entire package that is transferred.

The two images below show just what is carried away by a visiting insect. Although it may look as though the tweezers’ tips are holding the anther cap in position, this is misleading. The “glue” on the viscidium and pollinia is so strong that the cap is very firmly held in place without the second arm of the tweezers being in contact. In fact, when the photographs were finally taken, it was very difficult to dislodge the cap, even with the aid of a tissue. (Someone should patent the glue!)

The microscope provides a closer look at the two pollinia.

At a slightly higher magnification, the filament holding one of the pollinia to the viscidium is visible.

The surface of the pollinia is very bumpy as can be seen below.

An insect’s view looking straight up at the underside of the column is shown below. The stigma, (the “cave” of shiny material beneath the “beak”), is the female part of the flower. A thin membrane beneath the anther cap prevents self-pollination.

After an insect strips off the anther cap, two “teeth” called denticulae are visible. These strip the pollen masses from the back of a visiting insect, and perhaps hold the pollinia in contact with the stigma’s surface to enable fertilization.

A closer view of the “platform” beneath the column reveals its intricate shape.

Hook-like appendages at the very tip of the flower’s lip can be seen below. It seems that these structures serve no purpose, and are simply ornamental.

The buds of a phalaenopsis orchid plant slowly increase in size over the blooming period. The flowers bloom in sequence out towards the tip of the stem. Several buds at various stages of development can be seen below.

Red “veins” on the surface of the sepals which form the protective envelope for the developing flower, can be seen in the second image below.

A sequence of four images shows the opening of a bud. The photographs were taken over an eight hour period.

Branching red veins cover most of the surface of both sepals and petals.

Within the throat of the tri-lobed specialized petal, there are red spots as well as the veins that cover all petals and sepals. The photomicrograph on the right shows the structure of some of these cells. The darker nucleus is visible in most.

At a much higher magnification, the protuberances that exist at the edge of a petal are conspicuous.

Individual cells are also resolved in the three photomicrographs below showing areas of the membrane separating the pollinia from the stigma. It is this membrane that prevents self-pollination in the phalaenopsis flower.

Unlike the seeds of most plants, orchid seeds have no endosperm (stored food). In the wild, a symbiotic relationship between the plant and a type of fungus provides nutrition for the growing seeds. This relationship is called a mycorrhiza and derives from the term “fungus root”. The mycorrhiza provides the sugars and carbohydrates necessary for seed growth when the fungus invades the developing embryo. The seed capsules that form may contain from 1 000 to 1 000 000 dust-like seeds.

Phalaenopsis orchids are the most widely grown for the home environment. Their blooms are often strikingly colourful and remarkably long lasting. Even someone like myself, without even a hint of a “green thumb” can keep them alive and blooming for a month or two!

Photographic Equipment

The photographs in the article were taken with an eight megapixel Sony CyberShot DSC-F 828 equipped with achromatic close-up lenses (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. (These produce a magnification of from 0.5X to 10X for a 4x6 inch image.) 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 magnification here is about 14X for a 4x6 inch image.) The photomicrographs were taken with a Leitz SM-Pol microscope (using a dark ground condenser), and the Coolpix 4500.

Further Information

Several web-sites providing interesting information about orchids are listed below.

Phalaenopsis – From Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Phalaenopsis)

Brooklin Botanic Garden (http://www.bbg.org/gar2/topics/indoor/handbooks/bestorchids/11.html#bio)

Linda’s Orchid Page (http://www.orchidlady.com/index.html)

Botany.com – Orchid (http://www.botany.com/orchidaceae.html)

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