The Orchid and It’s Structure

Typical shapes of growth

Orchids grow in two ways. They either extend their shoot tips, growing monopodially, or branch out laterally, growing sympodially. In monopodial growth, the new leaves always appear at the tip of the main axis. The plant seems to grow taller every year. The flowers appear along the main axis. There are no pseudo-bulbs. Typical of this group are Vanda, Phalaenopsis and Paphiopedilum.

In sympodial growth, the main axis is not upright but prostrate. New shoots grow laterally from the base of the previous year’s shoot (as in Iris species) and will eventually grow over the edge of the pot. Sympodial orchids form pseudo-bulbs and the flowers appear at the ends or along the sides. Typical examples are Cattleya and Cymbidium.

 

Pseudo-bulbs

orchid and it's structure Many sympodial orchids produce conspicuous, peculiarly shaped lumps from which the leaves grow. These are thickened shoots which serve as storage organs for water and nutrients, hence the name pseudo-bulbs or simply bulbs (from Latin: bulbus = bulb). Their function is to help the orchid to survive periods of drought. These bulbs come in many different shapes: cylindrical, spindle-shaped, egg-shaped, spherical, barrel-shaped and flattened. All the pseudo-bulbs of an orchid are connected to each other by a main axis. Every year, a new, fat, smooth bulb develops and produces leaves. The old bulb becomes wrinkled and loses its leaves but continues to supply the younger bulb with nourishment.

 

Terrestrial and aerial roots

As in all plants, the roots of orchids are responsible for the supply and transport of water and nutrients. This is not their only purpose, however. Species that live on trees or on steep rock faces also use their roots for holding on. In this way they are able to anchor themselves so securely that it is very difficult to remove them.

Terrestrial roots are found on terrestrial orchids. In tropical species these roots are generally thick, but they are thinner in European species, generally do not branch out and are often quite hairy.

Aerial roots are found on epiphytic and lithophytic orchids. These roots are thick and fleshy. They are firmly rooted in soil, grip tightly to a base or dangle free in the air. Aerial roots look a lot like worms, snakes or ribbons, contain chlorophyll and are able to aid the orchid’s leaves in the process of photoynthesis. A special feature of these roots is their silvery skin, called velamen. This skin consists of empty, air-filled cells which suck up and store moisture and nutrients, It also functions as insulation against ultraviolet radiation and drying heat.

 

The structure of a shoot

Orchids grow monopodially or sympodially. Monopodial growth is distinguishable by the non-branching vertical shoot, from which leaves and flowers grow laterally. Sympodial orchids have a horizontal axis and pseudo-bulbs.

 

Orchid leaves

Even more than the flowers, it is a study of the leaves and pseudo-bulbs which supplies information on the care a particular orchid requires. In addition, you can tell by the leaves that orchids belong to the monocotyledon group of plants. Like palms, grasses and lilies, nearly all orchids possess smooth-edged leaves with veins running parallel. Divided leaves or leaves with web-like veins are very rare. Orchid leaves may be minute or more than a metre (3 ft) across, and shaped like scales or tubes. There are broad leaves and very narrow ones, paper-thin ones and fleshy, thick ones, hard and soft ones. In some orchid species the leaves last for many years, in others they fall after one growing season.

The colour of the leaves provides information on where the plant originates. Dark green leaves generally indicate a position with poor light; fresh green leaves a position with normal lighting; grey green ones a position with an abundance of light. Many orchids possess striped leaves or leaves with a checkered pattern — some even have leaves that look like brown or green velvet shot with silver or gold threads. In these species, the flower will be small and inconspicuous, unlike the majority of orchids, in which the flower is the most spectacular part of the whole plant.

 

The orchid flower

Orchid flowers appear in a confusing multitude of shapes, colours, patterns, structures and scents. One can find flowers that are no larger than pinheads and others that extend to a metre or more across (over 3 ft) if you include the length of petals that grow into long points. Some species form single flowers, others form inflorescences with two to countless flowers, while others, again, produce thick racemes or upright spikes. The range of colours is enormous; only blue is fairly rare. Very often, individual petals appear in different colours or decorated with spots, stripes or a marbled effect.

