Kinetic and thermodynamic control of C(sp2)-H activation enables site-selective borylation.

Catalysts that distinguish between electronically distinct carbon-hydrogen (C-H) bonds without relying on steric effects or directing groups are challenging to design. In this work, cobalt precatalysts supported by N-alkyl-imidazole-substituted pyridine dicarbene (ACNC) pincer ligands are described that enable undirected, remote borylation of fluoroaromatics and expansion of scope to include electron-rich arenes, pyridines, and tri- and difluoromethoxylated arenes, thereby addressing one of the major limitations of first-row transition metal C-H functionalization catalysts. Mechanistic studies established a kinetic preference for C-H bond activation at the meta-position despite cobalt-aryl complexes resulting from ortho C-H activation being thermodynamically preferred. Switchable site selectivity in C-H borylation as a function of the boron reagent was thereby preliminarily demonstrated using a single precatalyst.

Taxonomic revision of Muhlenbergia (Poaceae, Chloridoideae, Cynodonteae, Muhlenbergiinae) in Central America: phylogeny and classification.

A taxonomic treatment of 38 species of Muhlenbergia, a phylogeny based on analysis of six DNA sequence markers, and classification of Muhlenbergia for Central America (Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, Panama; and Campeche, Chiapas, Quintana Roo, Tabasco, and Yucatán, México) is given. With the support from a molecular phylogeny we describe Muhlenbergiasubg.Ramulosaesubgen. nov. In our treatment we place M.gigantea (younger name) as a synonym of M.mutica. Lectotypes are designated for the names Agrostismicrosperma Lag., Epicampesgigantea E. Fourn., Lamarckiatenella DC., Muhlenbergiaadspersa Trin., M.diversiglumis Trin., M.exilis E. Fourn., M.flabellata Mez, M.setarioides E. Fourn., Pereilemaciliatum E. Fourn., P.crinitumvar.cirratum E. Fourn., Podosemumciliatum Kunth, P.tenuissimum J. Presl, and Schellingiatenera Steud.

Reconfigurable Low-Voltage Hexagonal Boron Nitride Nonvolatile Switches for Millimeter-Wave Wireless Communications.

Recently, nonvolatile resistive switching memory effects have been actively studied in two-dimensional (2D) transition metal dichalcogenides and boron nitrides to advance future memory and neuromorphic computing applications. Here, we report on radiofrequency (RF) switches utilizing hexagonal boron nitride (h-BN) memristors that afford operation in the millimeter-wave (mmWave) range. Notably, silver (Ag) electrodes to h-BN offer outstanding nonvolatile bipolar resistive switching characteristics with a high ON/OFF switching ratio of 1011 and low switching voltage below 0.34 V. In addition, the switch exhibits a low insertion loss of 0.50 dB and high isolation of 23 dB across the D-band spectrum (110 to 170 GHz). Furthermore, the S21 insertion loss can be tuned through five orders of current compliance magnitude, which increases the application prospects for atomic switches. These results can enable the switch to become a key component for future reconfigurable wireless and 6G communication systems.

A phylogeny of the Triraphideae including Habrochloa and Nematopoa (Poaceae, Chloridoideae).

To investigate the evolutionary relationships among species of the tribe Triraphideae (including two monotypic genera, Habrochloa and Nematopoa), we generated a phylogeny based on DNA sequences from nuclear ribosomal (ITS) and four plastid markers (rps16-trnK, rps16 intron, rpl32-trnL, and ndhA intron). Habrochloa and Nematopoa form a clade that is sister to Neyraudia and Triraphis. Member of the Triraphideae have paniculate inflorescences, 3-veined, marginally ciliate lemmas, usually with hairy lateral veins, that are apically bifid and awned from between a sinus. A description of the Triraphideae and key to the genera is provided, and the biogeography is discussed, likely originating in Africa.

Seasonal Volatile Emission Patterns of the Endemic New Zealand Shrub Dracophyllum subulatum on the North Island Central Plateau.

