Search

Broom snakeweed (Gutierrezia sarothrae) and threadleaf snakeweed (G. microcephala) are suffrutescent plants found in many parts of western US rangelands and are possibly toxic to grazing livestock. The toxic components are not known, but it has been suggested that the diterpene acids may be both toxic and abortifacient. One hundred sixty-two samples of snakeweed were collected from 55 locations in Colorado, Oklahoma, New Mexico, Texas, Wyoming and Utah and were taxonomically classified. Samples were analyzed by GC-MS in a chemophenetic analysis and grouped into individual chemotypes based on diterpene acid content. The GC-MS profiles were found to be diverse showing at least eight different chemotypes. From each of the chemotypes the major diterpene acids were isolated and characterized by IR, MS and NMR spectroscopy. Twenty-one diterpenoids were identified and found to be a mix of furano, lactone, di-acid and esters of labdane, ent-labdane and chlerodane acids and alcohols. Only four of the 21 compounds isolated had been previously reported as occurring in G. sarathorea or G. microcephala, while another eight compounds were previously reported from other Gutierrezia or related species. Nine of the isolated diterpenoids have not been previously reported and their structure elucidation is reported.

During the revision of South American species of Gutierrezia (Asteraceae, Astereae) taxonomic novelties were established: (1) two new varieties were described, Gutierrezia mandonii var. anomala from northwestern Argentina, and Gutierrezia isernii var. nivea from central and western Argentina; and (2) the species Gutierrezia pulviniformis was included as a new synonym of Gutierrezia spathulata.

Se describen los efectos de la UV-B sobre la síntesis de pigmentos fotosintéticos (clorofila total, clorofila a, clorofila b, carotenoides), protectores (compuestos absorbentes de UV-B) y azúcares solubles (glucosa, fructosa y sacarosa) en cinco variedades de quinoa de diferentes orígenes geográficos. En general, se demuestra que las variedades reaccionan desplegando diferentes estrategias para protegerse de la radiación UV-B. Estas estrategias pueden ser de tipo morfológico, fisiológico y/o bioquímico. Una respuesta común, observada en las cinco variedades fue el incremento en el contenido de compuestos absorbentes de UV-B, lo que puede interpretarse como un “escudo químico” de protección para el aparato fotosintético frente al exceso de energía proveniente de la radiación quese aplica a las plantas.

Asteraceae es la familia de plantas vasculares mas diversaa nivel mundial y la mas numerosa de Argentina, incluyendo26% de especies endemicas. Muchas asteraceas son pioneras, facilitandoel establecimiento de otras especies, y varias se han utilizadoen restauracion. Dada la importancia de conocer las caracteristicas delas semillas y de la germinacion para su utilizacion en proyectos derestauracion, se indaga sobre aspectos fisiologicos basicos de la germinacionde Gutierrezia solbrigii Cabrera y Senecio subulatus D. Donex Hook. & Arn. var. erectus Hook. & Arn., arbustos endemicos deArgentina distribuidos en zonas aridas de Patagonia. El material provinode la Reserva Provincial Auca Mahuida (NE de Neuquen), enel Distrito Fitogeografico de Payunia (ecotono Monte-Estepa). Alli,la actividad hidrocarburifera ha generado areas degradadas dondeestas especies podrian utilizarse para revegetacion. Se evaluo el porcentajede germinacion (G), el tiempo medio de germinacion (TMG)y los dias hasta el inicio de la germinacion (IG) de un control y detratamientos pre-germinativos: estratificacion humeda fria de 15 dias(EHF15), escarificacion mecanica con lija (EML) para las dos especies,y estratificacion humeda fria de 30 dias (EHF30) y escarificacionmecanica con bisturi (EMB) para S. subulatus. Para los tratamientos losporcentajes de germinacion fueron elevados (G. solbrigii: 77% EHF15,81% EML; S. subulatus: 88% EHF15, 89% EHF30, 84% EML, 94%EMB) y similares a los controles (G. solbrigii: 82%,S. subulatus: 88%).Solo se registraron diferencias entre EMB y EML para S. subulatus: Ge IG fueron mayores en EMB y el TGM menor, posiblemente porquecon EML las semillas no son escarificadas uniformemente. En conclusion,ambas especies carecen de mecanismos de dormicion bajo lascondiciones experimentales, lo que sumado al hecho de que crecen enambientes disturbados y son endemicas, las hace excelentes candidataspara trabajos de restauracion ecologica.

