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 353 354 PHYTOLOGIA volume 73(5):353-377 November 1992 paper is to catalogue the flora of Buenos Aires National Wildlife Refuge and briefly describe its vegetation. STUDY AREA The Refuge is located 90 km southwest of Tucson and covers 45,540 ha (Fig. 1). It lies mostly in the Altar Valley east of the Baboquivari Mountains; elevation ranges from 925 m, where the Altar Wash leaves the Refuge along its northern boundary, to 1400 m in the low lying Las Guijas Mountains along the eastern boundary. Most of the area within the Refuge occurs within an elevation range of only 200 m from 950 to 1150 m. In July 1989 a 660-ha parcel at Arivaca Cienega was purchased by the Nature Conservancy and transferred to the Refuge. Arivaca Cienega lies about 5 km upstream (east) of the Refuge on Arivaca Creek at an elevation of 1110 m. Climatic data for stations nearest the Refuge are shown in Table 1 (data from Sellers et al. 1985). Mean monthly temperatures reach maxima of 35° to 38° C in June and July and minima of 0° to 2° C in December and Jan- uary. Winter minimum temperatures are probably low enough to exclude many Sonoran Desert species. Creosote bush [Larrea tndentata [DC] Cov.), for example, has not been found within the Refuge. The distribution of rain- fall is biseasonal with a distinct summer peak in July and August and a less marked winter peak from December to February. The driest months are May and June; this time of year, known as the arid foresummer in southeastern Arizona, is the season most unfavorable to plant growth and survival. METHODS I initiated this study in March 1988. I spent a total of 35 days in the field between March 1988 and April 1991. During this time I made approximately 920 plant collections which have been deposited in the University of Arizona Herbarium (ARIZ). While in the field, I made notes on vegetation and on the distributions of the few taxa that were not collected (Cactaceae, Agavaceae, and some common trees and shrubs). Floristic affinities were investigated by assigning all species into floristic elements as defined in McLaughlin (1992) following the procedures in McLaughlin &: Bowers (1990). FLORA The total known flora of the Refuge consists of 93 families, 352 genera, 566 native species, 7 subspecific taxa, and 49 introduced species. The introduced McLaughlin: Flora of Buenos Aires National Wildlife Refuge 355 Fig. 1. Map of Buenos Aires National Wildlife Refuge, Pima County, Arizona. 356 PHYTOLOGIA volume 73(5):353-377 November 1992 TABLE 1. Climatic data from stations in the vicinity of Buenos Aires Na- tional Wildlife Refuge. Data are from Sellers et al. (1985); temperature in °C, precipitation in mm; temperature data are available only from the Anvil Ranch and Sasabe stations. species account for 8% of the total, which is somewhat high for a flora of this size. Aquatic and wetland species account for approximately 13% of the flora. The largest families in the flora are listed in Table 2. The composites (Asteraceae) and grasses (Poaceae) are by far the largest families with 96 and 88 species, respectively. The Poaceae also have the largest number of introduced species-18. Genera with five or more species in the flora are: Chamaesyce (spurges, 11 spp.), Bouteloua (grama grasses, 10 spp.), Cyperus (flat sedges, 9 spp.), Opuntia (choUas and prickly pears, 9 spp.), Muhlenber- gia (muhly grasses, 7 spp.), Aristida (three-awn grasses, 6 spp.), Boerhaavia (spiderlings, 6 spp.), BrtckelHa (6 spp.), Eragrostis (lovegrasses, 6 spp.), Erio- gonum (wild buckwheats, 6 spp.), /pomoea (morning glories, 6 spp.), Ascleptas McLaughlin: Flora of Buenos Aires National Wildlife Refuge 357 TABLE 2. Largest plant families in the flora of Buenos