Volatile organic compounds (VOCs) produced by plants are essential indicators of their physiological response to environmental conditions. But evidence of natural variation in VOC emissions and their contributing factors is still limited, especially for non-cultivated species. Here we explored the natural volatile emissions of Dracophyllum subulatum Hook.f., an endemic shrub to the North Island Central Plateau of New Zealand, and determined some environmental factors driving the plant's emissions. Volatile emissions of D. subulatum were measured on four separate occasions from December 2017 to September 2018 using the "push-pull" headspace sampling technique and analyzed using gas chromatography-mass spectrometry (GC-MS). D. subulatum was classified based on the volatiles measured on each sampling occasion using linear discriminant analysis (LDA). On each sampling occasion, we also recorded and compared ambient air temperature, herbivory damage, total soil nitrogen (N), available phosphorus (P), potassium (K), and soil moisture content. The relationship between environmental variables that differed significantly between sampling occasions and volatile emissions were estimated using generalized linear models (GLMs). Based on VOCs measured on each sampling occasion, we were able to distinguish different chemical profiles. Overall, we found that total emission and the relative proportions of all major chemical classes released by D. subulatum were significantly higher during summer. The GLMs reveal that differences in environmental factors between the four sampling occasions are highly associated with changing emissions. Higher temperatures in summer had a consistently strong positive relationship with emissions, while the impacts of soil moisture content, P and K were variable and depended on the chemical class. These results are discussed, particularly how high temperature (warming) may shape volatile emissions and plants' ecology.

Oxidative Addition of Aryl and Alkyl Halides to a Reduced Iron Pincer Complex.

The two-electron oxidative addition of aryl and alkyl halides to a reduced iron dinitrogen complex with a strong-field tridentate pincer ligand has been demonstrated. Addition of iodobenzene or bromobenzene to (3,5-Me2MesCNC)Fe(N2)2 (3,5-Me2MesCNC = 2,6-(2,4,6-Me-C6H2-imidazol-2-ylidene)2-3,5-Me2-pyridine) resulted in rapid oxidative addition and formation of the diamagnetic, octahedral Fe(II) products (3,5-Me2MesCNC)Fe(Ph)(N2)(X), where X = I or Br. Competition experiments established the relative rate of oxidative addition of aryl halides as I > Br > Cl. A linear free energy of relative reaction rates of electronically differentiated aryl bromides (ρ = 1.5) was consistent with a concerted-type pathway. The oxidative addition of alkyl halides such as methyl-, isobutyl-, or neopentyl halides was also rapid at room temperature, but substrates with more accessible ß-hydrogen positions (e.g., 1-bromobutane) underwent subsequent ß-hydride elimination. Cyclization of an alkyl halide containing a radical clock and epimerization of neohexyl iodide-d2 upon oxidative addition to (3,5-Me2MesCNC)Fe(N2)2 are consistent with radical intermediates during C(sp3)-X bond cleavage. Importantly, while C(sp2)-X and C(sp3)-X oxidative addition produces net two-electron chemistry, the preferred pathway for obtaining the products is concerted and stepwise, respectively.

A 313 plastome phylogenomic analysis of Pooideae: Exploring relationships among the largest subfamily of grasses.

In this study, we analyzed 313 plastid genomes (plastomes) of Poaceae with a focus on expanding our current knowledge of relationships among the subfamily Pooideae, which represented over half the dataset (164 representatives). In total, 47 plastomes were sequenced and assembled for this study. This is the largest study of its kind to include plastome-level data, to not only increase sampling at both the taxonomic and molecular levels with the aim of resolving complex and reticulate relationships, but also to analyze the effects of alignment gaps in large-scale analyses, as well as explore divergences in the subfamily with an expanded set of 14 accepted grass fossils for more accurate calibrations and dating. Incorporating broad systematic assessments of Pooideae taxa conducted by authors within the last five years, we produced a robust phylogenomic reconstruction for the subfamily, which included all but two supergeneric taxa (Calothecinae and Duthieeae). We further explored how including alignment gaps in plastome analyses oftentimes can produce incorrect or misinterpretations of complex or reticulate relationships among taxa of Pooideae. This presented itself as consistently changing relationships at specific nodes for different stripping thresholds (percentage-based removal of gaps per alignment column). Our summary recommendation for large-scale genomic plastome datasets is to strip alignment columns of all gaps to increase pairwise identity and reduce errant signal from poly A/T bias. To do this we used the "mask alignment" tool in Geneious software. Finally, we determined an overall divergence age for Pooideae of roughly 84.8 Mya, which is in line with, but slightly older than most recent estimates.

