Vessels inRoots stems

Roots only roots + stems + leaves

Figure 4 Distribution of vessels with simple or scalariform perforation plates (see insert diagrams) in the roots, stems, and leaves of extant representatives of the families of monocotyledons and the habitat preferences of families. Arrows denoted the directions of presumed evolutionary transitions. The ancestral life-form is assumed to be an aquatic herb with vessels (possessing scalariform perforation plates) restricted to roots (e.g., representatives of the Potamogetonaceae). Evolutionarily highly derived groups include tropical arborescent life-forms with vessels (possessing both scalariform and simple perforation plates in roots, stems, and leaves (e.g., Eriocaulaceae and Xyridaceae)), and arborescent or herbaceous stem and leaf succulent life-forms with vessels (possessing only simple perforation plates) in roots only (e.g., Liliaceae). Adapted from Carlquist S (1975) Ecological Strategies ofXylem Evolution. Berkeley, CA: University of California Press.

Figure 4 Distribution of vessels with simple or scalariform perforation plates (see insert diagrams) in the roots, stems, and leaves of extant representatives of the families of monocotyledons and the habitat preferences of families. Arrows denoted the directions of presumed evolutionary transitions. The ancestral life-form is assumed to be an aquatic herb with vessels (possessing scalariform perforation plates) restricted to roots (e.g., representatives of the Potamogetonaceae). Evolutionarily highly derived groups include tropical arborescent life-forms with vessels (possessing both scalariform and simple perforation plates in roots, stems, and leaves (e.g., Eriocaulaceae and Xyridaceae)), and arborescent or herbaceous stem and leaf succulent life-forms with vessels (possessing only simple perforation plates) in roots only (e.g., Liliaceae). Adapted from Carlquist S (1975) Ecological Strategies ofXylem Evolution. Berkeley, CA: University of California Press.

assumption that these criteria permit inferences regarding physiognomic-climatic correlations. Extensive adaptive convergent evolution has occurred during plant evolution. Therefore, plant life-form classification systems rarely, if ever, sort species into natural taxonomic categories. No generally accepted life-form classification system exists for the algae. However, developmental criteria allow algal species to be sorted into three basic life-forms that permit inferences about modes of existence and broad habitat preferences (i.e., unicellular, colonial, and multicellular). The most frequently used life-form classification system for land plants is that of Christen Raunkiaer. This system is based on a single criterion (i.e., the extent to which renewal buds are protected against inclement weather conditions). Five major plant life-forms are recognized on the basis of this criterion (i.e., phanerophytes, chamaephytes, crypto-phytes, hemicryptophytes, and therophytes). Limited insights into the evolution of life-forms can be inferred using this system. Deeper insights are often gained by determining the phyletic distribution of anatomical features, particularly those of water-conducting elements, among closely related extant plant families.

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