Recent Workers Research Articles

Molecular Anions Perspective.

This Perspective attempts to shed light on developments in the theoretical and experimental study of molecular anions highlighting more recent workers in the field. The species I discuss include (i) valence-bound (singly and multiply charged) anions including atmospheric, catalytic, superhalogen, interfacial, and more; (ii) dipole- and correlation-bound anions including their role as doorways to other states and their appearance "in space", and (iii) metastable anions focusing on tools needed for their theoretical treatment. I also briefly discuss angular distributions of photodetached electrons and their growing utilization in experiments and theory. A recurring theme is the dependence of electron binding energies (EBEs) on the surrounding environment. Some anions that are nonexistent as isolated species evolve to be stable but with small EBEs when weakly solvated (e.g., as in a cluster or at an air-solvent interface). Others existing in isolation only as metastable species become stable when the underlying molecular framework contains one or more positively charged group (e.g., protonated side chains in a peptide) that generates a stabilizing Coulomb potential. On the other hand, a destabilizing Coulomb potential between/among negative sites in a multiply charged anion decreases the EBEs of each such site and generates a repulsive Coulomb barrier that can affect stability.

Allocation of Salamandra auriculata Holbrook, 1838, with a new species of swamp-dwelling dusky salamander (Plethodontidae: Desmognathus) from the Atlantic Coastal Plain

Most swamp-dwelling dusky salamanders of the genus Desmognathus from the Coastal Plain were long treated as a single species (Desmognathus auriculatus) ranging from east Texas to southeastern Virginia. This taxon concept was based on the name Salamandra auriculata Holbrook, 1838 with type locality Riceboro, Liberty County, Georgia and a type series that could not be located by later authors. Recent workers have been unable to locate or verify swamp-dwelling populations from east Texas and western Louisiana, which appear to be extirpated and may not have represented a distinct taxon from co-occurring lineages of D. conanti. Recent molecular phylogenies have supported at least four distinct species-level taxa within D. auriculatus. Populations from the Gulf Coastal Plain in eastern Louisiana, Mississippi, and southwestern Alabama were recently described as D. valentinei Means, Lamb, and Bernardo, 2017 and D. pascagoula Pyron, O'Connell, Lamb, and Beamer, 2022. This leaves two remaining species-level lineages with uncertain taxonomy and nomenclature: D. auriculatus A (Alabama, Florida, and Georgia), and D. auriculatus B/C (Georgia, South Carolina, and North Carolina), both of which occur near the type locality. We recently located a specimen at the Muséum national d'Histoire naturelle in Paris (MNHN 0.4675) that we concluded is one of Holbrook's syntypes and designated it as the lectotype, but without allocation. Here, we use linear morphometrics to confidently allocate it to D. auriculatus A, bolstered by examination of three historical topotypic collections. This requires a new name for D. auriculatus B/C, which we describe as D. valtos sp. nov. (suggested common name: Carolina Swamp Dusky Salamander) from Otter Creek, Craven County, North Carolina. Other related and sympatric species of Desmognathus remain to be described from the Atlantic Coastal Plain and adjacent Piedmont of the southeastern United States.

The interplay between basement fabric, rifting, syn‐rift folding, and inversion in the Rio do Peixe Basin, NE Brazil

AbstractThe Rio do Peixe Basin is part of a series of aborted Cretaceous rifts formed within the Proterozoic Borborema Province, onshore NE Brazil in response to rifting between Africa and South America. The basin is remarkably well‐imaged and comprises fault‐bounded depocentres, the main ones being the NE‐oriented Brejo das Freiras and the E–W‐oriented Sousa half‐grabens. These grabens and their bounding faults are influenced by Neoproterozoic basement shear zones and present a complex framework of secondary normal faults and folds. Recent workers also interpret large reverse faults and regional post‐rift shortening driven by far‐field stresses from the Andes. For those reasons, the basin represents an ideal setting to investigate the multiphase history of rift basins. We thus combine borehole‐calibrated 2D and 3D seismic and magnetic data with section restoration and numerical modelling to investigate the architecture and evolution of this basin. We aim to understand: (i) the controls of the basement fabric in 3D fault architecture and kinematics and (ii) how syn‐rift faults controlled the geometry and development of fault‐related folds. By doing this, we also investigate the timing, kinematics, and magnitude of inversion in the basin to explore its multiphase history. We demonstrate that (i) the basement fabric controlled not only the strike of faults but also their geometry and polarity at depth, (ii) folds in the syn‐rift sequence are attributed simply to syn‐rift extension along stepped and/or curved faults, and (iii) inverted and/or reverse faults occur within the basin, but these are minor and appear to have formed during rifting. We explain this minor inversion by a change in plate kinematics related to the onset of the nearby transform margin to the north. These results have implications for understanding the 3D evolution of oblique grabens, the role of structural inheritance, and the recognition of inversion‐ versus extension‐related folds in rift basins worldwide.

