Phytologia (November 1992) 73(5):353-377. VASCULAR FLORA OF BUENOS AIRES NATIONAL WILDLIFE REFUGE (INCLUDING ARIVACA CIENEGA), PIMA COUNTY, ARIZONA Steven P. McLaughlin Office of Arid Lands Studies, The University of Arizona, Tucson, Arizona 85721 U.S.A. ABSTRACT Buenos Aires National Wildlife Refuge in southeastern Arizona spans a relatively narrow elevation range and does not encompass much to-pographic diversity, yet possesses a diverse flora of 566 native species. A biseasonal rainfall regime and the presence of many aquatic habitats contribute to the high diversity. Floristic analysis shows that the Refuge belongs in the Apachian District of the Madrean Floristic Province. Most of the vegetation on the Refuge is grassland, much of it dominated by introduced species. There are, however, remnant areas of grassland with a dense cover of native, perennial grasses. These grasslands occur at a surprisingly low elevation for this vegetation type, probably be-cause of the relatively high rainfall in the Altar Valley. Also included in the Refuge is a unique low elevation cienega where many aquatic and mesophytic species occur at their lowest elevationad limits. KEY WORDS: Arivaca Cienega, Buenos Aires National Wildlife Refuge, Desert Grassland, Flora, Southeastern Arizona. INTRODUCTION The Buenos Aires National Wildlife Refuge was established in 1985 to preserve the habitat of the endangered masked bobwhite quail. Prior to 1985 all of the holdings were in active cattle ranches; there has been no cattle grazing since the Refuge was created. Within the Refuge there are desert grasslands composed of native, perennial species, that have been lightly grazed, and have not been extensively invaded by woody plants; there is also a low elevation cienega (marshland) along Arivaca Creek at Arivaca. The objective of this 353
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