South-central Mexico Research Articles

Structural Evolution of the Guadalupe Mountains, South-Central New Mexico and West Texas: ABSTRACT

The Guadalupe Mountains of south-central New Mexico and west Texas occupy a unique physiographic and structural position. Physiographically, the mountains lie on the boundary between the block-faulted Basin and Range province to the west and the stable Great Plains province to the east. Structurally, the mountains form the northwestern margin of the Delaware basin, a prolific petroleum-producing region. A combination of field observation, subsurface correlation, and map and photo interpretation has revealed four important phases in the complex structural evolution of the Guadalupe Mountains and adjacent Delaware basin. Pennsylvanian to Early Permian (Wolfcampian) faulting and folding created the Huapache monocline and initially defined the limits of the Delaware basin. Permian flexing and differential subsidence accentuated the shelf-to-basin transition and resulted in deposition of the prograding carbonate shelf sediments now exposed in the Guadalupe Mountains. Late Cretaceous to early Tertiary (Laramide) deformation created the Carlsbad and Guadalupe Ridge folds, a series of anticlines and synclines in the eastern mountains. Late Tertiary (post-Ogallala) to Pleistocene uplift and tilting brought the mountains to essentially their present configuration. The western border of the uplift is defined by Basin and Range-type normal faulting, whereas the eastern margin is both faulted and monoclinally folded. Minor faulting has been active into Holocene time. End_of_Article - Last_Page 511------------

Seasonal adaptations of populations of the southwestern corn borer, Diatraea grandiosella, from tropical and temperate regions

Seasonal adaptations of populations of the southwestern corn borer, Diatraea grandiosella, obtained from south-central Mexico (19°N latitude) and southeast Missouri (37°N latitude) were compared. Day length and temperature were found to serve as environmental cues to programme the larval diapause of both populations, but different critical values were observed. The critical day length for diapause induction was about 13 hr light/day for Mexican larvae and about 15 hr light/day for Missouri larvae, and was relatively stable at 20 to 30°C. Mexican larvae displayed a less-intense diapause than did Missouri larvae. Some diapausing Mexican larvae maintained at 25 or 30°C pupated in about 15 days, regardless of the day length to which they were exposed. The rate of diapause development of Mexican larvae was high at day lengths between 14 hr and 16 hr, whereas that of Missouri larvae was accelerated at day lengths of 16 hr at 25 and 30°C. Diapause development of Mexican larvae was virtually unaffected by chilling at 10°C, whereas that of Missouri larvae continued at a low rate at 10°C. Selection of Mexican larvae for diapause showed that only four generations were needed to significantly increase the incidence of diapause.

A New Lecanoric Acid-Producing Usnea from Mexico

Usnea lecanorica (Ascomycotina, Usneaceae), a new species of the U. florida group from south-central Mexico, differs from all other known species of its genus by producing lecanoric acid as the major medullary constituent. The new Mexican lichen species Usnea lecanorica (Ascomycotina, Usneaceae), the subject of this report, is the first member of its genus known to produce lecanoric acid. Unlike the some 18 0-orcinol products characteristic of many scores of species in this genus, lecanoric acid is a para-depside of the orcinol series, a category previously known to be represented in Usnea by only evernic acid in U. longissima ssp. jesoensis Asah. and U. trichodea Ach. Evernic acid is the 4-O-methyl derivative of lecanoric acid; it probably also occurs in trace amounts in the new species described here. The natural but variable genus Usnea (discussion: Krog 1976) consists of about 500 species. Although thoroughly cosmopolitan, it achieves greatest species diversity in warmtemperate, subtropical and upland-tropical vegetations. The fruticose thallus with its central cord is so distinctive that the chemical data now recorded from approximately 200 species are surely correctly assigned at the generic level. Taxonomy at the species level, however, is confused because in many groups the major evolutionary modifications have been in secondary-product chemistry and amplitude of ecologic tolerance. Usnea lecanorica belongs to the U. florida complex--characteristically tufted lichens with conspicuous apotheciaconstituting in North America a series of 13 chemotypes as determined from a thin-layer chromatographic survey of 358 specimens (Fiscus 1972). No micromorphological analyses have been made, and consequently it is unknown if any of the small morphological variations seen in the U. florida complex consistently accompany major chemical discontinuities. The U. florida group in North America is characterized by certain 0-orcinol depsides (diffractaic, squamatic and thamnolic acids) and depsidones (connorstictic, constictic, 2'O-methylpsoromic (= conpsoromic), fumarprotocetraric, galbinic, norstictic, protocetraric, psoromic, salazinic and stictic acids). Additionally, some members of the U. florida group make fatty acids (including caperatic and bourgeanic acids); they all make the yellow pigment usnic acid and some produce other pigments as well. It was consequently a surprise to find two C+ red Mexican collections that produced the unsuspected orcinol depside lecanoric acid. The two small original collections were made by Robert W. Cruden in 1966 at a mountain locality some 25 km southwest of Toluca in the state of Mexico. We found four more specimens at the same locality ten years later during one of several general collecting trips for lichens of the mountain forests of south-central Mexico. Curiously, these four were the only examples of this chemotype among the many specimens of the U. florida group taken throughout the extensive regions visited. The cool, relatively moist locality near Toluca is above 3000 m elevation and is forested with Abies religiosa and Pinus sp. The new species grows upon both these trees. The most common congeneric companion 007-2745/83/254-256$0.45/0 This content downloaded from 207.46.13.163 on Fri, 08 Jul 2016 06:11:51 UTC All use subject to http://about.jstor.org/terms 1983] CULBERSON ET AL.: A NEW USNEA 255