Gutierrezia leucantha Cabrera, a species previously included in the synonymy of Gutierrezia gillesii Griseb., is reinstated as a distinct species. A morphological description is presented with information on distribution and habitat. A key to distinguish this species from its congeners with white ray florets is provided.

Durante el transcurso de la revisión de las especies sudamericanas de Gutierrezia, hemos podido hallar nombres que requieren tipificación. Luego del análisis de los protologos y especímenes de herbario, hemos designado ocho lectótipos y un neótipo para nueve nombres del género Gutierrezia. Además, se asignó la categoría de hólotipo a un especimen. Se provee una discusión detallada para cada nombre.

Research into plant breeding systems enables the evaluation of whether seed production depends on pollination agents and gene flow mechanisms within and among populations. This aids, in turn, the estimation of the appropriate population sizes needed to maintain both genetic and species' diversity. Little is known about plant reproductive biology in the Monte Desert (Patagonia, Argentina), a habitat threatened by desertification as a result of human impact. The mating systems, flowering phenologies and pollinator networks were studied in five representative plant species of the Monte Desert. The mating systems studied ranged from anemophilous pollen dispersion in the dioecious Atriplex lampa, to a gradient of dependence on pollinators, from the less dependent (facultative self-compatible) Gutierrezia solbrigii and two Larrea spp. (L. divaricata and L. cuneifolia) to the most dependent Grindelia chiloensis (self-incompatible). Flowering phenology was restricted to spring and coincided with pollinator abundance. Solitary bees were the main pollinator group, but beetles, flies and butterflies were also important. The four insect-pollinated species were moderately generalist, but they maintained their own pollinator assemblage. Coleopterans depended more on Grindelia chiloensis and dipterans on Gutierrezia solbrigii. Lepidopterans frequently visited Gutierrezia solbrigii and Larrea divaricata, whereas hymenopterans visited both Larrea spp. more frequently. The studied plant species are ecologically important, not only as resources for a wide range of pollinator species but also for other insects. The Monte Desert is a very disturbance-sensitive environment and, as these plant species hardly show vegetative regeneration, sexual reproduction is essential for their survival. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 161, 190–201.

Previous molecular investigations of the phylogenetic relationship for Xylothamia employed exemplar taxa and indicated its affiliation is either with the Gutierrezia or the Ericameria alliances. The present 3' ETS and ITS nrDNA gene phylogenies yielded the unexpected result that Xylothamia is polyphyletic. Species within its circumscription are placed into two well-supported evolutionary lineages with other genera of Astereae. Of nine species of Xylothamia, four species plus Gundlachia constitute one clade. The other five species are placed in a sister clade with several other genera including Amphiachyris, Bigelowia, Euthamia, Gutierrezia, and others. Except for X. johnstonii and X. palmeri, these five species of Xylothamia have little affinity for one another or for other genera in the same clade. Morphological similarities in foliar features between certain species in both lineages are possibly from a convergence resulting in adaptation to arid habitats. Such similarities were also the basis, in part, for their taxonomic treatment within Xylothamia or their earlier affiliation with Ericameria, which has similar features. The uncharacteristic leaf form in Xylothamia purpursii has a pattern of adaptation considerably different from its allies. Whether the Xylothamia-containing clades are related to Solidaginineae or represent an independently derived lineage remains equivocal because this outcome rested with the choice of data and optimality criteria.