Aires National Wildlife Refuge. (milkweeds, 5 spp.), Astragalus (milkvetches, locoweeds, 5 spp.), Baccharis (5 spp.), Cryptantha (5 spp.), Lotus (vetches, 5 spp.), Oenothera (evening prim- roses, 5 spp.), Panicum (panic grasses, 5 spp.), Phacelia (5 spp.), and Poly- gonum (knotweeds, 5 spp.). The total number of native species (566) is rather high given the narrow elevational range (475 m), limited amount of field work, and relatively uniform vegetation. In a survey of local floras of Arizona, Bowers &: McLaughlin (1982) found that areas with a large amount of elevational relief, oak woodland and aquatic habitats, and a long collecting history had the richest floras. Their model would predict a flora of just 240 species for the Refuge based on its elevational range and collecting history (3 years-the Refuge area was rarely collected prior to 1988). Despite the low elevation range and lack of vegetational diversity, sev- eral ecological features at the Refuge contribute to its high species richness. One is the biseasonal distribution of rainfall. Winter rainfall and tempera- tures are high enough to support a significant winter annual flora of about 90 species. Many of these winter annuads are widespread in the Sonoran Desert, including several species of Asteraceae, Boraginaceae, Brassicaceae, Fabaceae, 358 PHYTOLOGIA volume 73(5):353-377 November 1992 Hydrophyllaceae, and Polemoniaceae. The majority of the herbaceous species, however, are phenologically active in the late summer and fall months following the summer rains. Riparian areas have many species that are absent from or uncommon in the surrounding grasslands. Major riparian areas on the Refuge include Ari- vaca Creek, Brown Wash, San Luis Wash, Altar Wash, Puertocito Wash, Lopez Wash, and Canoa Wash (Fig. 1). The most common riparian tree is Celtts reticulata Torrey (hackberry); Prosopts velutina Wooton (mesquite), Chilopsis linearis (Cav.) Sweet (desert willow), and Parkinsonia aculeata L. (Mexican paloverde) are also common, especially in the lower elevation areas. Other species of trees and shrubs found mostly along watercourses include: Aloysia gratissima (Gill. & Hooker) Troncosa, Brickellia califomica (Torrey & A. Gray) A. Gray, Brickellia floribunda A. Gray, Fraxtnus velutina Torrey, Juglans major (Torrey) Heller, Populus fremontii S. Watson, Quercus emoryi Torrey, Q. oblongifolia Torrey, Salix gooddingii Ball, Salix taxtfolia H.B.K., Sapmdus saponaria L. var. drummondii (Hooker &; Arn.) L. Benson, and Vitis arizonica Engelm. Many herbaceous species are more abundant in the shade of trees either in or along watercourses than in the adjacent grasslands, but few appear to be completely restricted to riparian sites. Lythrum californicum Torrey k. A. Gray and Oenothera rosea Ait. are found only at Arivaca Cienega and along Arivaca Creek; Helenium thurben A. Gray occurs only along Arivaca Creek. Several species in the flora are found only along Brown Wash in the north- western corner of the Refuge. Many of these are relatively mesophytic species that are more common at higher elevations in the Baboquivari Mountains to the west; because of the drainage of moisture and cold air down Brown Canyon these species are able to extend their ranges into the Refuge at lower eleva- tions. Species that have so far been found only in Brown Wash are: Agastache wrightii (Greenman) Wooton &c Standley, Cocculus diversifolius DC, Desmod- ium batocaulon A. Gray, Heterosperma pmnatum, Cav., Hybanthus attenuatus (Humb. &: Bonpl.) G.K. Schulze, Phacelia ramosissima Douglas, Sicyosperma gracile A. Gray, Sideroxylon lanuginosa Michx., Simmondsia chinensis (Link) Schneid., Sphaeralcea fendleri A. Gray, Thelypodiopsis linearifolia (A. Gray) Al-Shehbaz, and Tithonia thurberi