The Impact of a Virtual Radiology Medical Student Rotation: Maintaining Engagement During COVID-19 Mitigation.

INTRODUCTION: The purpose of this study is to introduce a virtual radiology rotation curriculum that is being used to safely maintain medical student and intern education and engagement with the Department of Radiology at Walter Reed National Military Medical Center during coronavirus disease 2019 (COVID-19) mitigation. MATERIALS AND METHODS: The curriculum is designed as a 4-week block with each week representing one of the four highest yield radiology subspecialties for medical students; neuroradiology, thoracic radiology, body radiology, and musculoskeletal radiology. A subspecialist radiologist from each section was identified as a primary mentor and tasked with designing a daily schedule for medical students and interns. The first 2 months of virtual rotators were surveyed to assess the effectiveness of the course. RESULTS: Thirty-five of 41 rotators responded to the survey, a response rate of 85%. Thirty-one of 35 (89%) of the rotators gave this virtual elective rotation a positive rating, with 16 trainees scoring the course as 4 out of 5 and 15 trainees selecting 5 out of 5. Four respondents selected 3 out of 5. Five out of 5 respondents who had experienced an in-person radiology elective rotation before this virtual rotation rated the virtual elective as more educational than the in-person rotation. We found the 4-week subspecialist mentor-based structure to be highly versatile, allowing us to simultaneously accommodate multiple groups of full or partial block rotators throughout COVID-19 mitigation. CONCLUSION: A virtual rotation curriculum is a viable method of maintaining medical student and intern education and engagement with the department of radiology during COVID-19 mitigation.

A phylogeny of species near Agrostis supporting the recognition of two new genera, Agrostula and Alpagrostis (Poaceae, Pooideae, Agrostidinae) from Europe.

Based on a molecular DNA phylogeny of three plastid (rpl32-trnK, rps16 intron, and rps16-trnK) and nuclear ITS regions investigating 32 species of Agrostidinae, we describe two new genera, Agrostula gen. nov. with a single species and Alpagrostis gen. nov. with four species; provide support for five species in a monophyletic Podagrostis; and include a small sample of 12 species of a monophyletic Agrostis s.s. (including the type and most species of Neoschischkinia), that separates into two clades corresponding to A. subg. Agrostis and A. subg. Vilfa. Agrostula differs from Agrostis in having leaf blades with pillars of sclerenchyma which are continuous between the adaxial and abaxial surface of the blades, dorsally rounded glumes with blunt to truncate and erose to denticulate apices, florets ½ the length of the glumes, lemmas equally wide as long, widest at (or near) apex, apices broadly truncate, irregularly 5 to 7 denticulate to erose, awnless, anthers longer than the lemmas, and rugose-papillose caryopses. Alpagrostis differs from Agrostis in having geniculate basally inserted awns and truncate lemma apices with lateral veins prolonged from the apex in (2)4 setae. The following eight new combinations are made: Agrostula truncatula, Agrostula truncatula subsp. durieui, Alpagrostis alpina, Alpagrostis alpina var. flavescens, Alpagrostis barceloi, Alpagrostis setacea, Alpagrostis setacea var. flava, and Alpagrostis schleicheri. In addition, we provide a key separating Agrostula and Alpagrostis from Agrostis s.s. and other genera previously considered as synonyms of Agrostis; lectotypify Agrostis alpina Scop., A. schleicheri Jord. & Verl., A. truncatula Parl., and A. truncatula var. durieui Henriq.; and neotypify A. setacea Curtis.

