Many orchids produce pseudobulbs or false bulbs, although this is not always the case. Those that do, develop a svmpodial type of growth, where a new pseudobulb is added each season along a continually extending rhizome. In this way, the plant builds up a series of pseudobulbs that form a chain.
Cattleyas produce just one or two broad, semi-rigid leaves from the apex of the pseudobulbs. Leaves vary considerably in colour from a light mid-green to dark grey-green. Some paphiopedilums and phalaenopsis are mottled with light and dark green shades. Not all sympodial orchids produce pseudobulbs. The paphiopedilums and phragmipediums, for example, form fans of leaves from a basal rhizome. Monopodial orchids have a single vertical rhizome from which pairs of leaves grow at right angles. Vandas and phalaenopsis are the best examples of monopodial orchids in cultivation.
While the vandas can become considerably tall, and at some stage in their life need to be reduced in height, the phalaenopsis are selfregulating, never attaining much upward growth, because the older leaves are shed at the same rate as new ones appear. The leaves of vandas and other monopodial orchids are semi-rigid, while those of phalaenopsis are broad and flat. In the wild, the latter plants are not subjected to extreme temperatures or bright sunlight, and their wide surface is designed to catch as much of the filtered light as possible.
Some vandas, on the other hand, have rounded, or terete, foliage, which lessens the surface area on plants that can survive in areas of full sun. Leaves that remain for one or two seasons only are wide, soft and papery, such as with the lycastes, while leaves that are hard and leathery will live for much longer.
Pseudobulbs have evolved into an unlimited range of shapes and sizes, from long, thin, pencil shapes to rounded or even flattened structures. They may be no larger than a pea, round and shiny, and delicious to look at when newly formed, as in the smaller coelogynes and bulbophyllums. By contrast, they may be the size of a tennis ball, as in the case of some cymbidiums. In cattleyas and allied genera, they become tall and clubshaped, swelling out from a narrow base adjoining the stout rhizome, while the one or two leaves are formed at the top.
Some leafless monopodial orchids exist, such as Chilochista species, that are no more than a cluster of roots, and it is the roots that contain the chlorophyll to enable the plants to photosynthesize. A few orchids have thick hairs on both sides of the foliage.
The strangest of all are the hollow pseudobulbs of Schomburgkia tibicinis and Caularthon bicornutum, two species with slits at the base of their hollow pseudobulbs. It is difficult to be sure why these have evolved, because they defeat the object of functioning as a food store when they are completely empty. Usually occupied in the wild by a species of fierce ant, they can serve a dual purpose: providing a home for the insect, which, in turn, grooms the orchid and keeps it free from parasites and unwanted pests.
Some orchids, such as Trichotosia ferox, produce plants covered with fine, brown hair, the purpose of which is not fully understood. It is thought that the hairs may provide a layer of protection in cold climates. The stems, new shoots and base of the flower buds of Dendrobium infundibulum are covered with thick, black hairs, creating a rough surface. As the new growth starts to age, the hairs become less apparent.
