From the phytogeographical standpoint, ecology is frequently termed ecological plant geography.
In a general way, floristic plant geography is concerned with species, ecological plant geography with vegetation.
Ecological Classes.Many attempts have been made to divide plants and plant communities into classes depending on habitat factors.
The above classification by Warming, although it was without doubt the best ecological classification which had, at the time, been put forward, has not escaped criticism.
Md difficult to regard coniferous forests as a natural ecological group. At much higher altitudes, in the south-west of the Mediterranean region, forests occur of the Atlantic cedar (Cedrus atlantica).
The identity of plant form of many of the conifers of both temperate and of warm temperate districts is probably a matter of phylogenetic and not of ecological importance.
On the other hand, ecological plant geography seeks to ascertain the distribution of plant communities, such as associations and formations, and enquires into the nature of the factors of the habitat which are related to the distribution of plantsplant forms, species, and communities.
It is only in a general sense like Schimpers that such ecological terms as xerophytes have any value; and it is not possible, at least at present, to frame ecological classes, which shall have a high scientific value, on a basis of this nature.
One of the best known classifications on these lines is that by Warming.1 Warming recognized and defined four ecological classes as follows: Hydrophytes.These live in a watery or wet substratum, with at least 80% of water.
When the nature and effect of ecological factors have become more fully understood, it will be possible to dispense with the above artificial classification of factors, and to frame one depending on the action of the various factors; but such a classification is not possible in the present state of knowledge.