Daily Stress and Sleep Associations Vary by Work Schedule: A Between- and Within-Person Analysis in Nurses

Nurses experience poor sleep and high stress due to demanding work environments. Night shift work may exacerbate stress-sleep associations. We examined bidirectional associations between daily stress and sleep, and moderation by shift worker status and daily work schedule. 392 nurses (92% female, mean age = 39.54) completed 14 days of sleep diaries and actigraphy, plus daily assessments of stress and work schedule upon awakening. Nurses were classified as recent night shift workers if they worked 1+ night during the past 14 days. Greater daily stress predicted shorter diary sleep duration and lower diary sleep efficiency. Shorter diary and actigraphy sleep duration and lower diary sleep efficiency predicted higher next-day stress. Compared to recent night workers, day workers had higher stress after nights with shorter sleep. Associations did not vary by daily work schedule. Sleep disturbances and stress may unfold in a toxic cycle and are prime intervention targets among nurses.

Nomenclature of supra-generic units within the Family Scincidae (Squamata).

The modern classification of skinks is based on a nomenclature that dates to the 1970s. However, there are a number of earlier names in the family group that have been overlooked by recent workers. These names are identified and their validity with respect to the International Code of Zoological Nomenclature investigated, along with their type genera. In most cases, use of these names to supplant junior synonyms in modern day use is avoidable by use of the Reversal of Precedence articles of the Code, but the names remain available in case of future divisions at the tribe and subtribe level. Other names are unavailable due to homonymy, either of their type genera or the stems from similar but non-homonymous type genera. However, the name Egerniini is replaced by Tiliquini, due to a limited timespan of use of Egerniini. A new classification of the Family Scincidae is proposed, providing a more extensive use of Code-regulated levels of classification, including tribes and subtribes, and a detailed synonymy provided for each taxonomic unit.

Racial and ethnic differentials in COVID-19-related job exposures by occupational standing in the US.

Researchers and journalists have argued that work-related factors may be partly responsible for disproportionate COVID-19 infection and death rates among vulnerable groups. We evaluate these issues by describing racial and ethnic differences in the likelihood of work-related exposure to COVID-19. We extend previous studies by considering 12 racial and ethnic groups and five types of potential occupational exposure to the virus: exposure to infection, physical proximity to others, face-to-face discussions, interactions with external customers and the public, and working indoors. Most importantly, we stratify our results by occupational standing, defined as the proportion of workers within each occupation with at least some college education. This measure serves as a proxy for whether workplaces and workers employ COVID-19-related risk reduction strategies. We use the 2018 American Community Survey to identify recent workers by occupation, and link 409 occupations to information on work context from the Occupational Information Network to identify potential COVID-related risk factors. We then examine the racial/ethnic distribution of all frontline workers and frontline workers at highest potential risk of COVID-19, by occupational standing and by sex. The results indicate that, contrary to expectation, White frontline workers are often overrepresented in high-risk jobs while Black and Latino frontline workers are generally underrepresented in these jobs. However, disaggregation of the results by occupational standing shows that, in contrast to Whites and several Asian groups, Latino and Black frontline workers are overrepresented in lower standing occupations overall and in lower standing occupations associated with high risk, and thus may be less likely to have adequate COVID-19 protections. Our findings suggest that greater work exposures likely contribute to a higher prevalence of COVID-19 among Latino and Black adults and underscore the need for measures to reduce potential exposure for workers in low standing occupations and for the development of programs outside the workplace.

Mature vs Young Working Students: Similarities, Differences, and Drivers of Graduation and Dropout

The high dropout rate among working students in higher education in Portugal, including both those who are older and at a mature stage in their professional careers and those who are young and recent workers, is one of the main concerns of educational policy. Identifying the drivers of the academic pathway for these students is essential to promote successful education and increase labour productivity and business competitiveness. Using an extensive longitudinal database of personal, course, and employment variables of 1,561 working students from a Portuguese higher education institution, we perform a duration analysis to determine and compare the factors that drive the dropout and graduation risks of mature and young working students in higher education. The results show that, in general, young working students are more positively influenced by financial aid, their motivation for the course, and the desire to find a new qualified professional career, while mature working students depend more on social and academic integration. The accumulation of knowledge/skills in the 'out of class' experience seems to contribute positively to academic performance.