A. Gray. The presence of aquatic habitats can greatly increase the plant diversity of an area (Bowers &: McLaughlin 1982). On the Refuge, stock tanks and reservoirs support species not found in the grasslands or riparian (wash) ar- eas. Relatively few strict aquatics (submerged, floating, and emergent plants) occur in the many impoundments found on the Refuge, possibly because these small bodies of water dry up frequently. Aquatics that have been found in tanks and reservoirs are: Heteranthera limosa (Swartz) Willd., Lemna minima H.B.K., Marsilea vestita Hooker & Grev., Polygonum pensylvanicum L., Pota- mogeton foliosus Raf., Potamogeton pusillus L., and Scirpus califomicus (C. McLaughlin: Flora of Buenos Aires National Wildlife Refuge 359 Mey.) Steud. Aquatic plants have excellent mechanisms for dispersal; it seems likely that additional species will be found in areas such as Aguirre I^ake and Mormon Lake if they are periodically monitored. Several species, which appear to depend on periodic desiccation of the lakes and tanks, are found almost exclusively along lake margins and dry bottoms, a habitat similar to the well known "vernal pools" of cismontane California. Species occurring exclusively or predominantly in this habitat in- clude: Alopecurus caroltnianus Walt., Astragalus nuttallianus DC. var. ce- droensis Jones, Eryngium heterophyllum Engelm., Hordeum pusillum Nutt., Lobelia fenestralis Cav., Myosurus minimus L., Oenothera flava (A. Nelson) Garrett, Potentilla rivalis Nutt., Verbena bracteata Lag. & Rodr., and Veronica peregnna L. ssp. xalapensis (H.B.K.) Pennell. The vegetation map of Brown & Lowe ( 1977) shows the entire area occupied by Buenos Aires National Wildlife Refuge as being desert grassland. This veg- etation type varies considerably in its physiognomy and species composition, however, depending on land use, soil depth, and slope aspect and angle. Most of the grasslands on the Refuge occur on relatively deep alluvial soils in the valley bottom. Although rocky, upland sites are not extensive on the Refuge, these sites do support a community with increased diversity of lifeforms and species. Species restricted to such upland grasslands include: Agave parvtflora Torrey, Anthericum torreyi Baker, Bouteloua eludens Griffiths, Cheilanthes spp., Coreocarpus arizonicus (A. Gray) Blake, Digitana msularts (L.) Mez, Dryopetalon runcmatum A. Gray, Ericameria laricifolia (A. Gray) Shinners, Erigeron neomexicanus A. Gray, Erythrina flabelhformis Kearney, Eysenhard- tia polystachya (Ortega) Sarg., Galactia wrightii A. Gray, Herissantia cnspa (L.) Briz., Heteropogon melanocarpus (Ell.) Bentham, Mammillarta heydert Muehl., Notholaena spp., Passtflora foetida L., Pellaea truncata Goodding, Phaseolus heterophyllus Willd., Schizachynum cirratum (Hack.) Wooton &: Standley, Tecoma stans (L.) H.B.K., and Trachypogon secundus (Presl) Scribn. Several species have so far been found in the Refuge only on the western and southern slopes of the Las Guijas Mountains. These include: Aloysia wnghtii (A. Gray) Heller, Cynanchum arizonicum (A. Gray) Shinners, Eu- patonum. soUdaginifolium A. Gray, Haplophyton crooksii L. Benson, Iresine heterophylla Standley, Plumbago scandens L., Quercus turbinella E. Greene, Senecio lemmom A. Gray, and Waltheria americana L. Since neither the Las Guijas nor the San Luis Mountains have been thoroughly explored, additions to the flora are likely to be found in these areas. A few mesophytic species that are usually found in Arizona at much higher elevations (often in pine forests) occur on the Refuge in grasslands but are very rare. Three such species co-occur just a few miles southeast of Refuge head- quarters: Eryngium, heterophyllum, Heterotheca ruttert (Rothrock) Shinners, and Aster