A SUMMARY OF THE TAXA IN THE VASCULAR FLORA OF THE UNITED STATES, CANADA AND GREENLAND

A tabular summary, by family, of the 56,431 computerized names of those native and naturalized plant taxa included in the "Synonymized checklist of the vascular flora of the United States, Canada and Greenland" (including Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands) indicates a flora of 21,588 species in 2,921 genera in 254 families. There are also 740 named hybrids and, under current concepts, 2,491 subspecies and 8,008 varieties in our flora. There are 20,429 pertinent or "manual level" synonyms, with the number of synonyms exceeding the number of accepted names in many families (especially those families of high agricultural, horticultural or other economic importance). THE VASCULAR FLORA of North America represents the second most diversified group of higher organisms of the continental biota, being surpassed in numbers of species only by the enormous class Insecta. Yet, despite the desires and efforts of American taxonomists over the past century or more, there has previously been no biologically realistic enumeration of the many taxa of Tracheophyta in this vast and diverse area. However, through a cooperative effort between the Biota of Northi America Program and the North Carolina Botanical Garden, some 56,000 pertinent names from the extensive taxonomic data files of the senior author have been computerized, reviewed, evaluated, and appropriately synonymized by over 250 botanical specialists to produce a relatively complete and biologically valid checklist of our flora. The numerical comparison presented in Table 1 is a summary, by plant family, of the detailed data in the "Synonymized checklist of the vascular flora of the United States, Canada and Greenland" (including Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands) by Kartesz and Kartesz (1980). The 254 plant families listed in Table 1 essentially follow the concepts of Crabbe, Jermy and Mickel (1975) for the Pteridophyta, Little (1979) for the Gymnospermae, and the convenient conservative treatment of Windler and Windler (1973) for the Angiospermae. The treatment of the 2,921 genera, 21,588 species, 2,491 subspecies, 8,008 varieties, and 740 named hybrids generally represents the current status of these taxa in the eyes of the many I Received for publication 11 January 1980; revision accepted 4 February 1980. specialists who generously provided critical reviews of their particular groups. It should be noted that the two categories, subspecies and variety, are not mutually exclusive as tabulated here and that the synonymy concerned is generally given only to the functional or "manual" level. Therefore, the 20,429 synonyms (for all categories or ranks) likely represent a practical minimum number of synonyms for our flora, although the number might be reduced by 5 or 10% and still be functional. On the other hand, depending on the degree to which purely historic and monographic synonymy might be included, the list of synonyms in the checklist could easily be increased to 100,000 or more with little increase in general functional value. Clearly, we have long ago passed the point prophesied by de Candolle ". . . when botanists will have made, unmade, often remade, raised or lowered, and redefined several hundred thousand groups from classes to mere varieties, and when synonyms will have become much more numerous than accepted groups" (Weatherby, 1949). Until there was an appropriate and critical biological assessment and evaluation of such extensive synonymy by cooperating specialists, a realistic enumeration of the valid and accepted plant taxa of the area treated was impossible. With the Kartesz and Kartesz checklist we have the first accurate approximation of the total diversity of our flora, critically synonymized, which will provide a realistic and, hopefully, a somewhat standardized and stabilized reference base for many aspects of taxonomic, floristic and ecological work. Indeed, the checklist has already been of critical value toward the preparation of an "Atlas" and the planning for a "Guide" which could be further