The peak of flower evolution

Nov 17, 2007 09:02 GMT  ·  By

You may not like flowers, but if you like vanilla, you actually like ... orchids. Vanilla is the only comestible orchid and the vanilla stick is nothing else than the fermented and blackened pod of an orchid, Vanilla planifolia that is to be found in Mexico. (in fact "vanilla" means "little pod" in Spanish).

Did you know that the name "orchid" comes from the Greek "orchis" (testicle), due to the shape of the tubers in some species? (avocado for example means "testicle" in the Aztec language because of its shape). There are up to 35,000 species of orchids in the world: about one eight of the flower plants in the world, a peak of the co-evolution between plants and insects.

The lower part of the three petals of an orchid is reverberated and works as a landing platform for insects, being more developed, longer or wider and often crispy. It often has a more vivid color, being different than the rest of the flower. The orchid forms a nectariferous spur for attracting pollinating insects. Orchids also evolved a bent anther (the pollen-producing flower part) which ensures that the sticky pollen clump gets stuck on the back of the visiting insects. The complex structure of the orchid flower ensures that the visiting insects get a load of pollen packages. The largest orchid flowers are those of Cattleya: up to 30 cm (1 ft) long.

One issue: hummingbirds are not attracted by orchids! They cannot effectuate the orchids' pollination.

Recently, it was found that orchids are one of the oldest plant families, dating from the dinosaur era. An amber encased stingless bee (Proplebeia dominicana) carrying a clump of orchid pollen on its back and 76 to 84 million years old was found in Haiti. Dinosaurs disappeared 65 million years ago. The location and shape of the pollen clump permitted the classification of the ancient orchid, named Meliorchis caribea, within one of five living lineages of orchids. The genus Vanilla (from which vanilla is obtained) was found to be 60-70 million years old, based on the molecular clock.

Orchids grow in many areas, from the wet tropical forests to swamps, deserts, alpine pastures and rocks or polar tundras, still most species are found in wet tropics, the richest orchid areas being the mountains and plains of north South America- Central America and southeastern Asia to Himalaya. The national flower of Venezuela is the orchid Cattleya mossiae, which grows in the Venezuelan Andes at heights of 1,000-1,700 m (3,300-5,600 ft) and flowers in May, that's why it is called Flor de Mayo (May Flower in Spanish).

Orchids need light, that's why many tropical orchids are epiphyte over the trees' branches (used just as props) or rocks, fluttering their roots in the air while others open their flowers underground, without seeing sunlight. In temperate zones, orchids are terrestrial plants.

The shape of the orchids' flowers is extremely varied: some imitate bees or butterflies; other can look like lizards, frogs, or a miniature human being...

In southern Europe and Mediterranean area, drones looking for a mate can be fooled by a bee orchid from the genus Ophrys. These orchids do not have attractive nectar, so they fool the drones by mimicking the looks and scent of a bee queen. The drones will attempt to mate with bee orchids but before they become aware of the mistake, the orchid has already deposited a pollen package on their body. The drone flies off and when he gets fooled again, he has delivered the pollen to another orchid. After a few deceptions the drone realizes the trick, but he may have already pollinated several orchids. Each species of Ophrys orchid has its own pattern and smell, and also imitates wasps and bumble bees.

An Australian orchid has various hairs that make it look like a caterpillar. Attracted by the "prey", wasps sting it for laying their eggs and when they fly off, they already got a pollen load.

Habenaria blephariglottis from North America is called "monkey face", the Cycnoches from Central America are named "the swan orchids" because they look like a swan's neck. Oncidium from tropical America is called torrito ("little bull" in Spanish) because it has two little "horns". Cypripedium from northern temperate zone is called "lady slippers", for obvious reasons.

A Guatemala orchid has a "landing platform" that looks by itself like a flower but it does not offer nectar.

One of the rarest and most mysterious orchids in the world is the ghost orchid (Polyrrhiza lindenii) which is also called Palm Polly and White Frog Orchid. The endangered epiphyte flower grows about 45 feet (15 m) off the ground, anchored in a network of large, tangled mass. The species inhabits moist, swampy forests in southwestern Florida, the Bahamas and Cuba. As the roots of this orchid blend so well with the tree, the hand-sized flower often seems like it is floating in midair, that's why it is called "Ghost Orchid".

This orchid lacks a stem and the leaves have been reduced to scales; it is made of only flat, cord-like, green roots that absorb moisture and make photosynthesis. Pollination is possible due to the giant sphinx moth, the only local insect with a long enough proboscis to be able to do this.

The smallest orchid plants are no taller than 6 mm, while the largest orchid can be a 30 m (100 ft) long vine. Orchids expel perfume only during specific periods of the day or night, linked to the activity of their pollinators and the weather, to which these plants are very sensitive. Some orchids in fact stink, like dung for example, attracting pollinating beetles, like the bog-orchid (Platanthera) of the Rocky Mountains.

Orchids have the smallest and most numerous seeds amongst flowering plants. A seed weighs 3-14 micrograms and a sole capsule of Cycnodies ventricosum up to four million seeds! If all seeds of an European orchid germinated, the Earth would be covered in orchids for three generations.

But till the beginning of the 20th century, orchids could not be cultivated from seeds. Orchids for collections in greenhouses had to be brought alive from the tropics. In 1904 a French researcher found that orchid germination required a specific fungus.

Unlike other seeds, the orchid ones do not contain nutritive compounds and their development is linked to a microscopical fungus that invades them supplying the little seeds with food, by degrading starch to glucose.

Currently orchids are bred mostly by meristem (embryonic tissue) cultures. From the orchid's bulb meristems are extracted and cultivated till the achievement of clone mature plants. In Thailand, over 100 species are regularly cultivated. Artificial breeding is a way to save many wild orchids, savagely pillaged from nature. About 20 % of the total of 5 billion annually traded orchids come from the wild.

Orchids have medicinal uses. In the Amboina Island (Indonesia) a paste made of Grammatophyllum is used against pains and in Malaya Dendrobium fights skin infections. In South Africa, Zulu use Habenaria and Swazi the Lissochilus genera. The tribes of Amazon believe that the flowers of Epidendrum bifidum, Spiranthes protect people from diseases.

Vanilla is the only food orchid, being cultivated even from Aztec times. Even if today half of the world's production comes from Madagascar, the plant must be pollinated manually there as no local insect is adapted to it!

Darwin found in the 19th century in Madagascar an odd orchid, baptized Angraecum sesquipedale. The nectar glands were located in the end of a tube 35 cm (14 inch) long. Darwin forecast it must have been a butterfly with a trunk. 40 years later, the Xanthopan moth was found: it had a trunk over 30 cm (12 in) long!

Orchids depend on insects for pollination and when the habitats are modified, insects die or move, dooming the orchids.

Photo Gallery (4 Images)

Bee orchid (Ophrys apifera)
Cattleya rex from northern AndesCypripedium calceolus from Europe
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