An Orchidist's Miscellany

HYBRIDISATION 

 Orchids are unique amongst plants because of the ease with which they can be crossed, not only at the species level, but also between genera as well. This has been partly explained because orchids have a very large number of ovules and pollen tubes in each flower, In some cases the number of each running into millions. Even if two triploids are crossed, which usually is not considered feasible, there is a chance that a very small amount of viable seed will be produced.

Orchid species have evolved through each pollinator (mostly insects) becoming effective with a single species only. In most other forms of plant life, both species and generic separation is usually maintained by incompatibility mechanisms, both genetic and physical. In orchids, flower structure, colour, scent and flowering times, for example, have evolved in close association with a specific insect pollinator. This relationship is a prime factor which has lead to the extreme floral diversity apparent in the orchid family. Be- cause it is a breeding barrier which separates each species, if man comes along and engages In hand pollination, crosses between widely divergent species (and even genera as well) are able to produce viable seed.
Insects are the primary orchid pollinators, which constitute a variable and large group. The specific orchid/insect relationship can develop quickly into a stable one. Should, however, a new pollinator invade the area, or should the orchid become established in a new area where new and different pollinators are found, new species can rapidly develop. The process of cleistogamy .self fertilisation) is thought to have evolved in some species where it has invaded a new area devoid of suitable pollinators.

While there is an case of hybridisation, natural hybrids of epiphytes are rare, with the barrier of pollination specificity seldom naturally removed. In temperate areas, with many terrestrials, frequent hybridisation naturally can and does occur. The relationship of a species with its pollinator may not have developed to the same strength, especially in view of the fact that terrestrials are also more primitive in evolutionary terms.

In the development of the diversity apparent in orchids, and in the creation of the breeding barriers, the extreme diversity and specialisation of the habitats of each species, especially for epiphytes, is important. It is quite possible for a hybrid to be separated from either parent, or for a mutant to adopt a different micro-habitat even in the same general area, or in another through emigration. The specialisation of species and quick adaptability to diverse habitats has been a factor in the creation of so many orchid species for us all to grow and enjoy today.


Site established 9th May 1998