We hypothesise that genotypic differences in transpiration and root growth in the southern and northern populations of Gutierrezia sarothrae are driven by growing season vapour pressure deficit (VPD) and that ecotypic differentiations are linked to corresponding variations in tissue and leaf water relations. Seedlings from an Idaho (ID) and a Texas (TX) seed source were grown either in an open nursery (full sunlight) or under shade. There were no population differences in transpiration, root growth and tissue water relation parameters when the plants were grown under the shade. However, significant population differences were observed in the plants grown in the open where VPD was substantially higher. Transpiration in the TX population increased twice as rapidly as the ID population in response to rising potential evapotranspiration (PET). In addition, the TX plants grew longer and larger lateral roots than the ID plants when both populations were grown in the open. Moreover, the TX plants had more elastic cell walls (lower bulk cell elastic modulus, E) and were able to maintain leaf turgor at lower relative water content than the ID plants when grown in the open. Similar changes in tissue water relation parameters were observed in the New Mexico (NM) and the ID seedlings subjected to soil water deficit. Cell elastic modulus (E), relative water content at zero turgor (RWC0) and apoplastic water fraction (Wa) were significantly lower in the NM population than in the ID population in response to soil water deficit, suggesting a higher turgor maintenance ability in the NM population. RWC0 was highly correlated with E in the NM (r=0.92, P

Se describe e ilustra Gutierrezia tortosae Ratto & Adr. Bartoli, una nueva especie de Argentina. Se asemeja a Gutierrezia mandonii (Sch. Bip.) Solbrig por presentar xilopodio, por la forma de las hojas y por el color amarillo de las flores liguladas, pero difiere de ella por tener tallos erectos y rígidos, hojas erectas y capítulos menores. Se presenta una clave para diferenciarla de las especies que habitan en el noroeste de Argentina.

A new species, Gutierrezia chubutensis (Asteraceae, Astereae, Solidagininae) from Florentino Ameghino in Chubut Province, Argentina is described and illustrated. It is distinct from its congeners in Patagonia because of its height (over 50 cm), larger elliptical leaves and numerous heads with yellow flowers and involucre terete or terete-turbinate. A key to differentiate the new species from the other Patagonian species of Gutierrezia is provided.

Hydraulic lift occurs in some deep-rooted shrub and herbaceous species. In this process, water taken up by deep roots from the moist subsoil is delivered to the drier topsoil where it is later reabsorbed by shallow roots. However, little is known about the existence of hydraulic lift in shallow-rooted xeric species. The objectives of this study were 1) to ascertain whether hydraulic lift exists in Gutierrezia sarothrae (broom snakeweed), a widespread North American desert species with a shallow root system, grown in pot and field conditions and 2) if it does, how much water can be transferred from the subsoil to the 30 cm topsoil during the night. Snakeweed seedlings were transplanted in buried pots allowing the deeper roots to grow into the subsoil 30 cm below the surface. Soil water content inside and outside of the pot was measured seasonally and diurnally with time domain reflectometry technique (TDR). An increase in water content was detected in the pot after the plant was covered for 3 h by an opaque plastic bag during the day, suggesting hydraulic lift from deeper depths and exudation of water into the drier topsoil. Root exudation was also observed on native range sites dominated by snakeweed. Water efflux in the pot was 271 g per plant per night. which was equivalent to 15.3% of the extrapolated, porometer-derived whole-plant daily transpiration. Hydraulic lift observed in Gutierrezia improved water uptake during the day when evaporative demand is high and less water is available in the topsoil. We concluded that hydraulic lift might help snakeweed to alleviate the effect of water stress.

We hypothesize that predominance of Gutierrezia sarothrae in the rangeland plant community depends on its ability to take up water more effectively from soil depths below 30 cm. Gutierrezia seedlings grown in 30-cm-deep pots were allowed to develop deep lateral roots out of pots into subsoil. The deep laterals were then excised and photosynthesis and stomatal conductance of the test plants measured before and after root pruning. Photosynthesis (A) and stomatal conductance (g) were at least 49% greater (P < .05) before than after root pruning. Photosynthesis and g were more affected by the removal of four deep roots 30 cm below the surface than by the removal of four shallow roots in the top 30 cm of soil. The soil water extraction patterns in Gutierrezia plants grown in 60-cm soil columns were determined for the upper 30 cm and 30 to 60 cm of soil. Water extraction was significantly greater (P < .05) from the wetter, lower section of the soil column than from the drier, upper column. Higher photosynthesis...

Type specimens of two names (Euphorbia sparsiflora A. Heller, Euphorbiaceae, Gutierrezia ionensis Lunell, Asteraceae) have been discovered, superseding recent lecto- and neotypifications.

The aerial parts of Gutierrezia resinosa gave 15 new diterpenes including 12 labdanes and three nerylgeraniol derivatives. The structures were elucidated by high field NMR spectroscopy.

