Lilium is an old genus which apparently developed in the temperate and subtropical zones of the Northern Hemisphere. It is, indeed, confined to these zones – no lilies are known south of the Equator.
Many species were lost during the evolution of the genus: some species were unable to adapt themselves to changing geological and climatic circumstances; others only colonized comparatively small regions, and were overtaken by unsuitable conditions before they could spread into surroundings more congenial to their preservation. Precise details are lacking, and the available knowledge of wild varieties is rudimentary and full of gaps. The origin of some isolated lilies reaches very far back, while otherdeveloped much later and are therefore still closely related today.
The first classification of lilies was made in 1836 by the Austrian botanist, Stcphan L. Endlicher, and was revised in 1925 by E. H. Wilson in his book The Lilies of Eastern Asia. This classification was unfortunately both unsatisfactory and unnatural, because it was based only on the shape and bearing of the flower, and consequently split several closely related lily groups, particularly groups of American origin.
A recent classification, put forward by H. F. Comber in the Royal Horticultural Society Lily Year book for 1949, does not confine itself to the flower shape only, but includes a host of other characteristics, notably germination of the, arrangement of , and shape of bulbs and scales. It led to a new, more logical classification of the species, one which on the whole corresponded more closely to their evolution.
In the Royal Horticultural Society Lily Year book for 1968, Dr R. W. Lighty produced a diagram of the evolution of the genus Liliuni which takes into consideration all the different characteristics and also the migration of lilies. It gives a complete picture of the genus and the interrelationships between its species.