Structural Analysis of Three Rivers Redware Designs

ABSTRACTStructural analysis of complete and fragmentary designs on prehistoric Three Rivers Red-on-terra-cotta and Lincoln Black-on-red bowls from south central New Mexico defines more specifically the long recognized continuity in decorative tradition between them. The resulting classification of design lays the groundwork for future research on archaeological problems to which they are pertinent, including the nature of exchange interaction within the region and relationships to other regions.

Vegetational Evaluation of Pinyon-Juniper Cabling in South-Central New Mexico

Vegetational Evaluation of Pinyon-Juniper Cabling in South-Central New Mexico

Waterponding for Increasing Soil Water on Arid Rangelands

Waterponding for Increasing Soil Water on Arid Rangelands

Color Pattern Variation in Crotalus lepidus lepidus (Viperidae) in Southwestern Texas

Geographic isolation and adaptation have combined to produce two different popula- tions of Crotalus 1. lepidus in southwestern Texas. Statistically significant differences in background color-matching are the result of adaptation to dominant substrate colors that differ sharply between ranges of the two populations. Uniformly dark primary blotches in combination with pink and buff ground colors characterize the Davis Mountains-Big Bend population which is confined mainly to the darkly weathered volcanic rocks of the Davis Mountains and Big Bend region. The Stockton-Edwards Plateau population occurs on the more lightly weathered limestones of the Stockton and western Edwards plateaus, and displays ground colors of various shades of gray combined with a pronounced anterior fading of the primary blotches. Snakes of the Davis Mountains-Big Bend population have a significantly higher mean number of primary blotches than those of the Stockton-Edwards Plateau population. Stretches of desert flatland serve as effective barriers, limiting gene flow and enabling populations to respond separately to selection pressure applied by need for concealment from predators and/or prey. Background color-matching is a frequently observed adaptation of animals to their environment. However, among the many species of snakes that display this trait, documentation of adaptation involving color or color pattern is rare. Dunn (1942) noted the paucity of work on natural selection in snake populations and remarked on the value of these reptiles for such studies. Camin and Ehrlich (1958) and Ehrlich and Camin (1960) effectively demonstrated color pattern selection in Lake Erie island populations of Natrix sipedon. They observed statistically significant differences between pattern types of young and adult members of a population. From young adult to adult, those with banded patterns were being eliminated in favor of the unbanded. They interpreted this to be a response to selection pressure applied by avian predators such as gulls, herons, and raptors because, to the human eye, banded snakes were highly conspicuous, whereas the unbanded were well camouflaged. Similar results were obtained by Beatson (1976) from a population of N. s. sipedon in Kansas. These conclusions are in agreement with the widely held view that most background-color matching in animals has developed as a result of natural selection by predators that rely on vision for prey detection (Portmann, 1959). Among rattlesnakes, few species or subspecies exhibit background color- matching better than the Mottled Rock Rattlesnake, Crotalus lepidus lepidus (Kennicott), of southwestern Texas, south-central New Mexico, and the Sierra Madre Oriental in Mexico. The basic color pattern consists of a series of well defined primary dorsal blotches, which become transverse bands posteriorly. Primary blotches alternate with a series of one to three less distinct secondary blotches. The primaries and secondaries vary in contrast but produce the effect of a mottled, banded snake (Fig. 1). This pattern in combination with various ground colors blends in exceptionally well with the substrate upon which the snake is found. The degree of stippling on individual scales also contributes significantly to the overall camouflage effect. THE SOUTHWESTERN NATURALIST 27(3):263-272

