A very large monocotyledonous family, the orchid family, containing about 18 000 species in about 750 genera. Orchids are widely cultivated for their distinctive flowers, which may be recognized by the characteristic lower lip or * labellum. The anthers and carpels lie opposite the labellum and are fused into a structure called the column. The column is very diverse in form, the various modifications being related to the different pollinating animals. The pollen grains are clumped together into a definite number of pollen masses, termed * pollinia, on the column. Following pollination and fertilization, seeds are produced in vast numbers, but each contains only a rudimentary embryo. Seed maturation and germination is thus a lengthy process, which may take a number of years. In addition, orchids live in symbiotic association with various fungi and the appropriate fungus is needed before a seed can germinate. These factors have hindered the commercial multiplication of orchids though orchid growers have been quick to utilize tissue culture methods of multiplication. Orchid breeding is facilitated by the 'promiscuous' nature of orchids and the ease with which they form viable hybrids. This ability is demonstrated by the number of naturally occurring orchid hybrids, which exceeds those of all other plant families added together. About half the species of orchids (including most of the cultivated species) are epiphytic and thus need special compost mixtures. |