ResumenSobre la base de una filogenia molecular de ADN de tres regiones plastidiales (rpl32-trnK, rps16 intrón y rps16-trnK) e ITS nuclear de 32 especies de Agrostidinae, describimos dos nuevos géneros, Agrostula gen. nov. con una sola especie, y Alpagrostis gen. nov. con cuatro especies; mostramos el apoyo para las cinco especies dentro de Podagrostis monofilético; e incluimos una pequeña muestra de 12 especies de Agrostis s.s (que incluye el tipo y la mayoría de las especies de Neoschischkinia), este último dividido en dos subclados que corresponden a A. subg. Agrostis y A. subg. Vilfa. Agrostula se diferencia de otras especies de Agrostis por tener láminas foliares con haces de esclerénquima continuos entre las superficies adaxial y abaxial de los limbos, glumas de dorso redondeado y ápice embotado a truncado y eroso a denticulado, antecios de ½ de la longitud de las glumas, lemas tan anchas como largas, lo más ancho en o cerca del ápice, ápices anchamente truncados, irregularmente 5 a 7 denticulados o erosos, sin arista, anteras más largas que los lemas y cariopsis rugosa-papilosa. Alpagrostis se diferencia de otras especies de Agrostis por tener aristas geniculadas insertas basalmente y ápices de lema truncados con venas laterales que se prolongan en (2)4 arístulas apicales. Presentamos las siguientes ocho nuevas combinaciones: Agrostula truncatula, Agrostula truncatula subsp. durieui, Alpagrostis alpina, Alpagrostis alpina var. flavescens, Alpagrostis barceloi, Alpagrostis setacea, Alpagrostis setacea var. flava y Alpagrostis schleicheri. Además, proporcionamos una clave que separa Agrostula y Alpagrostis de Agrostis s.s. y otros géneros previamente considerados como sinónimos de Agrostis, lectotipificamos Agrostis alpina Scop., A. schleicheri Jord. & Verl., A. truncatula Parl. y A. truncatula var. durieui Henriq. y neotipificamos A. setacea Curtis.

Dapsone-induced DRESS after infliximab-induced vasculitis: a case of cerebral infarction in the context of multiple drug reactions.

Drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome is a life-threatening condition characterised by peripheral eosinophilia, rash and multi-organ failure arising several weeks after exposure to the culprit medication. Although rare, DRESS syndrome triggered by specific agents has been associated with specific genetic polymorphisms more prevalent in different ethnic groups, including an association between dapsone-induced DRESS and Human Leukocyte Antigen (HLA)-B:13*01, a single nucleotide polymorphism more prevalent in those of Asian descent. DRESS and drug-related vasculitis may affect any organ system including the central nervous system (CNS), usually manifesting as encephalitis, meningitis or embolic cerebrovascular accidents related to eosinophilic cardiac disease and thrombosis. CNS vasculitis is a much rarer complication of drug reactions that may manifest as multifocal ischemia on neuroimaging. In circumstances of drug-related vasculitides, treatment with high-dose corticosteroids may lead to rapid improvement and, ultimately, resolution of associated focal neurologic deficits.

The Geopolitics of Plant Pathology: Frederick Wellman, Coffee Leaf Rust, and Cold War Networks of Science.

During the Cold War, coffee became a strategically important crop in the global contest between the United States and the Soviet Union. The economies of many US allies in Latin America depended upon coffee. In the Cold War context, then, the coffee leaf rust (Hemileia vastatrix) became a geopolitical problem. Coffee experts in Latin America, which produced most of the world's coffee, began to prepare for an outbreak. In the 1950s, they built a global network of coffee experts. This network was sustained by US-led Cold War programs that promoted technical collaboration across the Global South, such as Harry Truman's Point Four programs. We explore the network's growth and evolution through one of its central figures, the American plant pathologist Frederick L. Wellman. This network has survived the end of the Cold War and evolved to reflect the new geopolitical context.

Effects of Two Invasive Weeds on Arthropod Community Structure on the Central Plateau of New Zealand.

