Orchids are one of the most interesting plants with the most fascinating life cycle, which is similar to most flowering plants but with a number of twists. They have, for example, developed odd pollination strategies with some orchids producing the pheromones of female wasps to attract the male wasps who then pollinate the flowers! Some orchids also have the capacity for self-pollination. In this section we'll look at the fascinating aspects of the orchid life cycle and the orchid reproduction cycle. We'll also look at the different habitats that the orchid plant can grow in.
The Orchid growth habit
All orchids conform to either a sympodial or monopodial growth habit.
Orchids with sympodial growth habits refer to those orchid plants in which the new growth comes from a lateral shoot. Orchids with monopodial growth habits refer to those orchid plants which have a stem that grows annually from the apex.
Most of the known orchid species exhibit sympodial growth habits. With this growth habit the orchid produces a thick bulb-like structure also known as pseudobulbs. These pseudobulbs store moisture and nutrients for the orchid and usually grow along the rhizome. Of the most well-known species of orchids that has sympodial growth habits are the Cymbidium orchids which have pseudobulbs that appear almost to grow in a bunch because the rhizome acts as a very short thread that seems to connect the pseudobulbs. The other examples are the Bulbophylum orchids which has pseudobulbs that grow approximately 3 to 4 cm (i.e. 1 ½ to 2 inches) apart on the rhizome.
The orchid leaves, flower stems and flowers itself develop from the new growth from the pseudobulb. The new growth will appear from the bulb, fresh leaves will emerge and a new bulb will form along the rhizome. After it fulfilled its duty of supporting the new growth, the existing pseudobulb will go dormant and become a back bulb. In the back bulb phase the new growth will continue to exploit the last energy resources stored in the back bulb until the back bulb is depleted. The back bulb will then only shrivel up and die.
Not all sympodial orchids develop pseudobulbs. Many species of Paphiopedilum orchids will grow stout shoots from the base of the plant. This is especially true of the Paphiopedilum species that grows in areas of high humidity. As the leaves and shoots die, new growth will appear from the existing base. The thick and fleshy roots will hold all the required moisture reserves.
Contrary to sympodial growth the monopodial growth habit orchids grow vertically and get reach incredible heights. There are some Vanda orchid species that grew several meters tall. Monopodial orchids do not form pseudobulbs. The new growth will form from the end bud of an old shoot, and leaves and flowers are then produced along the new stem. Also due to the lack of pseudobulbs, the new growth is supported by succulent leaves that store the nutrients and moisture required for the new growth.
Orchids can grow in a variety of habitats: marshes and wetlands, on trees, in the ground, on piles of decaying organic matter, etc. and they can be divided into three main groups namely: epiphytes, lithophytes and terrestrial. Orchids can also interchange their habitat depending on the circumstances it finds itself in. e.g. a terrestrial orchid plant that grows near the base of a tree might grow further and grow on the trunk of the tree becoming epiphytic. Some orchids will even grow on rocks if the opportunity arises and there is enough moisture and nutrients to sustain its growth.
Most species of orchids, including some of the most beautiful specimens, are epiphytic and grow in subtropical and tropical areas. They grow on host trees supported by the trunks and the thick lower branches of the host. Sometimes they are perched on small twigs in the very top of the canopy of the trees. All epiphytes cling to their hosts with very strongly developed root systems. These roots take advantage of the moisture and organic debris that are caught in the crevices and bark of the host for nourishment purposes. All additional moisture and nutrients that are required are absorbed from the humid tropical air. This in itself spells out the importance of air movement for the epiphytic orchids.
Epiphytic orchids also take advantage of the microclimates offered by their hosts. Some epiphytic orchids prefer shade or moderate dappled light and will prefer to grow on the trunk or lower branches of the host tree while other that require direct sunlight and ventilation will prefer the canopy at the top of the host tree. Most notable species of orchids that are epiphytic are Oncidium orchids, Miltonia orchids and Cattleya orchids.
These orchids have the ability to adapt to growing conditions that are quire varied: from boggy ravines to damp forest floors, from sandy dunes to semi-arid desert soil. The terrestrial orchid roots produce tubers that may lie just below the soil surface and some even deep underground depending on the circumstances. They store their nutrients and moisture in these tubers that will see the plant through those periods of total dryness in some cases. Often you will find that terrestrial orchids are deciduous in that their flowers and leaves fade in winter and remain underground until the new growth season begins. New growth will then appear as a single leafy stem topped by flowers. The terrestrial orchid sometimes occurs in singular plant form and sometimes in clumps amounting to several hundred individual plants. Examples of semi-terrestrial orchids include Cymbidium orchids, Paphiopedilum orchids and Calanthe orchids. Examples of true terrestrial orchids are Stenoglottis, Disa uniflora, Bartholina and Satyrium which all have underground tubers and/or rhizomes.
