Phytosociology is a modem science which uses a methodology recognized by most plant ecologists to be the most efficient and effective way to explain natural vegetation patterns in a geographic area with a variety of ecological features. This approach is widely used in Europe, Asia, and North Africa, but not yet in North America. North American vegetation studies are very heterogeneous and the classification of plant communities has not been their objective. California is probably the region in the United States with most references on natural vegetation studies, but, unfortunately, the phytosociological approach has been used rarely on Californian vegetation. Major United States and Californian vegetation units are well-known, especially since KUCHLER'S works (1964, 1977). The synthesis on California published by BARBOUR & MAJOR (1977) and the general North American overview (BARBOUR& BILLINGS 1988) are also some basic references on modern North American vegetation bibliographies. These syntheses and classifications are not based on phytosociological methods, but on a combination of physiognomic, ecological, and floristic traits. Three years ago, Peinado and his colleagues started to publish descriptions and analysis of some plant communities using phytosociological methodology, especially in the Baja California region, as a result of J. Delgadillo's PhD. dissertation research in these areas (e.g. PEINADO et al. 1995). Recently, SAWYER & KEELER-WOLFF (1995) have also published descriptions of nearly 250 vegetation units they called "series". These units, in the author's view, are on a larger hierarchical scale than associations, and are not entirely based on a complete floristic composition. Moreover, the symphytosociological dynamic concept of vegetation series and associations is misapplied and the results are generally not satisfactory (REJMANEK 1997). A phytosociological synthesis for the classification of the major Californian vegetation units has recently been proposed by RIVAS-MARTfNEZ (1997), strictly following the Code of Phytosociological Nomenclature (BARKMAN et al. 1986). This impressive first approach describes, in an extensive monograph, all the recognized phytosociological units which have been precisely related to environmental and successional gradients. In this publication the effort to equate vegetation units described by Americans with phytosociological units is also