Heather (Calluna vulgaris) and broom (Cytisus scoparius), originally from Europe, are the main invasive plants on New Zealand's North Island Central Plateau, where they threaten native flora and fauna. Given the strong link between arthropod communities and plants, we explored the impact of these invasive weeds on the diversity and composition of associated arthropod assemblages in this area. The arthropods in heather-invaded areas, broom-invaded areas, and areas dominated by the native species manuka (Leptospermum scoparium) and Dracohyllum (Dracophyllum subulatum) were collected and identified to order. During summer and autumn, arthropods were collected using beating trays, flight intercept traps and pitfall traps. Diversity indices (Richness, Shannon's index and Simpson's index) were calculated at the order level, and permutational multivariate analysis (PERMANOVA) was used to explore differences in order-level community composition. Our results show a significant variation in community composition for all trapping methods in both seasons, whereas invasive plants did not profoundly impact arthropod order richness. The presence of broom increased arthropod abundance, while heather was linked to a reduction. Under all possible plant pairings between heather, broom, manuka, and Dracophylum, the impact of neighbouring plant identity on arthropod community composition was further explored for the samples collected using beating trays. The results suggest that during plant invasion, arthropod communities are affected by neighbouring plant identity and that impacts vary between arthropod sampling methods and seasons.

Direct Observation of Transmetalation from a Neutral Boronate Ester to a Pyridine(diimine) Iron Alkoxide.

Transmetallation of the neutral boronate esters, (2-benzofuranyl)BPin and (2-benzofuranyl)BNeo (Pin = pinacolato, Neo = neopentylglycolato) to a representative pyridine(diimine) iron alkoxide complex, (iPrPDI)FeOEt (iPrPDI = 2,6-(2,6-iPr2-C6H3N=CMe)2C5H3N; R = Me, Et, SiMe3), to yield the corresponding iron benzofuranyl derivative was studied. Synthesis of the requisite iron alkoxide complexes was accomplished either by salt metathesis between (iPrPDI)FeCl and NaOR (R = Me, Et, SiMe3) or by protonation of the iron alkyl, (iPrPDI)FeCH2SiMe3, by the free alcohol R'OH (R' = Me, Et). A combination of magnetic measurements, X-ray diffraction, NMR and Mössbauer spectroscopies and DFT calculations identified each (iPrPDI)FeOR compound as an essentially planar, high-spin, S = 3/2 compound engaged in antiferromagnetic coupling with a radical anion on the chelate (S Total = 3/2; S Fe = 2, S PDI = 1/2). The resulting iron benzofuranyl product, (iPrPDI)Fe(2-benzofuranyl) was characterized by X-ray diffraction and in combination with magnetic measurements, spectroscopic and computational data, was identified as an overall S = 1/2 compound, demonstrating that a net spin-state change accompanies transmetallation (S Fe = 1, S PDI = 1/2). These findings may be relevant to further development of iron-catalyzed Suzuki-Miyaura cross-coupling with neutral boronate esters and alkoxide bases.

Seasonal and environmental variation in volatile emissions of the New Zealand native plant Leptospermum scoparium in weed-invaded and non-invaded sites.

The New Zealand tea tree Leptospermun scoparium (manuka) is widely known for the antimicrobial properties of its honey. Manuka is native to New Zealand, growing in a range of environments, including the Central Volcanic Plateau of the North Island, where it is currently threatened by the spread of exotic invasive weeds such as heather (Calluna vulgaris) and Scotch broom (Cytisus scoparius). Here, we characterise for the first time the aboveground volatile organic compounds (VOCs) produced by manuka in this area, during summer and winter seasons, in weed-invaded and non-invaded stands. We measured plant volatiles at four sites, each with a distinct combination of woody species: (1) conspecific stands of manuka; (2) manuka and another native species (Dracophyllum subulatum); and manuka with one of two European invasive plants, (3) heather or (4) Scotch broom. We also quantified herbivore damage on target manuka plants and analysed microclimatic variables (soil nutrients, air temperature and soil water content) to investigate their impact on volatile emissions. Our results reveal a strong seasonal effect on volatile emissions, but also significant differences between sites associated with biotic and abiotic changes partly driven by invasive plants. Overall, volatile emission rates from manuka were typically lower at sites where invaders were present. We point to several factors that could contribute to the observed emission patterns and areas of interest for future research to provide a comprehensive understanding of VOC emissions in nature. Given the vital role of volatile compounds in plant communication, we also recommend future studies to be performed in multiple seasons, with larger sample sizes and more study sites to expand on these findings and explore the ecological impacts of changes in VOC emissions during plant invasion.

