Clear Mountain Garden Treasures
 

Clear Mountain Garden TreasuresThe Weird and Wonderful World of Orchids

Weird and Wonderful Orchids

The orchid is a very diverse family of plants that are found on every continent except for Antartica. It is estimated that there are between 20000 to 30000 species of orchids, and at the present, there are over 100000 registered man made hybrids. Orchids range from tropical tree dwellers (epiphytes) with large showy flowers to tiny hardy souls, eeking out a living on rocks (lithophytes) near high, wind swept, mountain peaks. There are orchids that grow on mangrove trees, and even ones that grow on tiny twigs. There are those that grow in the ground (terestrial), in swamps and on river banks.


NZ native orchid: Earina mucronata

The very name, orchids, often conjures up a mental picture of exotic plants, and while this is true for the majority of orchids, little is known that there are quite a number of species that occur here in New Zealand. In fact, New Zealand has around 150 species, and the Waitakere ranges alone have around 50! So lets begin our journey into the facinating lives of orchids, starting from here in our own backyard.

What is an Orchid?
Parasite
Trap doors, a good shot and mimicry
A really long tongue
Weather Station
Blotting paper
Water Orchid
Plain Vanilla
Summary

 What is an Orchid?


Typical flower pollen.

Orchid lip and column.

Orchids are highly evolved and specialised plants. Most flowering plants produce powdery pollen that are either insect- or wind-borned. Most orchids, on the other hand, produce their pollen in tight little bunches, called pollinarium (plural, pollina). They are almost exclusively insect pollinated. The pollina is found at the end of a structure unique to orchids, called the column. A fleshy structure, called the pollen cap, protects the pollina. This can be seen in the photo on the left. The column is red on top and white with red spots at the bottom. The pollen cap is the cream coloured bit at the end of the column. Behind the pollen is the stigmatic surface.


Zygomorphic orchid

Dutch Iris.

Orchid flowers are also zygomorphic, meaning, they are symmetrical only on one plane. The flower in the photo on the right is symmetrical only on the red vertical line. Each flower has six segments, comprising of three sepals, two petals and a labellum (or lip). The labellum is actually a highly modified petal. If it wasn't for the lip, the flower would be symmetrical on three planes, for example, the iris below.

Flowering plants are classified into two groups, monocotyledon and dicotyledon. Monocots have one seed leaf and dicots have two. Orchids are classified as monocots, and like most monocots, their flowers have segments in multiple of three. Their leaves have parallel veins that run for the length of the leaf. However, this is where the similarity ends.


Orchid Seed Pod

Tiny Orchid Seeds

Most seeds have some form of food storage. For most dicots, the cotyledons are the food storage organs, for example, take a look at a pea. One can split a pea nicely into two halves, each half is a seed leaf. Monocots seeds, such as corn, tend to store food in an organ called the endosperm. When a pollen grain germinates, it will grow a tube down to the ovaries. Two sperm cells then travel down this tube. One will fuse with the egg to form the embryo and the other will grow into the endosperm. That is why the quality of corn is determined mostly by the pollinator. This food store feeds the seed when it germinates.

Orchid seeds on the other hand lack any significant food store. They are microscopic, and can best be described as a bunch of a few embryonic cells. They are also produced in abundance, up to a million seeds in a large seed pod. When the seed pod ripens, it dries and splits, releasing the seeds into the wind.

For an orchid seed to germinate, it not only needs to land in a suitable spot, it also needs to be infected by a fungus.

 Parasite

Most orchid enthusiasts will spend a lifetime trying to explain that epiphytic orchids only grow on trees. They do not depend on the tree for nutrients and therefore are not parasites. And they would be right ... most of the time. All orchids have to be a parasite at some stage of their lives.

The tiny orchid seed parasitise fungus to obtain nutrients in order for it to grow. This fungus, known as micorrhizal fungus (meaning root fungus), feeds the seed, enabling it to germinate and grow into a spherical blob of green cells (called a protocorm). Out of the protocom, leaves and roots will then appear. This fungus will feed the orchid until the plant can grow on its own. Each orchid species normally only associates with its own species of fungus.


Orchid seedlings

Orchid seeds are germinated in the lab using sterile conditions. The seeds are sown onto a mix of agar (seaweed jelly) and nutrients and sealed inside a flask. The flask is placed somewhere bright, and temperature controlled. Within weeks, little protocorms will have grown. These are then transferred to other sterile flasks to grow on.

Most orchid species only require the fungi for germination and lose the association once they are able to grow on their own. There is one group of orchids, however, that carry this association further. Most of them are terestrial (lives in the ground) and continue to feed off the fungus throughout their lives. The fungus gets little or nothing back in return, and the association seems to be controlled solely by the orchid. What is more, species of fungi that are highly highly virulent parasites of plants, are themselves parasitised by orchids. These orchids are a parasite's parasite!

A few species even depend solely on the fungi for their existence. They have no chlorophyl and therefore are unable to manufacture their own food from the sun. They live completely underground and exist as tubers. When the time is right, they will produce a flower spike which then reveals their existence. Some species even flower underground!

 Trap doors, a good shot and mimicry


Cycnoches warscewiczii

Orchids employ a variety of techniques to entice insects to pollinate their flowers. Most offer nectar, some have fragrance, but a few species take things to the extreme. Take for example the New Zealand native Pterostylis. It has a hinged lip. When an insect lands on the flower, the lip flips backwards like a trap door, forming a tube. To escape the insect must crawl out through the tube removing the pollina in the process.