falcatus Lindl. ssp. comm.utatus (Torrey Sz A. Gray) A.G. Jones-the latter is also found at Arivaca Cienega. Two other higher elevation grassland 360 PHYTOLOGIA volume 73(5):353-377 November 1992 species, Berlandiera lyrata Bentham and Cirstum ochrocentrum. A. Gray, are also restricted to a small area south of Refuge Headquarters. VEGETATION The dominant vegetation on the Refuge is grassland. There is no oak woodland, although three species of oaks do occur in the flora: Quercus em,oryi (Emory oak) and Q. oblongifolia (Mexican blue oak) are found only along a few watercourses in the southeast part of the Refuge, and Q. turbinella (scrub oak) is scattered in the Las Guijas Mountains. The grassland vegetation in the valley bottom varies in aspect and species composition across the Refuge. Areas mapped as grasslands just to the north of the Refuge on private and state owned lands are dominated by Prosopis ve- lutina, Isocoma tenutsecta E. Greene (burroweed), and Opuntia species; peren- nial grasses here essentially have been eliminated by overgrazing. Regrettably, much of the grassland in the Altar Valley and elsewhere in southeastern Ari- zona is in this poor condition. Within the Refuge, the grasslands on the north- ern, central, and western portions have a lush aspect but are dominated by a single species, the exotic perennial, Eragrostis lehmanniana Nees (Lehmann lovegrass). Prosopis velutina, Opuntia spp.. Acacia greggii A. Gray (catclaw acacia). Mimosa biuncifera Bentham (wait-a-bit), and other woody plants are often abundant. Another introduced species, Sorghum, halepense (L.) Pers. (Johnson grass), dominates the floodplains along the major washes. Along the eastern edge of the Refuge, up to the base of the Las Gui- jas and San Luis Mountains, where elevations are higher, slopes are steeper and rockier, and soils are more variable (including many calcareous sites), the grasslands are less disturbed and more diverse. The grassland southeast of Refuge Headquarters is dominated by several native perennials, including Aris- tida ternipes Cav., Bouteloua curtipendula (Michx.) Torrey, B. hirsuta Lag., B. repens (H.B.K.) Scribn. &; Merr., Bothriochloa barbmodis (Lag.) Herter, Digitarta califomica (Bentham) Henr., Eragrostis intermedia A.S. Hitchc, and Leptochloa dubia (H.B.K.) Nees. Also present are many native perennial herbs, Fouquieria splendens Engelm. (ocotillo), large and small cacti, and sev- eral Agavaceae [Agave palm.eri Engelm., Dasylirion wheeleri S. Watson (sotol), Nolina microcarpa S . Watson, and Yucca elata Engelm. (beargrass)]. On low ridge tops in this area the grass cover is dominated by Aristida purpurea Nutt. var. longiseta (Steud.) Vasey, Bouteloua chondrosioides (H.B.K.) Bentham ex S. Watson, B. eriopoda (ToTrey) Torrey, B. hirsuta, and Heteropogon contortus (L.) P. Beauv. ex Roemer &: Schultes; associated with these grasses are sev- eral low shrubs including Calliandra eriophylla Bentham, Krameria parvifolia Bentham, and Zinnia acerosa (DC.) A. Gray. McLaughlin: Flora of Buenos Aires National Wildlife Refuge 361 TABLE 3. Precipitation in major valleys in southeastern Arizona. Elevations (in meters) and precipitation (in mm j are from weather stations given in Sellers et al. (1985). These desert grassland communities are occurring at a very low elevation (1100 m) in Arizona for this vegetation type. Shreve (1951) states that true grasslands in Arizona are not found below 3500 feet (1067 m). The upper Altar Valley can support this native, perennial grassland at such a low elevation because it receives relatively high rainfall, comparable to that of other valleys in southeastern Arizona at higher elevations. In this part of the state there is a gradient of decreasing rainfall in going from