Intergenerational Exploitation of Filipino Women and Their Japanese Filipino Children: “Born out of place” Babies as New Cheap Labor in Japan

This paper focuses on the Japanese Filipino children as “born out of place” babies of migrant Filipino mothers and recent young migrant workers in Japan’s labor market. I present the unique position of Japanese Filipino children and their Filipino mothers as an example of intergenerational exploitation of migrants in Japanese society. The existence of Japanese Filipino children mirrors intersectional discrimination in Japanese society; they were born as a consequence of the inequality based on gender and ethnicity between the Philippines and Japan, then they were ignored by the Japanese state as “illegitimate” children, and now they their Filipino mothers have begun to be exploited as “unskilled labor” in Japan.

EMPLOYMENT AFTER NORMAL RETIREMENT AGE: EMPLOYERS’ MOTIVES AND EXPERIENCES

Due to population aging, older workers in developed countries are working much longer than previous cohorts. Some older workers even extend their careers beyond normal retirement age – or the age that is traditionally associated with retirement. While earlier work has studied employees’ motives and experiences while working after normal retirement age, motives and experiences of employers remain unexplored. Understanding employers’ perspectives is imperative for a better grasp of employees’ opportunity structures and labor market dynamics. This is especially relevant in countries with mandatory retirement systems, since here employer and employee need to negotiate a new contract after normal retirement age. I study employers’ motives to and experiences with employing older workers after normal retirement age using data from a 2017 survey among 1,312 Dutch employers. The Netherlands has mandatory retirement regulations but is also seeing an increase in employment rates after normal retirement age. Results show that 54% of employers have, in recent years, employed one or more older workers beyond their normal retirement age. This is especially common in education. 70% of employers are very positive about their previous experiences with employing older workers after normal retirement age, mostly because they had rehired older workers with unique knowledge and experience. However, employers also hardly ever took the initiative for such employment arrangements, instead leaving it to the older workers to show the desire to continue working. Although employers are largely positive, they see it as a limited phenomenon, and do not consider it a solution to labor shortages.

Revision of the early crocodylomorph Trialestes romeri (Archosauria, Suchia) from the lower Upper Triassic Ischigualasto Formation of Argentina: one of the oldest‐known crocodylomorphs

AbstractTrialestes romeri (Reig) is an early crocodylomorph from the Ischigualasto Formation (late Carnian – early Norian; Ischigualasto – Villa Unión Basin, Argentina) and one of the oldest‐known members of this clade. Two specimens of this species are known, the holotype (PVL 2561) and a referred specimen (PVL 3889), both consisting of associated cranial and postcranial remains. These specimens are incomplete and poorly preserved thus leading previous authors to propose different phylogenetic hypotheses for the species. Trialestes romeri was originally interpreted as a basal dinosaur, subsequently considered to be a crocodylomorph with some dinosaurian characters (e.g. mesotarsal ankle joint, functionally tridactyl pes), and even proposed as a chimera representing two different genera. Some recent workers have mentioned and discussed Trialestes, but none have described it in detail or included it in a quantitative phylogenetic analysis. Here, we describe in detail all the material assignable to the species and test its phylogenetic relationships using a comprehensive data matrix focused on early archosaurs. We support the referral of PVL 3889 to Trialestes and reject the presence of a mesotarsal ankle joint in this specimen. We recovered Trialestes within Crocodylomorpha, closer to Crocodyliformes than Pseudhesperosuchus, Hesperosuchus, Dromicosuchus and Sphenosuchus. Several stratigraphical units worldwide approximately coeval with the Ischigualasto Formation, have also yielded early crocodylomorph remains, such as the upper Santa María (Brazil), Pekin (USA), and lower Maleri (India) formations. However, the crocodylomorph specimens recovered from those units are more incomplete, possess uncertain phylogenetic affinities, or are part of chimaerae. Therefore, Trialestes represents the most completely known of the earliest non‐crocodyliform crocodylomorph taxa known to date.

