Of the several systems that have been proposed for classifying terrestrial plant life-forms, the most widely used in the phytogeographical literature ofthe twentieth century is that of Christen C. Raunkiaer. In addition to the three philosophical dicta linking plant form to ecological conditions, Raunkiaer adopted three practical guidelines for his classification system: (1) the basis for classifying life-forms must be structural and biologically important to survival and growth, (2) the features used must be readily observed under field conditions such that plants can be easily classified, and (3) the features must establish a homogenous system ofclassification that enables a statistical comparison of different vegetational types based on the frequency of life-forms in each vegetation type.
Raunkiaer selected a single criterion for classifying plants, that is, the location of perennating buds (shoot apical meristems) with respect to ground level. The logic of this system rests on the supposition that the location of buds is indicative of the degree of protection they are afforded from inclement climatic conditions. Using this single criterion, five major life-forms are recognized (Figure 2).
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