The similarity in composition of families, genera, and species of vascular plants was analyzed from existing published data belonging to 12 localities of fir forests located on the transmexican volcanic belt. The similarity analyses were performed using classification and ordination multivariate statistical techniques. The vascular flora of these forests contains 76 families, 222 genera, and 510 species. From the analyses, It was possible to detect patterns in both com-position and structure of the forests which are important for their management and conservation: a small percentage of the most common families contains a very high proportion of genera and species; a small percentage of the most constant genera contains near 50% of the species; a scarce percentage of the species is common to the 12 fir forests localities which also define their fundamental structure. Most of the species distribution were not uniform among localities which stands out the importance of past and current local environmental conditions.