Characterizing Quantitative Variation in the Glossopodia of Three Western North AmericanIsoëtesSpecies

Abstract One of the challenges when working with the genus Isoetes is the scarcity of in-depth comparative analyses of its morphological characters. This paucity of analyses relates in part to the long-held conclusion that most of the characteristics associated with the traits of the genus aside from spore morphology, are too variable to be informative. As a result, our understanding of morphological variability among species of Isoetes is underdeveloped. Recent workers have attempted to address this deficiency by examining the glossopodia of the ligule, a structure unique among living taxa to Isoetes and its sister genus, Selaginella. The glossopodium is embedded in the adaxial surface of the microphyll, and has shown evidence of interspecific variability in the few studies in which it has been examined. However, these prior works were limited to qualitative comparisons. The present study compares 3D reconstructions of the glossopodia of three species, Isoetes howellii, I. bolanderi and I. nuttallii, usi...

Curves of Small Genus on Certain K3 Surfaces

Recent workers [1, 3] have proved density theorems about the rational points on K3 surfaces of the form $$ V:\;X_0^4+cX_1^4=X_2^4+cX_3^4 $$ for certain non-zero values of c. Their arguments depend on the presence of at least two pencils of curves of genus 1 on V. Unfortunately the values of c for which the argument works are constrained by the need to exhibit explicitly a rational point on V which satisfies certain extra conditions; these in particular require it to lie outside the four obvious rational lines on V. It is therefore natural to ask whether there are other curves of genus 0 or 1 defined over Q on V. In the case c = 1 there are known to be infinitely many such curves (see [2]), and for general rational c the quadratic form Q on the Néron–Severi group whose value is the self-intersection number takes the values 0 and -2 infinitely often. Naively one might expect the case c = 1 to be typical; but this is not so. The main object of this paper is to prove the following result.

The Anatomy and Phylogenetic Relationships of "Pelorosaurus" becklesii (Neosauropoda, Macronaria) from the Early Cretaceous of England.

The sauropod dinosaur “Pelorosaurus” becklesii was named in 1852 on the basis of an associated left humerus, ulna, radius and skin impression from the Early Cretaceous (Berriasian-Valanginian) Hastings Beds Group, near Hastings, East Sussex, southeast England, United Kingdom. The taxonomy and nomenclature of this specimen have a complex history, but most recent workers have agreed that “P.” becklesii represents a distinct somphospondylan (or at least a titanosauriform) and is potentially the earliest titanosaur body fossil from Europe or even globally. The Hastings specimen is distinct from the approximately contemporaneous Pelorosaurus conybeari from Tilgate Forest, West Sussex. “P.” becklesii can be diagnosed on the basis of five autapomorphies, such as: a prominent anteriorly directed process projecting from the anteromedial corner of the distal humerus; the proximal end of the radius is widest anteroposteriorly along its lateral margin; and the unique combination of a robust ulna and slender radius. The new generic name Haestasaurus is therefore erected for “P.” becklesii. Three revised and six new fore limb characters (e.g. the presence/absence of condyle-like projections on the posterodistal margin of the radius) are discussed and added to three cladistic data sets for Sauropoda. Phylogenetic analysis confirms that Haestasaurus becklesii is a macronarian, but different data sets place this species either as a non-titanosauriform macronarian, or within a derived clade of titanosaurs that includes Malawisaurus and Saltasauridae. This uncertainty is probably caused by several factors, including the incompleteness of the Haestasaurus holotype and rampant homoplasy in fore limb characters. Haestasaurus most probably represents a basal macronarian that independently acquired the robust ulna, enlarged olecranon, and other states that have previously been regarded as synapomorphies of clades within Titanosauria. There is growing evidence that basal macronarian taxa survived into the Early Cretaceous of Europe and North America.

Reinstatement of Dermacentor bellulus (Acari: Ixodidae) as a Valid Species Previously Confused with D. taiwanensis and Comparison of All Parasitic Stages.