west to east (Table 3). At 1200 m elevation the Altar and Santa Cruz Valleys receive about 400 mm of precipitation annually; rainfall at comparable elevations going eastward is about 300 mm in the San Pedro and Sulphur Springs Valleys and about 250 mm in the San Simon Valley. Most desert grasslands of the Southwest have been dramatically degraded by overgrazing and the introduction of exotic plant species. The extensive monospecific stands of Lehmann lovegrass that dominate the central portions of the Refuge probably developed no more than 20-30 years ago. This species was first introduced into southern .Arizona in 1932 by the Soil Conservation Service (Freeman 1979); this exotic grass now infests over 200,000 ha of for- merly native grassland (Cox &: Ruyle 1986). The spread of Lehmann lovegrass on the Refuge was probably facilitated 362 PHYTOLOGIA volume 73(5):353-377 November 1992 by grazing, since this exotic is less palatable than the native perennial grasses it has replaced (Cable 1971; Freeman 1979). The nearly monospecific stands of this species are not good habitat for the masked bobwhite, which requires more diverse grass-herb vegetation (Goodwin & Hungerford 1977) with legumes to provide seed and cover during the winter. Lehmann lovegrass stands have low diversity of native grasses, herbs, shrubs, grasshoppers, rodents, and birds, in comparison to stands of native perennial grasses (Bock et al. 1986). There are no records of what the grasslands looked like on the lower ele- vations at the Refuge prior to the introduction of Lehmann lovegrass. Haskell (1945) described a lightly grazed grassland at similar elevations (1130 m) on the Page Ranch on the northwest side of the Santa Catalina Mountains. This grassland was dominated by Anstida hamulosa Henr., A. purpurea var. longiseta^ Bouteloua rothrockii Vasey, B. curtipendula, B. eriopoda, and Hi- laria belangeri (Steud.) Nash. Brown (1982) suggests that the grasslands of the Altar Valley, prior to overgrazing and invasion of exotics, were similar to the Sonoran savanna grassland communities of the Plains of Sonora (one of Forrest Shreve's geographic subdivisions of the Sonoran Desert), which were dominated by Bouteloua rothrockii, several species of three-awn [Aristida cal- if ornica Thurber, A. hamulosa, A. termpes, A. wrightii Nash), other grama grasses [Bouteloua aristidoides [H.B.K.] Griseb., B. parryi [Fourn.] Griffiths, B. radicosa [Fourn.] Griffiths, B. repens), Chloris spp., and Heteropogon con- tortus. Today Rothrock grama [Bouteloua rothrockii), poverty three-awn [Aristida hamulosa), spidergrass (.4. termpes), Arizona cottontop [Digitaria cahfornica), and slender grama [Bouteloua repens) are most common along roadsides and in patches not dominated by Lehmann lovegrass. Spiderlings [Boerhaavia spp.), spurges [Chamaesyce spp.), purslanes [Portulaca spp.), globe amaranths ( Gomphrena spp.), and Gaura spp. are the commonest herbs. All these species were doubtless more abundant prior to the introduction of Lehmann lovegrass. Within the Lehmann lovegrass dominated areas there are occasional patches of curly mesquite grass [Hilaria belangeri); these patches have several charac- teristic herbs including Allium m,acropetalum, Rydb. and Luptnus hrevicaulis S. Watson. ARIVACA CIENEGA The term "cienegas" is used in the Southwest for midelevation wetlands with saturated, organic, reducing soils (Hendrickson & Minckley 1984). These wetlands were once much more abundant in the Southwest. They have been severely altered and diminished in areal extent by grazing, introduction of exotic plants, and downstream arroyo cutting. Arivaca Cienega is one of the better preserved cienega wetland communities in southeastern Arizona, and McLaughlin: Flora of Buenos