The extract of the aerial parts of Gutierrezia espinosae gave 11 new and two known labdanes as well as five new nerylgeraniol derivatives. The structures were elucidated by high field 1 H NMR spectroscopy. The chemotaxonomic aspects are discussed briefly.

Gutierrezia ameghinoi Speg., a species from the Argentinean Patagonia, is resurrected. Its geographical distribution and habitat are described. A key to distinguish G. ameghinoi from co-occurring relatives is included. The species is illustrated for the first time.

En el marco de la revisión taxonómica del género Gutierrezia para Sudamérica fue hallada una nueva especie de Argentina, caracterizada por sus tallos con la porción basal postrada, enraizante en los nudos, capítulos con involucro turbinado y flores liguladas blancas. Se describe e ilustra la especie encontrada en el Departamento de Tunuyán de la Provincia de Mendoza (Argentina), y se incluye una clave para diferenciarla de las especies afines.

A colored painting from the Sesse and Mocifio expedition serves as the holotype for the validly published name Grindelia angustifolia DC. ex Dunal, 1819 (= Grindelia dunalii Sprengel, nom. nov., 1825; non Grindelia angustifolia Kunth, in HBK, 1818). The illustration represents the species heretofore identified as Keerlia linearifolia DC., 1836 (= Gutierrezia alamanii A. Gray, nom. nov., 1852; non Gutierrezia linearifolia Lagasca & Segura, 1816), which occurs in the south-central Mexican states of Mexico and Morelos. Gutierrezia dunalii (Sprengel) Nesom, comb. nov., is proposed as the earliest valid name for this species. Gutierrezia megalocephala (Fernald) Nesom is proposed for a closely related entity (Gutierrezia alamanii var. megalocephala (Fernald) Lane = Xanthocephalum megalocephalum Femald). The Sess6 and Mocifio expedition to New Spain (1787-1803) recorded many interesting observations, especially regarding the flora of Mexico. For a description of the expedition and its aims, travels, collections, paintings, and in particular its botanical accomplishments, see articles by McVaugh (1977, 1980, 1987, 1990, 1998) and a recent summary and update by Bartholomew and McVaugh (1997). Plant collections from the expedition are housed at a number of European herbaria as documentation for various early reports and names, but the paintings made in situ by expedition artists also provided the basic information for descriptions of new taxa. A. P. De Candolle and contemporaries proposed approximately 370 new specific names based wholly or in part on these paintings. Considerations regarding the formal typification of these taxa are outlined by Bartholomew and McVaugh (1997) and McVaugh (1998). The original set of paintings is now housed under the name of the Torner Collection of Sesse and Mocifio Biological Illustrations at the Hunt Institute for Botanical Documentation (Carnegie Mellon University, Pittsburgh). Some of these remarkably detailed paintings have remained without corroboration or reevaluation of their initial identifications, if such were ever made. We examined one of them (Torner No. 0884; Fig. 1), which includes on the same sheet two species of Asteraceae tribe Astereae, the left-hand one annotated by De Candolle as "Lemerya anthemoides" and the other as "Grindelia angustifolia." It is assumed that the plants were encountered by the expedition in Mexico, as surmised from the identities of the plants depicted. The Grindelia illustration served as the basis for a formal description of the species in a publication by Michel-Felix Dunal in 1819 (see nomenclature below). The left-hand plant is white-rayed, a species of Aphanostephus. Details at the top of the illustration, showing white ray flowers, disc corollas, and achenes, are from this plant. The slender taproot of annual duration, pinnatifid leaves, basally unexpanded disc corollas, and achenes with a conspicuous coronal pappus are features of A. ramosissima DC. var. ramosus (DC.) Turner & Birdsong (Turner, 1984), which occurs over a wide area of central Mexico, from Durango to San Luis Potosf and south to MichoacAn, Guerrero, Morelos, and Veracruz. The yellow-rayed plant (on the right-hand side) represents the species heretofore identified as Gutierrezia alamanii A. Gray, which is known from the south-central Mexican states of Mexico and Morelos (Lane, 1985). Salient features shown in the illustration are these: a basally ascending stem arising from a fibrous-rooted rhizome; leaves linear-oblanceolate without a well-defined petiolar portion, 1nerved, entire, primarily basally disposed but continuing up the stem; several relatively large heads (compared to other species of Gutierrezia) with conspicuous yellow rays (18, 21, and 23 rays, respecNovoN 10: 67-70. 2000. This content downloaded from 157.55.39.215 on Wed, 31 Aug 2016 04:26:17 UTC All use subject to http://about.jstor.org/terms