Re-examination of Dermacentor taiwanensis Sugimoto, 1935 specimens in the United States National Tick Collection revealed that two morphologically distinct Dermacentor species were identified under this name. One of them corresponds to Sugimoto's description of D. taiwanensis, while another species is identical to Schulze's Dermacentor bellulus (Schulze, 1935). The latter species has not been considered valid by recent workers. D. bellulus is reinstated here as a valid species and all its stages are redescribed. The adults of D. taiwanensis are also redescribed, and its immature stages are described for the first time. Males and females of D. bellulus can be distinguished from those of D. taiwanensis by the shape of the conscutum and scutum, color pattern, genital structures, size of the palpi and cornua, and the spurs of coxa I. Nymphs of D. bellulus can be distinguished from those of D. taiwanensis by the shape of the scutum, basis capituli, and the hypostomal dentition. Larvae of D. bellulus can be differentiated from those of D. taiwanensis by the shape of the basis capituli, and the degree of development of the auriculae and spur on palpal segment III ventrally. D. bellulus has been recorded from China, Japan, Nepal, Taiwan, and Vietnam; adults have been collected from wild boars, bears, panda, dog, and human; the immature stages are known from rodents, hares, ferret-badger, and bamboo-partridge. D. taiwanensis is found in China, Taiwan, and Vietnam; adults have been collected from wild boars; the immature stages are known from rodents, hares, mustelids, and domestic dog.

A new shelf-to-basin timeline for the Middle Permian (Guadalupian) Capitan Depositional System, West Texas and Southeastern New Mexico, USA

The correlation of the Rader Limestone Member of the Bell Canyon Formation to its shelf equivalent has varied over the years. Some models have equated it with the Seven Rivers Formation, and others to the Yates Formation, or a position straddling both units. More recent workers have used sequence stratigraphic models to refine this shelf-to-basin correlation, placing the “lower” part of the Rader Limestone Member in the Y3 high frequency sequence within the Yates Formation. Despite the presence of bentonites in both the Rader Limestone Member and the Yates Formation, and the potential to add a numerical age datum to the sequence stratigraphic hierarchy, geochemical tephrochronologic techniques have not yet been applied to the deposits. To address these issues, apatite phenocryst trace element chemistry was determined by electron microprobe analysis for samples from three bentonites collected from outcrop localities in Guadalupe Mountains National Park and two from the Gulf PDB-04 research well. Results are interpreted to indicate a correlation between a bentonite 16.5m above the base of the Rader at Back Ridge in the Patterson Hills of Guadalupe Mountains National Park, and one at 1956ft core depth in the PDB-04 core. Careful examination of the gamma-ray log for the well indicates that the 1956ft interval is in the Y3 high frequency sequence of Osleger and Tinker (1999). Further refinement can be made to the third cycle set of this high frequency sequence. Determining whether the bentonite at Back Ridge is in the “lower” or “upper” part of the Rader Member will require additional work. This correlation links the primary reference section for the basal through middle Capitanian Stage being established at Back Ridge with the shelf defined sequence stratigraphic framework. The sample from the Rader is the focus of U-Pb radioisotopic dating (Nicklen et al. in preparation) and would provide the first shelf-to-basin absolute age datum for the Capitan depositional system.

Deductive inference on the plate height equation of ultra performance liquid chromatography

In recent years, separation and analysis workers have made considerable progress on ultra performance liquid chromatography (UPLC). A lot of separation works have been completed which have never been done before. But the theory about chromatographic dynamics of UPLC from the beginning up to now, is remaining in 1950's. Some people explain the principle of UPLC by the van Deemter equation, but this is not right. In this paper, the dynamic process of UPLC has been studied. According to the chromatographic dynamics principle and starting from the heat conduction equation, the plate height equation of UPLC including the influence of mobile phase friction heat production has been deduced as follows: [Formula: see text]. The last item on the right represents the contribution of mobile phase friction heat. When the linear velocity of mobile phase is lower, the contribution of mobile phase friction heat tending to become zero, the plate height equation is reduced to the Horvath and Lin equation. When the linear velocity of mobile phase is high, the temperature difference between the column axial center and edge is directly proportional to the mobile phase linear speed square, and the contribution of thermal effect will largely increased. In this paper, the author clearly pointed out that the column efficiency of UPLC has a direct bearing on the column diameter. Using fine diameter column is helpful to implement column efficiency. Too high mobile phase velocity will lead to the column efficiency collapsed.

Blood, bulbs, and bunodonts: on evolutionary ecology and the diets of Ardipithecus, Australopithecus, and early Homo.