Aires National Wildlife Refuge 363 it is also the most xeric, occurring further west and at a lower elevation than other remaining cienegas in the region. Hendrickson & Minckley (1984) suggested that a relatively impermeable dike of shales, sandstone, conglomerate, and limestone outcropping below Ari- vaca has forced groundwater up to the surface, creating permanent surface flow and marshlands. They stated that the current meadow area south of Ari- vaca (now incorporated into the Refuge) is a remnant of a once more extensive cienega system. The wetlands are now maintsuned by a concrete ford across Arivaca Creek which acts as a check dam to prevent upstream arroyo cutting. The vegetation at Arivaca Cienega can be divided into four communities or zones. Along the periphery there is a mesquite zone with Isocoma tenui3ecta (burroweed), Gutierrezia microcephala (DC.) A. Gray (snakeweed). Acacia greggii, Zizyphus obtusifolta (Hooker) A. Gray (gray thorn), and other spiny shrubs. This area was badly overgrazed prior to being added to the Refuge; most native perennial grasses and palatable forbs have been completely elim- inated. Inside the mesquite zone is a zone of Sporobolus wrightii Munro ex Scribn. (sacaton), best developed on the northern end of the cienega. This too has been heavily grazed but has withstood the stress of cattle much better than has the mesquite zone. Many forbs that are most abundant in the meadow zone extend sporadically into the sacaton zone. The meadow zone, the third community type, is a sward of grasses, sedges, and forbs that is wet in the spring and in the late summer following the summer rains. It differs from less heavily grazed southeastern Arizona cienegas in hav- ing a high cover of weedy forbs and grasses: Ambrosia confertiflora DC. and A. psilostachya DC. (ragweeds), Xanihium strumanv.Tn\j. (cocklebur), Poa annua L., and Polypogon monspeliensts (L.) Desf. (rabbitfoot grass). Nevertheless, numerous native cienega species not found elsewhere on the Refuge have per- sisted in the meadow zone; many of these are high elevation plants reaching their lower limits at Arivaca Cienega: Agropyron trachycaulum (Link) Malte, Ambrosia trtfida L., Bothriochloa saccharoides (Swartz.) Rydb., Carex chihua- hensis Mack., Cham,aesyce vermiculata (Raf.) House, Juncus balticus Willd., J. torreyiCow., Muhlenbergia asperifolia{Nees Sc Mey.) Parodi, Nothoscordum texanum Jones, Oenothera spectosa Nutt., Pyrrhopappus rothrockii A. Gray, Ranunculus macranthus Scheele, Setaria geniculata (Lam.) Beauv., Sidalcea neomexicana A. Gray, Sisyrinchium demissum, E. Greene, and Trifolium worm- skioldii Lehm. Many of the native perennials that are dominant in the meadow now (e.g., Bidens aurea [Ait.] Sherff and Ranunculus m,acranthus) probably increased as a result of grazing. Cover of grasses and sedges is likely to increase in the meadow zone as the area recovers from grazing. The innermost zone of the cienega consists of springs and permanently wet ground. Along many of the springs there are stands of Salix gooddmgii 364 PHYTOLOGIA volume 73(5):353-377 November 1992 (willow) with occasional Populus fremontii (cottonwood). These springs sup- port numerous species of wetland and aquatic plants not found elsewhere on the Refuge: Azolla mexicana Presl, Ber^la erecta (Huds.) Gov., Bidens lae- vis (L.) BSP., Ceratophyllum demersum L., Cyperus odoratus L., Eleochans bella (Piper) Svenson, Hydrocotyle ranunculotdes L. f., Leersta oryzotdes (L.) Swartz., Lemna gibba L., L. minor L., Myriophyllum exalbescens Fern., Pas- palum distichum L., Polygonum punctatum. Ell., Ranunculus hydrocharoides A. Gray, Sctrpus olneyt A. Gray, Typha latifolia L., and Zanmchellia palustris L. FLORISTIC AFFINITIES I have divided the western United