Seasonal Movements of Mexican Freetail Bats Tadarida brasiliensis mexicana Banded in the Great Plains

Records of band recoveries from 170,000 bats banded in northern Oklahoma between 1952 and 1968 are summarized to present an account of the migratory habits of the Great Plains population of this species. Winter range lies between 20° and 29°N, and between the Gulf of Mexico and the interior of the Mexican Plateau. Maximum recorded distance from banding site to point of recovery is 1,840 km. One bat was recovered in its natal cave after making eight migra- tory circuits. A theory regarding the use of olfaction in long-range navigation is presented. The Mexican freetail bat has been known since 1956 to be a migratory species (Villa, 1956; Glass, 1958, 1959; Villa and Cockrum, 1963). Since the first discovery of long-range migration, Constantine (1967) has summarized his data on activity patterns and recorded numerous records of movements to and from Carlsbad Cavern. Cockrum (1969) summarized data he obtained in northwestern Mexico and southern Arizona. He recognzied four discrete populations, those in California and western Arizona which perform only local or short-range movements, and those of the intermontane desert and the Great Plains, which perform long migratory flights. The Arizona-New Mexico population migrates south along the Sierra Madre Occidental and the west coast of Mexico at least as far as the state of Sinaloa; the Great Plains population moves southward through Texas and along the Sierra Madre Oriental into eastern and south-central Mexico. Cockrum recorded two instances of movement of banded bats from Carlsbad to Arizona and northern Sonora, and Constantine recorded three recoveries of his Carlsbad bands in Arizona and one in Sinaloa. These records constitute the only evi- dence of intermixing between the Great Plains and Interior Desert populations. Between 1952 and 1968 the author and his graduate students banded approximately 170,000 of these bats in western Oklahoma. In the early years bats were banded without regard to age, but from 1962 to 1968, about 120,000 neonates were banded, males and females in about equal numbers. The bats came from four caves less than 80 km apart, whose populations constantly intermingle. These four caves constitute the northernmost nursery aggregation of freetail bats in the Great Plains and collectively con- tain an estimated >3 million fledged bats in late summer when all neonates are fully capable of flight. By using a different-colored band each year, with colors being repeated only at 5-year intervals, it was possible to recognize our bats, as opposed to bats banded elsewhere, and to recognize year classes, without capturing bats to read the numbers. From 329 bands actually read, and many hundreds more seen and recognized as ours, it appears that a large part of the population returns each year to its natal area. However, numerous summer records (Fig. 9) indicate that many bats of both sexes

Direct evidence of a subducted plate under southern Mexico

The hypothesis1 of subduction of oceanic plates under active continental margins has become a fundamental idea in plate tectonics. Yet the evidence for the existence of oceanic plates beneath continental borders is still largely circumstantial. In seismology, the presence of a new layer or structural unit is taken as confirmed only after seismic phases corresponding to reflections or refractions from that layer have been identified on seismograms. I report here the presence of a mantle phase, interpreted as a seismic wave refracted from a dipping interface on records of aftershocks from the intermediate earthquake of 24 October 1980 in the Mixtec Highlands of south-central Mexico which may be direct evidence on the structural position of the subducted plate under the Mexican active continental margin.