Herbivory and Attenuated UV Radiation Affect Volatile Emissions of the Invasive Weed Calluna vulgaris.

Calluna vulgaris (heather) is an aggressive invasive weed on the Central Plateau, North Is., New Zealand (NZ), where it encounters different environmental factors compared to its native range in Europe, such as high ultraviolet radiation (UV) and a lack of specialist herbivores. The specialist herbivore Lochmaea suturalis (heather beetle) was introduced from the United Kingdom (UK) in 1996 as a biocontrol agent to manage this invasive weed. Like other plant invaders, a novel environment may be challenging for heather as it adjusts to its new conditions. This process of "adjustment" involves morphological and physiological changes often linked to phenotypic plasticity. The biochemical responses of exotic plants to environmental variables in their invaded range is poorly understood. The production and release of volatile organic compounds (VOCs) is essential to plant communication and highly susceptible to environmental change. This study therefore aimed to explore the VOC emissions of heather in response to different levels of UV exposure, and to feeding damage by L. suturalis. Using tunnel houses clad with UV-selective filters, we measured VOCs produced by heather under NZ ambient, 20% attenuated, and 95% attenuated solar UV treatments. We also compared VOC emissions in the field at adjacent sites where L. suturalis was present or absent. Volatiles produced by the same target heather plants were measured at four different times in the spring and summer of 2018-2019, reflecting variations in beetle's abundance, feeding stage and plant phenology. Heather plants under 95% attenuated UV produced significantly higher amounts of (E)-ß-farnesene, decanal, benzaldehyde, and benzeneacetaldehyde compared to 25% attenuated and ambient UV radiation. We also found significant differences in volatiles produced by heather plants in beetle-present versus beetle-absent sites on most sampling occasions. We also recorded a lower number of generalist herbivores on heather at sites where L. suturalis was present. Interactions between invasive plants, a novel environment, and the native communities they invade, are discussed.

New combinations and updated descriptions in Podagrostis (Agrostidinae, Poaceae) from the Neotropics and Mexico.

Based on morphological study and corroborated by unpublished molecular phylogenetic analyses, five grass species of high-mountain grasslands in Mexico, Central and South America, Agrostis bacillata, A. exserta, A. liebmannii, A. rosei, and A. trichodes, are transferred to Podagrostis and bring the number of species of this genus recognized in the New World to ten. The name Apera liebmannii is lectotypified and epitypified. We provide an updated genus description for Podagrostis, and updated species descriptions, images, and notes on the new combinations. The diagnostic characteristics differentiating Podagrostis from Agrostis are: a) palea that reaches from (2/3) ¾ to almost the apex of the lemma; b) florets that usually almost equal the length of the glumes or are at least ¾ the length of the glumes; c) rachilla extension present and emerging from under the base of the palea as a slender short stub (rudimentary or up to 1.4 mm long, sometimes obscure in most florets in P. rosei), smooth or scaberulous, glabrous or distally pilulose (hairs < 0.3 mm long); d) lemmas usually awnless, sometimes with a short straight awn 0.2-0.6 mm long, inserted medially or in the upper 1/3 of the lemma, not surpassing the glumes (awn well-developed, straight or geniculate and inserted in lower 1/3 of lemma, not or briefly surpassing glumes in P. rosei). We include a generic key to distinguish the species of Podagrostis from other similar genera in Latin America and a key to distinguish the species of Podagrostis now accepted as occurring in these areas.