Cycnoches and Catasetum have dimorphic flowers, meaning the male and female flowers look very different. They are usually found on separate flower spikes. Each plant can produce either male or female flowers, some years producing male only and other years female only flowers, rarely both. They are pollinated by male euglossine bees that will first visit the more attractive male flowers to obtain a perfume oil that is located on the lip. In Cycnoches, the lip bends down under the weight of the bee causing the back of the bee to touch the pollinia. Male Catasetum flowers are more dramatic. When a bee touches a sensitive trigger on the flower, the pollina are shot at a great speed at the bee. Not only does this stick the pollinia onto the bee, it knocks it for six. The dazed bee having learnt not to visit male flowers then visits the female flower (recap: the female flowers look different from the male), pollinating it.

Other orchids do not produce food or oils for their insect pollinators, but attract them through mimicry. They either look like other flowers that grow in the same vacinity, or their perfume resemble those flowers. Insects visit the flowers but instead of finding a tasty treat, they are burdened by the pollen.

The ultimate in deception must be the bee / fly orchids, Ophrys and Trichoceros They are so named because the resemble an insect and produce a similar pheromone to the female. This pheromone attracts male insects, which then tries to mate with the flower, but only succeeds in collecting pollen. He then flies off and tries to mate with another flower, pollinating it.

 A really long tongue


Angraecum sesquipedale, note
the long spur.

One of the weirdest relationship between flower and pollinator has to be between Angraecum and the hawk moth. They are both found in Madagascar, an island that has been separated from the mainland for many millions of years. Angraecum sesquipedale flowers have spurs up to 30cm long (a foot long!), and the nectar is only found in the last cm or so at the end of the spur. The 19th century naturalist, Charles Darwin, predicted then that there would be a moth with a foot long mouth that could reach the nectar, and hence pollinates the orchid. In his time, Darwin was ridiculed for proposing this idea, and it wasn't until the early twentieth century that a giant hawk moth fitting Darwin's description was found. This moth was named Xanthopan morganii praedicta, in honour of the fact that its existence was predicted.

 Weather Station


Dendrobium crumenatum
Flowers in response to
a drop in temperature.

Epiphytic orchids are very dependent on rain and mist for moisture. As a result, those that live in areas of seasonal rain tend to alter their lifestyle to suit the weather. For example orchids that live in deciduous monsoon forest also tend to be deciduous. Most of the growth is during the monsoon season and they become dormant during the dry season. They flower just before the start of the monsoon, ensuring that the seeds have a chance grow during the wet season.

Some orchids take this one step further. They have a built in thermometer that detects a period of temperature drop. This co-incides with the start of the rainy season. This trigger flower buds on mature canes to start flowering, 9 days after the drop of temperature is detected. As a matter of fact, the timing is so accurate, that in cultivation, it is possible to get these plants to flower on specific days just by moving them to a colder spot.

Recent research also suggests that some of these orchids can detect a drop in barometric pressure, in addition to temperature. Barometric pressure is often associated with weather patterns, and a drop in pressure usually signifies thunder storms. These orchids are essentially biological weather stations.

 Blotting paper


Dry roots


Wet roots

Living high up in the trees poses other challenges. Water from rain is often fleeting, disappearing soon after the rain stops. This means epiphytes only have a short window of time to absorb rain water. However, living plants require constant supply of water. To cope with the drought, Orchids employ water storage organs. These are usually in the form of pseudobulbs - swollen stems, designed to store water and food. Sometimes water is stored in thick leaves. Thick leathery leaves also reduces water loss through transpiration.

To further cope with the drought, roots can also be modified to store water. Most orchids have a spongy layer (Velamen) around their roots that act like blotting paper. This layer is designed to rapidly absorb rain water, and have it available to the roots over a long period. When dry, the velamen keeps a layer of air that insulates the roots from drying out.

Having a velamen is a two edged sword. When wet, the root is not able to breathe. To overcome this, the velamen has areas that do not get wet (pneumathodes). These allow the root to breathe for the short time that the velamen is wet. Roots will still suffocate and die if left exposed to extended wet periods.

 Water Orchid


Disa Alec Lurie

On the other end of the scale, a few species of the genus Disa live amongst reeds on the banks of mountain stream in South Africa. These are water orchids. They spend all their lives with their roots constantly wet. In the summer, they produce a long inflorence (up to 1m long) that carries mainly bright red flowers. While most red coloured flowers are bird pollinated, unusually, Disa flowers are pollinated by a butterfly, the large Mountain Price butterfly.

 Plain Vanilla

The only orchid of commerce is vanilla. It is a large climbing orchid that grows in the warm humid tropics. Vanilla essence that is used to flavour ice creams and cakes, is actually an extract from the seed pod of the this orchid. The flowers have to be hand pollinated to set seed. The pods are picked just before they split. They are cured then dried to preserve the essence.

Another orchid that smells of vanilla is Dendrochilum glumaceum. It produces masses of tiny cream coloured flowers on two ranks along long inflorances. The flowers have a vanilla fragrance.

 Summary

There is so much diversity in orchids that there more interesting plants that are yet to be discovered. Orchids are disappearing fast from the wild, through the loss of habitat and through over collection. Unfortunately, there will be plants that will have gone extinct even before they are discovered. You can stop this decline through two simple steps: Only buy plants from orchid nurseries that guarantee plants are nursery grown. Only buy furniture from brands that guarantee the wood is sourced from renewalable forests. I hope you have enjoyed this trip in the world of orchids.


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