 

Scented orchids

Odontoglossum cirrhosum - scented orchids A number of orchids have developed the production of scent to a fine art in order to tempt pollinating insects. Astonishingly, some orchids are even able to change their scent depending on the customers they hope to attract at different times of the day. For example, Phalaenopsis smells of lily-of-the-valley during the daytime and of roses during the night. One Dendrobium species disperses the vanilla-like scent of heliotrope early in the morning and the scent of lilac during night-time hours. Other orchids imitate the scent of gardenias, hyacinths, stocks, primroses or jasmine. Some of the real masters among the fragrant orchids manage to produce the scent of spices, honey, fruits or leather.

For example, Odontoglossum cirrhosum, Odontoglossum pendulum, Cattleya citrina and Epidendrum fragrans smell of lemons. The scent of pineapple can be found in Aerangis crispum. Vandopsis smells of leather; MaxiIlaria picta of honey. Lycaste aromatica and Epidendrum radicans carry the scent of spicy cinnamon, Odontoglossum ornithorhynchum and Angraecum fragrans smell of vanilla, while Oncidium lanceanum smells of cloves.

Of course, orchids do not produce their scent in order to please us but to attract pollinating insects, so there are also species which smell of mothballs or rotting meat!

 

The structure of the flower

In appearance an orchid flower appears complicated and yet it is sophisticatedly simple. Most orchid flowers consist of six, coloured petals arranged symmetrically on two sides. The flower consists of:

  • three outer sepals (which have grown together in some species)
  • two inner petals
  • a conspicuously shaped and coloured lip (labellum) which is really a third, metamorphosed petal. The labellum is generally shaped like a small pouch or shoe in flowers with two fertile stamens, for example in lady’s slipper orchids: in flowers with one fertile stamen it is shaped like a funnel or pipe, or is even flat with three lobes
  • the columna, a finger-like structure in the centre of the flower, which bears male and female parts. By contrast with other flowering plants in which the stamens and stigma are distinctly separate, these have usually fused in orchids. The anther, with its male pollen grains, is usually placed at the top of the tip of the columna, and the surface of the female stigma is on the underside of the front of the columna.

Pollination and seed formation

The colour, scent and structure of the flower serve purely to ensure the propagation of the species. Orchids are mainly pollinated by insects — a very few by snails, bats or hummingbirds. Every flower is not only perfectly adapted to its particular pollinator, it is also constructed in such a way that auto-pollination and self-pollination are avoided.

Very often the flower lip bears a deceptive resemblance to the female partner of a pollinating insect and will also smell the same. After successful pollination, the petals wither and the ovary begins to swell, then ripens and forms a seed capsule. The capsule contains thousands of powder-like seeds, the very smallest and lightest of all flowering plants. Two or three seeds weigh about a millionth of a gram. In Anguola ruckeri up to three and a half million seeds are contained in a capsule the size of a walnut! As soon as the seed is fully ripe — which often takes months — the capsule splits open along its seams.

 

Flower-producing shoots

Flower-producing shoots appear on various different parts of the plant, depending on the species. In Paphiopedilum they emerge from the centre of the leaves which are themselves divided in two parts and grow one inside the other. In Vanda and Phalaenopsis the flowers form along the sides of the stem at an angle of about 90 degrees to the leaves. In Dendrobium they appear on the upper part of the plant. In Cattleya and Laelia the flower emerges from the tip of the bulb, and in Oncidium, Odontoglossum, Coelogyne and Miltonia it appears laterally from the base of the bulb.

 

Are there any toxic orchids?

Orchids are not listed in most standard works on toxic plants. However, this does not mean that orchids do not produce any toxins at all as this subject has not yet been fully investigated scientifically. For this reason, we recommend that you take great care that children and domestic pets cannot gain access to your orchids. Some orchid scents can cause headaches in sensitive individuals. If you know that you react adversely to scents, you should never keep highly scented orchids in a bedroom. There have also been cases of skin infection caused by contact with the very hairy leaves of Cypripedium pubescens. Make sure that you wear gloves every time you handle hairy orchids.

08. December 2010 by admin
Categories: House Plants, Orchids, Orchids, Plants | Tags: , , , | Comments Off on The Orchid and It’s Structure

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