ResumenBasado en estudios morfológicos y corroborado por datos no publicados de análisis filogenéticos, las cinco gramíneas de alta montaña de los pastizales en México, Centroamérica y Sur América Agrostis bacillata, A. exserta, A. liebmannii, A. rosei, y A. trichodes, son transferidos a Podagrostis incrementando a diez el número de especies en el nuevo mundo de este reconocido género. El nombre de Apera liebmannii también es lectotipificado y epitipicado. Proporcionamos una descripción actualizada del género Podagrostis, y descripciones actualizadas de las especies, imágenes y comentarios sobre las nuevas combinaciones. Las características diagnósticas que diferencian a Podagrostis de Agrostis son: a) pálea de 2/3-¾ hasta casi el ápice de la lemma; b) espiguillas, generalmente casi iguales en longitud a las glumas o de al menos ¾ la longitud de las glumas; c) extensión de la raquilla presente y emergiendo desde debajo de la base de la pálea como un trozo corto y delgado (desde rudimentario hasta de 1.4 mm de largo, a veces oscuro en la mayoría de los flósculos en P. rosei), liso o escabérulo, glabro o piloso distalmente (pelos < 0.3 mm de largo); d) lemmas generalmente sin arista, o a veces con arista corta y recta de 0.2­0.6 mm de largo, insertada medialmente o en el tercio superior de la lemma, sin sobrepasar las glumas (arista bien desarrollada, recta o geniculada e insertada en la parte inferior 1/3 de lemma, no o superando brevemente las glumas en P. rosei). Incluimos una clave para distinguir Podagrostis de otros géneros similares presentes en América Latina y una clave para distinguir las especies de Podagrostis ahora aceptadas por estar presentes en estas áreas.

Natural Variation in Volatile Emissions of the Invasive Weed Calluna vulgaris in New Zealand.

Invasive plants pose a threat to natural ecosystems, changing the community composition and ecological dynamics. One aspect that has received little attention is the production and emission of volatile organic compounds (VOCs) by invasive plants. Investigating VOCs is important because they are involved in vital ecological interactions such as pollination, herbivory and plant competition. Heather, Calluna vulgaris, is a major invasive weed in New Zealand, especially on the Central Plateau, where it has spread rapidly since its introduction in 1912, outcompeting native species. However, the chemical behaviour of heather in its invaded ranges is poorly understood. We aimed to explore the natural variation in volatile emissions of heather and the biotic and abiotic factors influencing them on the Central Plateau of New Zealand. To this end, foliar volatiles produced by heather at four different sites were collected and analysed using gas chromatography coupled to mass spectrometry. Soil properties, herbivory and other environmental data were also collected at each site to investigate their effects on VOC emissions using generalised linear models (GLMs). Our results reveal significant differences in VOC emissions between sites and suggest that soil nutrients are the main factor accounting for these differences. Herbivory and temperature had only a minor effect, while soil water content had no impact. Further studies are needed to investigate how these variations in the invasive plant's foliar volatiles influence native species.

Eriocoma valdesii, a new species from México (Poaceae, Stipeae).

Eriocoma valdesii sp. nov., is described and illustrated. The new species was found growing on calcareous rocky slopes and hillsides between 1700-2721 m in Coahuila, Nuevo León, San Luis Potosí, and Tamaulipas. The new species is morphologically similar to Eriocoma lobata but differs in having ligules (2-) 4.5-8.5 mm long with acute to narrowly acute and lacerate apices and florets with a sharp-pointed callus. In addition, we include a key to the species of Eriocoma in northeastern México.

ResumenSe describe e ilustra una nueva especie, Eriocoma valdesii sp. nov. La nueva especie se encontró creciendo en laderas calcáreas rocosas y laderas entre 1700­2721 m en Coahuila, Nuevo León, San Luis Potosí y Tamaulipas. La nueva especie es morfológicamente similar a Eriocoma lobata, pero difiere en tener lígulas de (2­) 4.5­8.5 mm de largo con ápices y flósculos agudos a estrechamente agudos y lacerados con un callo puntiagudo. Además, incluimos una clave para las especies de Eriocoma en el noreste de México.

A key to the North American genera of Stipeae (Poaceae, Pooideae) with descriptions and taxonomic names for species of Eriocoma, Neotrinia, Oloptum, and five new genera: Barkworthia, ×Eriosella, Pseudoeriocoma, Ptilagrostiella, and Thorneochloa.