The lithophytic orchids are mainly found in the tropical regions of the world. They grow on the exposed rocks and sometimes even make their habitat on high outcrops. They have strong roots that absorb moisture and nutrients from the air and all additional supplies that are required are harvested from the rock crevices amongst the moss the organic debris that collects in these crevices. More often you will find that the leaves of lithophytic orchids are quite fleshy, and the pseudobulbs would also be succulent to carry the plant through prolonged dry spells that might occur.
The Orchid Life Cycle
The life cycle of an orchid is much like the ordinary conventional flower: Seed production, Germination, Seedlings, Maturation of seedlings into plants, Flowering and Reproduction and seed production.
The first part of the orchid life cycle is the act of pollination that sets into motion a chemical reaction. The consequence of this chemical reaction is a signal for the orchid to start the orchid reproduction cycle. The first visible sign of the orchid reproduction cycle is the wilting of the orchid flower – the sepals and petals start to shrivel and die. This sound rather like any other conventional plant doesn't it. But orchids have very extraordinary differences in their life cycle. The flowering period after pollination varies significantly and some orchids may even take anywhere from nine (9) to fourteen (14) months to complete a full life cycle.
Amongst all the features, prolific seed formation is common in all types of orchids. What is peculiar however is that, depending on the orchid species, the seeds can take quite some time to mature. In Cymbidium orchids and Cattleya orchids the seeds take up to twelve (12) months to mature.
Most orchid species are epiphytic and this means that certain adaptations to their habitat must be adhered to so to ensure survival of the species in nature. A heavy seed for instance will drop, fall from the tree and land on the ground. NOT good since it is an epiphytic orchid. Instead the adaptation here would be feather-light, small, delicate seeds which can easily be airborne and will then stand a better chance of landing on a hospitable spot.
Terrestrial orchids on the other hand have specific soil requirements and their adaptation to their natural habitat would be to disperse a copious amount of seed as it will increase the species' chances of survival in terms of propagation. This will almost seem like a waste, but of the copious amounts of seeds produced and dispersed only a small percentage actually land in a suitable environment for growing.
Where orchid plants also differ significantly from conventional flowering plants, is that its seed lacks endosperm. Orchid seeds need a fungus for germination purposes. The fungus takes on the role of the endosperm of providing the required energy. This specific fungus that orchid species require to complete the orchid reproduction cycle is the mycorrhiza fungus.
Form, fragrance and function in the orchid reproduction cycle
Many orchid flowers have fragrances that it emits. However, the fragrance of the orchid flower can range from wonderfully sweet odors with a hint of chocolate and even musk right through the spectrum to stinky, putrid and acrid smelly fragrances. Within this wide range of orchid fragrances, the idea is to attract specific types of pollinators. These fragrances are produced by special glands that can be found on the lip of the orchid flower.
Due to the different photo-sensitive and activity levels of the different pollinating agents, the orchid also adapts it fragrance release apart from the usual floral color. It would be a waste of energy if the orchid flower is meant to attract bees and produce its fragrance right through the day since bees are most active in the morning. You will thus find that this specific orchid that requires bees as pollinating agents is fragrance-free at night.
On the opposite end you get types of orchids that depend on moths as their pollinating agents. During the day the orchid flower will be relatively fragrant-free, but will intensify the fragrance at night when moths are active. Most insects that are acting as pollinating agents are usually short-sighted, some with a specialized sense of vision. Scent and fragrance is thus ideal to lure them.
Some orchid species even mimics the pollinating agents that they want to attract. Some orchid species even exhibits an intricate combination of fragrance; color; and structure that are meant to mimic and entice specific pollinating agents. The most spectacular example of all three adaptations that warrants a special mention here is the Ophrys sphegodes. This orchid is amazing and presents a very convincing imitation of a specific type of female bee. The male bee of this specific species that is being impersonated hatch a few weeks prior to the female bees. What Ophrys sphegodes does is to time its bloom so that the flower coincides precisely with this period. Thus, when the male bees are actively looking for females to mate with, the Ophrys sphegodes 'offers' a possible target for these male bees. The poor male bees are thus bamboozled into wanting to copulate with the flower of the Ophrys sphegodes. These bees then pseudocoppulate with the orchid flower and pollination is affected.