States into three sets of floristic areas-5 floristic provinces for widespread species, 9 floristic subprovinces for species of intermediate range, and 20 floristic districts for narrowly distributed species (McLaughlin 1992). Widespread species were defined as those occurring in >20% of a set of 101 local floras covering the entire western U.S.A. west of the Great Plains; narrow species were defined as those occurring in <10% of these local floras. Associated with each floristic area is a floristic element-a group of species with more or less coincident ranges centered on the floristic area. Table 4 presents a summary of the floristic affinities of the flora of Buenos Aires National Wildlife Refuge, listing the numbers and percentages of species associated with the various floristic elements. The Refuge lies near the boundary of the Sonoran Floristic Province to the south, west, and north, and the Madrean Floristic Province to the east. Desert species are common, especially at the north end of the Refuge and among the winter annuals. Nevertheless, the species of Madrean and Apachian affinities clearly dominate in the flora, placing the Refuge in the Apachian District of the Madrean Province. Among widespread species, all 5 floristic elements are represented. The Madrean element is best represented (7.1% of the total flora), followed by the Sonoran (5.8%) and Californian (2.7%) elements. Among species with inter- mediate size ranges, the Madrean (20.1%), Sonoran (7.6%), and Californian (4.6%) elements are most important. The Apachian element (27.6%) accounts for more than half of the species with narrow ranges; Arizona Upland Desert (9.0%) and Chihuahuan Desert (5.3%) elements are also well represented. The techniques used here to classify species into floristic elements work best for species with more or less continuous ranges; i.e., most terrestrial species of upland, nonweedy habitats. Aquatic and wetland species often have wide, discontinuous ranges. Among the sample of 101 local floras from the western United States used to develop the floristic classification, aquatic habitats are well represented only in those floras from the California Floristic Province. Widespread and intermediate aquatic and wetland plants thus tend to be McLaughlin: Flora of Buenos Aires National Wildlife Refuge 365 TABLE 4. Floristic affinities of the flora of Buenos Aires National Wildlife Refuge. grouped into the Californian elements and narrowly distributed wetland plants tend to be placed in the Peninsular (southern) California element. THREATENED AND ENDANGERED SPECIES Thus far, few plants have been discovered in the Refuge that are on Fed- eral Threatened or Endangered Species lists or are candidates for these lists. Coryphantha 5c/ieeri (Kuntze) L. Benson var. robustisptna (Schoii) L. Benson (Pima pineapple cactus) is proposed endangered (Rutman 1992). Steve Do- brott, wildlife biologist at the Refuge, has found 21 individuals south of the Refuge headquarters on reddish adobe soil. Agave parviflora (small flowered agave) is a Category 2 species (Rutman 1992). It is widespread but rather un- common on the Refuge, occurring occasionally on rocky hilltops in the south- eastern portion of the Refuge north of the Las Guijas Mountains. Heterotheca rutten is a Category 2 species known on the Refuge from a single population in desert grassland south of the Headquarters. Amsoma grandiflora Alexander (Category 2), Coryphantha recurvata (Engelm.) Britton &: Rose (Category 1), 366 PHYTOLOGIA volume 73(5)'.353-3T7 November 1992 Cynanchum wigginsii Shinners (Category 2), and Phaseolus supinus Wiggins &: Rollins (Category 2) are known from sites adjacent to the Refuge. CHECKLIST The following checklist includes all vascular plants