Based on earlier molecular DNA studies we recognize 14 native Stipeae genera and one intergeneric hybrid in North America. We provide descriptions, new combinations, and 10 illustrations for species of Barkworthia gen. nov., Eriocoma, Neotrinia, Oloptum, Pseudoeriocoma gen. nov., Ptilagrostiella gen. nov., Thorneochloa gen. nov., and ×Eriosella nothogen. nov. The following 40 new combinations are made: Barkworthiastillmanii, Eriocomaalta, E.arida, E.arnowiae, E.bloomeri, E.bracteata, E.contracta, E.coronata, E.curvifolia, E.hendersonii, E.latiglumis, E.lemmonii, E.lemmoniissp.pubescens, E.lettermanii, E.lobata, E.nelsonii, E.nelsoniissp.dorei, E.nevadensis, E.occidentalis, E.occidentalisssp.californica, E.occidentalisssp.pubescens, E.parishii, E.parishiissp.depaupertata, E.perplexa, E.pinetorum, E.richardsonii, E.robusta, E.scribneri, E.swallenii, E.thurberiana, E.wallowaensis, ×Eriosellacaduca, Pseudoeriocomaacuta, P.constricta, P.editorum, P.eminens, P.hirticulmis, P.multinodis, Ptilagrostiellakingii, and Thorneochloadiegoensis. A key to the native and introduced genera of North American Stipeae, and an overview of the tribe in North America and worldwide are given. Lectotypes are designated for Eriocomacuspidata Nutt., Fendleriarhynchelytroides Steud., Stipabloomeri Bol., Stipacoronata Thurb., Stipamembranacea Pursh, Stipamormonum Mez, Stiparichardsonii Link, and Stipawilliamsii Scribn. Achnatherum s.s. and Piptatherum s.s. are now restricted to Eurasia and the Mediterranean/Asia, respectively.

ResumenBasados en estudios anteriores de ADN molecular, reconocemos 14 géneros nativos de Stipeae y un híbrido intergenérico en América del Norte. Se presentan descripciones, nuevas combinaciones, y 10 ilustraciones para las especies de Barkworthia gen. nov., Eriocoma, Neotrinia, Oloptum, Pseudoeriocoma gen. nov., Ptilagrostiella gen. nov., Thorneochloa gen. nov. y ×Eriosella nothogen. nov. Se realizan las siguientes 40 nuevas combinaciones: Barkworthiastillmanii, Eriocomaalta, E.arida, E.arnowiae, E.bloomeri, E.bracteata, E.contracta, E.coronata, E.curvifolia, E.hendersonii, E.latiglumis, E.lemmonii, E.lemmoniissp.pubescens, E.lettermanii, E.lobata, E.nelsonii, E.nelsoniissp.dorei, E.nevadensis, E.occidentalis, E.occidentalisssp.californica, E.occidentalisssp.pubescens, E.parishii, E.parishiissp.depaupertata, E.perplexa, E.pinetorum, E.richardsonii, E.robusta, E.scribneri, E.swallenii, E.thurberiana, E.wallowaensis, ×Eriosellacaduca, Pseudoeriocomaacuta, P.constricta, P.editorum, P.eminens, P.hirticulmis, P.multinodis, Ptilagrostiellakingii y Thorneochloadiegoensis. Se presenta una clave para los géneros nativos e introducidos de las especies norteamericanas, y una visión general de la tribu en América del Norte y en todo el mundo. Se designan lectotipos para Eriocomacuspidata Nutt., Fendleriarhynchelytroides Steud., Stipabloomeri Bol., Stipacoronata Thurb., Stipamembranacea Pursh, Stipamormonum Mez, Stiparichardsonii Link y Stipawilliamsii Scribn. Achnatherum s.s. y Piptatherum s.s. ahora están con distribución restringida- a Eurasia y el Mediterráneo/Asia, respectivamente.

Structural implications of the paramagnetically shifted NMR signals from pyridine H atoms on synthetic nonheme FeIV=O complexes.

Oxoiron(IV) motifs are found in important intermediates in many enzymatic cycles that involve oxidations. Over half of the reported synthetic nonheme oxoiron(IV) analogs incorporate heterocyclic donors, with a majority of them comprising pyridines. Herein, we report 1H-NMR studies of oxoiron(IV) complexes containing pyridines that are arranged in different configurations relative to the Fe = O unit and give rise to paramagnetically shifted resonances that differ by as much as 50 ppm. The strong dependence of 1H-NMR shifts on the different configurations and orientation of pyridines relative to the oxoiron(IV) unit demonstrates how unpaired electronic spin density of the iron center affects the chemical shifts of these protons.