Response of Chihuahuan Desert Mountain Shrub Vegetation to Burning

The effects of fire on vegetation in the desert mountain shrub community were studied on 3 to 7-year-old burned sites near the northern limits of the Chihuahurn Desert. Coverage and frequency of redberry juniper (Juniipcruspinchotii) and frequency of whitebail acacia (Acacia texends) were lower, while frequencies of catclaw mimosa (Mimosa biunc~em) and skeleton goldeneye (Viguiera stenoloba) were higher on burned sites when_compared with unburned paired piants. Lechuguiiia (Agave lecheguil&, sotoi (DasytYrion leiophylbun), and sacahuista (Nor and Texas Tech University. It is a contribution of College of Agricultural Sciences, Publication No. T-9-235. Texas Tech University. Manuscript received March 28, 1980. huan Desert. Bunting and Wright (1977) reported theeffectsof fire on desert mountain shrub vegetation 2 years after burning in the Texas Big Bend country. Kittams (1973) noted that in burned desert mountain shrub communities, catclaw mimosa (Mimosa biuncifera). skunkbush (Rhus aromatica), silver dalea (Dalea argyraea), skeleton goldeneye (Viguiera stenoloba). mountain mahogany (Cercocarpus montanus), scrub oaks (Quercus spp.), redberry juniper (Juniperus pinchotii) and alligator juniper (J. deppeana) usually recovered through some form of vegetative sprouting. He observed that lechuguilla (Agave lecheguilla), datil (Yucca baccata), and mature soto (Dasylirion leiophyllum) were usually killed by fire. ,Bunting and Wright (1977) found that fire reduced shrub cover and total grass cover 43% and 72% respectively in a desert mountain shrub community 2 years after burning. Coverage of forbs and half shrubs increased 650%. The fire significantly reduced the density or cover of sideoats grama (Bouteloua curtipendula), blue three-awn (Aristida glauca), sotol, and lechuguilla, whereas coverage contributed by skeleton goldeneye tripled through vigorous sprouting and seedling establishment on the burned area (Bunting and Wright 1977). Information pertaining to other species common to the Chihuahuan Desert is available from studies conducted elsewhere. Mortality rates for cholla (Opuntia imbricata) and pricklypear (0. phaeacantha) two growing seasons after a prescribed burn on the Texas High Plains averaged 45% and 68%, respectively (Heirman and Wright 1973). Pricklypear mortality was 3270 the first year following a prescribed burn (Cable 1967) and 28% the second growing season after an experimental tire (Reynolds and Bohning 1956), in two separate studies conducted in the Arizona Sonoran Desert. Survival of ocotillo (Fouquieria splendens) following a 62 JOURNAL OF RANGE MANAGEMENT 35(l). January 1999 wildfire in the Sonoran Desert was 33Ycfor heavily damaged plants and 50% for plants only scorched (White 1969). Regeneration occurred primarily through basal sprouting. Algerita (Berberis trifoliolata) sprouted vigorously following a wildfire in south central New Mexico (Dwyer and Pieper 1967). The objective of this study was to document longer term effects of fire on vegetation in the mountain shrub community of the Chihuahuan Desert by examining 3 to ‘I-year-old burned areas.

Behavior of the Temperature Structure Parameter in a Desert Basin

Measurements of the optical refractive index structure coefficient Cn2 and the temperature structure coefficient CT2 were made over the Tularosa Basin of south central New Mexico using both tower and aircraft mounted instruments. The height dependence of CT2 agrees reasonably well with the predictions of similarity theory in the daytime. However, the nighttime profiles disagree significantly from the surface-layer predictions for z/L > 0.05. Two factors can explain this disagreement: 1) for strong stabilities, the boundary layer is not fully turbulent, and 2) in the absence of strong synoptic forcing, mountain drainage flows may modify the profiles. The magnitude of CT2 during the daytime is found to be closely correlated with the difference in temperature between the surface and the air; in addition, there is a small dependence on wind speed. Measurements of CT2 through the depth of the convective mixing layer during the day agree closely with the model of Kaimal et al. (1976). These results imply that a single measurement or estimate of CT2 in the surface layer can be used to estimate the average profile of CT2 up to the inversion height during the day.

The Eocene biostratigraphy of New Mexico

The San Jose, Galisteo, and Baca Formations are continental deposits in New Mexico containing Eocene vertebrate fossils. The Almagre and Largo local faunas of the San Jose Formation in the San Juan basin are Lysitean (middle Wasatchian). The Cerrillos local fauna of the Galisteo Formation also is Wasatchian, possibly Lysitean. Strata of the Baca Formation in south-central New Mexico contain the titanotheres Palaeosyops sp. and cf. Manteoceras sp. and are the only Bridgerian strata known in New Mexico. The Tonque local fauna of the Galisteo Formation and fossil vertebrates from the Baca Formation in west-central New Mexico are correlatives of the Lapoint (Utah), Pearson Ranch (California), and Porvenir (Texas) local faunas and are Duchesnean. Precise placement of the Paleocene-Eocene and Eocene-Oligocene boundaries in New Mexico using vertebrate biostratigraphy is impossible because of a lack of fossils at critical horizons. The near absence of Bridgerian and total absence of Uintan fossils in New Mexico may result from a lack of collecting, particularly in parts of the Baca Formation.

