In the central area of the State of Chihuahua, 135 feld trips for collecting almost 6500 plant specimens were made in six years. A herbaria and bibliographic review and a study of the flora of the plains and low hills was also carried out. We recorded 112 families, 493 genera, 1322 species, and 232 infraspecific taxa of vascular plants. Of the total families, 87 were dicotyledons, 15 monocotyledons, 7 ferns and allies, and 3 conifers and allies. The families with highest number of genera and species were: Asteraceae (86, 235), Poaceae (50, 163), Leguminosae (45, 137), Brassicaceae (16, 25), Malvaceae (12, 29), Scrophulariaceae (11, 29), Cactaceae (10, 30), Verbenaceae (10, 24), Nyctaginaceae (7, 21) and Amaranthaceae (7, 18). The genera with highest number of species were: Muhlenbergia (37), Dalea (22), Euphorbia (21), Cheilanthes (19), Brickellia (17), Salvia (15), Cyperus (14), Quercus (13), Solanum (12), Eragrostis (12), Bouteloua (12), Erigeron (12), Astragalus (11), Ipomoea (11), Plantago (10), Acacia (10), Machaeranthera (9), Stevia (9), Opuntia (9), Aristida (9), Asclepias (9), Phaseolus (9), Oenothera (9), Viguiera (9) and Notholaena (9).The present study is a contribution to the knowledge of plant diversity in the arid lands of northern Mexico.