known to occur on Buenos Aires National Wildlife Refuge. Nomenclature in the following check- list follows Lehr (1978) and the supplements to that work (Lehr & Pinkava 1980, 1982), except for the Euphorbiaceae, which follows Kartesz & Kartesz (1980), and where otherwise noted. Taxa preceded by an asterisk (*) are introduced exotics. Pteridophyta ADIANTACEAE-C/iet/an. sophia (L.) Webb; Draba cuneifolia Nutt. var. mtegrifolia S. Watson; Dryopetalon runcmatum A. Gray; Erystm.um capitatum, (Douglas) E. Greene; Lep- idtum. lasiocarpum Nutt. var. lasiocarpum; L. thurberi Wooton; L. vir- ginicum L. var. m,ediuw. (E. Greene) C.L. Hitchc; Lesquerella gordoni (A. Gray) S. Watson; * Nasturtium, officinale R. Br.; * Sisymbrium, irio L.; Thelypodiopsis linearifolia [A. Gray) Al-Shehbaz; Thysanocarpus curvipes Hooker var. elegans (Fischer & Mey.) Robins. CACTACEAE-Carne^iea gigantea (Engelm.) Britton &; Rose; Coryphan- tha scheeri (Kuntze) L. Benson var. robustispina (Schott) L. Benson; C. vivipara (Nutt.) Britton &: Rose var. bisbeeana (Orcutt) L. Ben- son; Echinocereus fasciculatus (Engelm.) L. Benson var. fasciculatus', E. fendleri (Engelm.) Rumpler; E. pectmatus (Scheidw.) Engelm. var. McLaughlin: Flora, of Buenos Aires National Wildlife Refuge 369 ngidisstmus (Engelm.) Engelm.; Ferocactus wislizenii (Engelm.) Britton & Rose; Mammillaria heyden Muehl. var. heyden [M. gummifera En- gelm. var. applanata (Engelm.) L. Benson]; M. macdougalii Rose [M. gummifera Engelm. var. m.acdougalii (Rose) L. Benson]; M. microcarpa Engelm.; Opuntia arbuscula Engelm.; 0. engelm.annit Salm-Dyck [0. phaeacantha Engelm. var. discata (Griffiths) L. Benson & Wadkington]; 0. fulgida Engelm. var. mamm.illata (Schott) Coulter; 0. leptocaulis DC; 0. m,acrorhiza Engelm. var. m,acrorhiza\ 0. phaeacantha Engelm. var. majOT Engelm.; 0. spmosior (Engelm. & Bigelow) Toumey; O. versi- color Engelm.; 0. violacea Engelm. var. santa-rita (Griffiths & Hare) L. Benson. CAMPANULACEAE-Lo6e/za/ene5llr^emone pleiacantha E. Greene ssp. pleiacantha; Cory- dalis aurea Willd.; Eschscholtzia califormca Cham. ssp. mexicana (E. Greene) C. Clark. PASSIFLORACEAE-Pa55ty?ora /oefirfa L.; P. mexicana Juss. PHYTOLACCACEAE- /2zwna humUis L. PLANTAGINACEAE-*P/ania^o majorh.; P. patagomca 3 acq. var. gnaphalo- ides (Nutt.) A. Gray; P. virginica L. PLUMBAGINACEAE-P/um6a^o scandens L. POLEMONIACEAE-.4//op/iy//um gilwides (Bentham) A. & V. Grant; Eri- astrum diffusum (A. Gray) Mason; Gilia mexicana A. &: V. Grant; G. ophthalm,oides Brand, ssp. australis A. &: V. Grant; Ipomopsis longiflora (Torrey) V. Grant; Lmanthus aureus (Nutt.) E. Greene; Microsteris gra- cilis (Hooker) E. Greene. POLYGALACEAE-Po/yja/a barbeyana Chodat. POLYGONACEAE-fi'rioyonum abertianum Torrey; E. deflexum Torrey var. turbmatum (Small) Reveal; E. polycladon Bentham; E. thurbert Torrey; E. trichopes Torrey; E. wrightii Torrey; * Polygonum, aviculare L.; *P. lapathifolium L.; P. pensylvanicum L.; *P. persicaria L.; P. punctatum Ell.; * Rumex crispus L.; R. hymenosepalus Torrey. PORTULACACEAE-Ca/anlyenia compacta L.; Waltheria amencana L. TAMARICACEAE-*Tamarti ramosissima Ledeb. ULMACEAE- Ce/hs pallida Torrey; C. reticulata Torrey. URTICACEAE-Farzeiarta hespera Hinton. 374 PHYTOLOGIA volume 73(5):353-377 November 1992 VERBENACEAE- /l/oysia gratis sima{G\\\. k Hooker) Troncosa; A. wnghtii (A. Gray) Heller; Glandularia bipinnatifida (Nutt.) Nutt. var. btpinnat- ifida; * Phyla cunetfolia (Torrey) E. Greene; Tetraclea coulten A. Gray; Verbena bracteata Lag. k Rodr.; V. gracilis Desf.; V. neomexicana (A. Gray) Small. VIOLACEAE-//yiani/ius attenuatus (Humb. & Bonpl.) G.K. Schulze; H. ver- ticillatus (Ort.) Baill. Vise ACE AE-Phoradendron californicum Nutt.; P. tomentosum (DC.) A. Gray ssp. tomentosum. VITACEAE- V'i