The silica heat flow interpretation technique: Assumptions and applications

We have previously established a linear relation between temperatures based on the silica content of groundwater and regional heat flow and used the relation to prepare a new heat flow map of the continental United States. We now examine the assumptions upon which the relation is based, the accuracy to which groundwater silica data can be used to estimate regional heat flow, and the limitation of the technique. By averaging silica geotemperatures and traditional heat flow values over 1°×1° blocks, the linear regression is TSiO2 = mq + b, where m and b are constants determined to be 680±67°C m2 W−1and 12. ±5.1°C. The physical significance of b is mean annual surface temperature, and the product of m times thermal conductivity reflects the minimum mean depth to which groundwaters may circulate. These values are not sufficiently different from our earlier values (m = 670, b = 13.2) to justify using the newer values. To illustrate the application of the linear regression in predicting regional heat flow, data sets are presented from upstate New York, south central New Mexico, and Egypt. In each case, the predicted heat flow is tectonically reasonable and consistent with whatever traditional data are available.

A New Subspecies of Eutamias quadrivittatus (Rodentia: sciuridae) from the Organ Mountains, New Mexico

Patterns of bacular morphology in the Eutamias quadrivittatus species complex were analyzed to determine the identity of the Eutamias population inhabiting the Organ Mountains of southcentral New Mexico. The bacula of 124 animals from all geographically adjacent taxa in this complex ( E. q. quadrivittatus , E. einereicollis cinereus , E. c. cinereicollis , E. canipes sacramentoensis , E. c. canipes , and E. bulled durangae ) were examined. Bacular data demonstrate the close phyletic relation of the Organ Mountain population with E. q. quadrivittatus , rather than with E. cinereicollis cinereus to which it is currently assigned. This conclusion is supported by karyotypic evidence. However, aspects of morphology and ecology indicate that the Organ Mountain population represents a new subspecies. The divergence of this form from E. q. quadrivittatus probably occurred in Recent time as a consequence of isolation, small population size, and a unique environment.

Stuessya (Asteraceae: Heliantheae), a New Genus from Southcentral Mexico

Stuessya, a new genus from the Pacific slopes of southcentral Mexico is described. It is comprised of three species:S. apiculata, previously assigned to the genusViguiera;S. perennans, the generotype; andS. michoacana. The latter two taxa are previously undescribed. The genus is characterized by its urceolate, sclerified (at maturity) involucre. Chromosome counts of2n = 34 are reported forS. perennans. Relationships are problematical, but are reckoned to be somewhere betweenAldama andViguiera.

The Mississippian System of New Mexico and Southern Arizona: ABSTRACT

Lower Mississippian rocks of New Mexico and southern Arizona (pre-zone 7 Tournaisian age) are unconformable on rocks of Late Devonian to Precambrian age. Mississippian rocks were deposited during transgression on a surface of low relief. Tournaisian transgression began in southern Arizona, depositing the Escabrosa Limestone and, in southwestern New Mexico, the Keating (207 m), Caballero (18 m), and Lake Valley (180 m) Formations. At the end of Tournaisian time, epicontinental seas flooded southern and central Arizona, depositing the younger parts of the Escabrosa and Redwall Limestones. Osagean seaways extended to central and northern New Mexico depositing Kelly (35 m) and Espiritu Santo (35 m) Formations. The Espiritu Santo consists of subtidal to supratidal quartz sands one and carbonate rocks. Zuni Highlands and Pedernal Highlands formed two low islands. The end of the Tournaisian is marked by marine regression, regional uplift, and erosion. Major regional marine transgression in early Visean is represented by parts of Escabrosa Limestone of southern Arizona, massive encrinites of the Hachita Formation (107 m) in southwestern New Mexico, basin carbonate rocks of the lower part of the Rancheria Formation (46 m) in south-central New Mexico, and the subtidal Tererro Formation (18 m) in north-central New Mexico. The Cowles Member (10 m) of the Tererro Formation indicates that sedimentation ceased in northern and central New Mexico in late Visean time. In southwestern New Mexico, the Paradise Formation (134 m) represents shallow-marine sediments and ranges rom zone 15 into zone 19 (late Visean and Namurian). The Rancheria Formation (69 m) and the Helms Formation (50 m) of south-central New Mexico are deep-water facies of the Paradise Formation. Pennsylvanian sedimentary rocks in southern Arizona and in New Mexico truncate Mississippian sedimentary rocks of Namurian, Visean, and Tournaisian age. End_of_Article - Last_Page 671------------