Beginning with Darwin, some have argued that predation on other vertebrates dates to the earliest stages of hominid evolution, and can explain many uniquely human anatomical and behavioral characters. Other recent workers have focused instead on scavenging, or particular plant foods. Foraging theory suggests that inclusion of any food is influenced by its profitability and distribution within the consumer's habitat. The morphology and likely cognitive abilities of Ardipithecus, Australopithecus, and early Homo suggest that while hunting and scavenging occurred, their profitability generally would have been considerably lower than in extant primates and/or modern human hunter-gatherers. On the other hand, early hominid diet modelers should not focus solely on plant foods, as this overlooks standard functional interpretations of the early hominid dentition, their remarkable demographic success, and the wide range of available food types within their likely day ranges. Any dietary model focusing too narrowly on any one food type or foraging strategy must be viewed with caution. We argue that early hominid diet can best be elucidated by consideration of their entire habitat-specific resource base, and by quantifying the potential profitability and abundance of likely available foods.

Improving the Psychosocial Work Environment at Multi-Ethnic Workplaces: A Multi-Component Intervention Strategy in the Cleaning Industry

Global labour migration has increased in recent years and immigrant workers are often recruited into low status and low paid jobs such as cleaning. Research in a Danish context shows that immigrants working in the cleaning industry often form social networks based on shared languages and backgrounds, and that conflict between different ethnic groups may occur. This paper evaluates the impact of a multi-component intervention on the psychosocial work environment at a multi-ethnic Danish workplace in the cleaning sector. The intervention included Danish lessons, vocational training courses, and activities to improve collaboration across different groups of cleaners. Interviews about the outcome of the intervention were conducted with the cleaners and their supervisor. The Copenhagen Psychosocial Questionnaire was used as a supplement to the interviews. The results suggest that the psychosocial work environment had improved after the intervention. According to the interviews with the cleaners, the intervention had led to improved communication, trust, and collaboration. These findings are supported by the questionnaire where social support from supervisor and colleagues, social community, trust, and teamwork seem to have improved together with meaning of work, rewards, and emotional demands. The design of the intervention may provide inspiration for future psychosocial work environment interventions at multi-ethnic work places.

The dog-faced water snakes, a revision of the genus Cerberus Cuvier, (Squamata, Serpentes, Homalopsidae), with the description of a new species

Snakes of the genus Cerberus Cuvier, 1829 occupy a unique, widespread coastal distribution and have a salt-tolerant physiology that allows members of the genus to move across a wide range of salinities from full salt water to freshwater. Cerberus nomenclature is revised based upon morphology and builds on previous molecular studies. Three species have been recognized by recent workers, here we recognize five species: the South Asian C. rynchops (Schneider 1799); the Southeast Asian-Philippine C. schneiderii (Schlegel 1837), a new combination; the freshwater Philippine endemic C. microlepis Boulenger 1896; the Australopapuan C. australis (Gray 1842); and a new species from Micronesia. We also select a lectotype for Homalopsis schneiderii Schlegel based upon a figure published in 1837 and restrict the type locality for this species to Timor. Evidence is also presented for a population of Cerberus australis in Indonesia, west of Weber’s Line.

Phylogenetic Relationships of Asclepias (Apocynaceae) Inferred from Non-coding Chloroplast DNA Sequences

Milkweeds ( Asclepias s. l., Apocynaceae) are characteristic perennial herbs of grasslands in North America and Africa that have long served as models for studying the evolutionary ecology of plant reproduction and plant defense. Generic circumscription of Asclepias has been long debated with recent workers favoring delimitation on geographic grounds; Asclepias s. s. is limited to the Americas and only seg- regate genera are recognized for African species. A widely used system introduced by Woodson classifies North American Asclepias into nine subgenera, with the largest subgenus, Asclepias , further divided into eight series. We investigated the phylogeny of Asclepias using three non- coding loci from the plastid genome: rpl16 intron, trnC GCA -rpoB spacer, and the adjacent trnS GCU -trnG UUC spacer and trnG UUC intron. Parsimony, likelihood, and Bayesian analyses were conducted to evaluate hypotheses of continental and taxonomic monophyly. Hypothesis tests were conducted under the parsimony and likelihood criteria. We found moderate support for the monophyly of American Asclepias s. s. and for all but one representative of African Asclepias s. l. Within the Amerian clade, South American species are strongly supported as monophyletic and derived from North American ancestors. Only one of Woodson's 17 infrageneric taxa was found to be monophyletic. Monophyly of more than one half of the remaining 16 taxa could be statistically rejected using a conservative a level. Our results are consistent with taxonomic restric- tion of Asclepias to American species and single colonization events from Africa to North America and North America to South America. They also point to a need for major restructuring of infrageneric classification and future revsionary work.