A Record of Spruce (Pinaceae: Picea) from the Pleistocene of South-Central New Mexico

A Record of Spruce (Pinaceae: Picea) from the Pleistocene of South-Central New Mexico

The Role of Nectar Robbers and Pollinators in the Reproduction of Erythrina leptorhiza

The Role of Nectar Robbers and Pollinators in the Reproduction of Erythrina leptorhiza

Community succession in small bioherms of algae and sponges in the Lower Permian of New Mexico

Toomey. Donald F. & Cys. John M. 1979 01 15: Community succession in small bioherms of algae and sponges in the Lower Permian of New Mexico. Lethaia, Vol. 12. pp. 65–74. Oslo. ISSN 0024–1164. Small organic mounds outcrop in the Lower Permian Laborcita Formation of the northern Sacramento Mountains of southcentral New Mexico. These small organic structures, up to I'm in height and 3 m in diameter, are unique because they show a well developed vertical biolic zonation. This zonation consists of an initial pioneer community composed of small digitate or plumose colonies of algae and foraminifers (Stage 1). This is followed by a climax community that is first dominated by laminar colonies of the red alga Archaeolithophyllum (Stage 2). and followed by a terminal community composed of minor Archaeolithophyllum, erect heliosponges and brachiopods, dominated by the form Composita (Stage 3). Evidence suggests that the mounds initially developed in shallow water within an open lagoon but. with continued transgression and rapid deepening of the depositional environment. the biota responded to the changes. The organic buildups were killed off by sudden influx of clastics from a tectonically active nearby landmass.

The Systematics of the Bidens ferulaefolia Complex (Compositae)

Bidens ferulaefolia has been recognized as a species consisting of three varieties (var. ferulaefolia, var. foeniculifolia, and var. ludens) widely distributed from southwestern United States through Mexico and into Guatemala. Separation of these taxa was based on several highly variable morphological characters such as achene length, awn number, and degree of leaf dissection. These taxa were studied utilizing field and herbarium material, morphological data, cytotaxonomic studies, green- house and hybridization experiments, and comparative flavonoid chemistry. Results obtained from these investigations suggest that three species be recognized: B. fer- ulaefolia, B. carpodonta, and B. longistyla. Bidensferulaefolia occurs in disturbed habitats on the high plateau from Guanajuato in southcentral Mexico northwest into the foothills of the Sierra Madre Occidental in Chihuahua in northern Mexico. Bidens carpodonta inhabits disturbed areas in mountain valleys or on high plateaus, while B. longistyla is found in mountain valleys on gypsum and limestone outcrops, in the Sierra Madre Oriental of northeastern Mexico in the states of Nuevo Le6n and Coahuila. Morphological characteristics based on quantitative and qualitative fea- tures, such as style branch lengths and presence or absence of a red pigment in the flowering heads, are useful for distinguishing the three taxa. Cytotaxonomic data for these three species showed that B. ferulaefolia has a chromosome number of n = 10, while B. carpodonta and B. longistyla are both n = 12. Hybridization experiments at the intra- and interspecific levels confirmed that each species is reproductively isolated from the other two. Flavonoid comparisons of leaf and floral tissues from B. ferulaefolia, B. carpodonta and B. longistyla established the presence of species- specific compounds that would allow for the chemical separation of these three taxa. The two varieties previously recognized (var. foeniculifolia and var. ludens) are placed in synonymy with B. ferulaefolia, whereas B. carpodonta and B. longistyla are distin- guished as species. Finally, the geographical distribution formerly attributed to B. ferulaefolia was examined and was found to involve a number of related species. Throughout Mexico, particularly near the end of the rainy season in late September and October, one encounters population after population of grossly similar weedy Bidens annuals with large, yellow-rayed heads and pinnatisect leaves. In his classical studies of the genus Bidens in 1937 and 1955, Sherff treated all such plants with square stems and dimorphic achenes as a single species, B. ferulaefolia. Three varieties were recog- nized in both taxonomic treatments. Typical var. ferulaefolia was by far the most common, occurring in Arizona southeastward into Mexico to the states of Jalisco and Puebla, and rarely into Guatemala. This variety was characterized as having narrowly linear leaf segments and achenes which were 4-6 mm long with two aristae each. The latter were report- edly sometimes deciduous. In contrast, var. foeniculifolia had leaves