Restriction site mutations analysis using 18 restriction endonucleases for chloroplast DNA's from North American Gutierrezia has led to a generic circumscription which is somewhat different from those previously proposed. Molecular data agree with a recent taxonomic treatment of Lane (1982, 1985), which transferred the x = 4 species from Xanthocephalum and submerged Greenella into Gutierrezia, but they do not support the submersion of the monotypic genus Thurovia. Thurovia is closely related as a sister group to Amphiachyris and should be resegregated from Gu- tierrezia. The study indicated that Xanthocephalum with x = 6 is very distantly related to Gutierrezia, even though Xanthocephalum has often been treated as part of the Xanthocephalum-Gutierrezia complex. Xanthocephalum is, in contrast, very closely related to Grindelia, which also has a base chromosome number of x = 6. Traditional species of Gutierrezia, G. californica, G. grandis, G. microcephala, G. sarothrae, G. serotina, and G. texana, constitute a closely related cluster and are well-separated from other purported members of the genus. Gutierrezia californica s. str. and G. bracteata should be separated again as distinct species. The herbaceous species, G. sericocarpa and G. sphaerocephala, appear to be the most primitive in the genus.

The close systematic affinities between the composite genera Haplopappus and Chrysothamnus, including different points of contact with "intergeneric" hybrids, are reviewed. The Mohave Desert has several shrubby representatives of each genus, and at census sites from the east-central New York Mountains to buttes at the extreme western end of the desert, north-facing granitic slopes at the foothills of mountain ranges support four Haplopappus species (H. cuneatus, H. laricifolius, H. linearifolius and H. cooperi) and one Chrysothamnus (C. teretifolius). These five species occupy "distributional niches" represented as ranges and areas of dominance on the habitat plane of slope angle and proportion of rocks in the substrate. Central desert sites have four species (excluding C. teretifolius); peripheral desert sites always include C. teretifolius rather than H. laricifolius and support two to four species depending on the size and isolation of the suitable habitat area. Species may occupy different positions on the habitat gradient depending on species number at the site, moisture availability, and in particular competition from other species. C. teretifolius appears to be favored when population turnover rates are high, either in disturbed sites or on natural islands of habitat. THE MOJAVE DESERT vegetation is characterized by large, tree-like yuccas (Yucca brevifolia), by certain large shrubs such as Lycium, Larrea and Ephedra, and in particular by a host of smaller (?2-i m) woody perennial shrubs among which the family Asteraceae is predominant. At lower (and drier) elevations, generally below 1,000 m, such genera as Ambrosia, Acamptopappus, Encelia and Machaeranthera are encountered, and at higher elevations species of Tetradymia, Gutierrezia, Artemisia and Brickellia become common. Two composite genera in particular, Haplopappus and Chrysothamnus, have near

The aerial parts of Gutierrezia lucida afforded three new diterpenic acids, all closely related to agathic acid and those of G. mandonii also three diterpenic acids, which again are labdane derivatives. The structures were elucidated by spectroscopic methods and some chemical transformations. The roots of these species and of a further one only contain triterpenes and no acetylenes. The chemotaxonomic situation is briefly discussed.

Six new ent -labdanes were isolated from the aerial parts of Gutierrezia species and nine from Happlopappus pectinatus . Four neoclerodanes and a friedolabdane were obtained from the aerial parts of Haplopappus paucidentatus . From the Grindelia species, in addition to known derivatives of grindelic acid, an arabinoside was isolated. The absolute configuration of the ent -labdanes was determined by transformation of grindelic acid to methyl-6-oxo-7,8-dihydrogrindelate where the configuration was established by the positive Cotton effect. From Solidago petradoria a new abietane derivative was isolated.

Twelve known and nine new highly oxygenated flavonoid aglycones, some of which exhibit 2′-oxygenation, were isolated from Gutierrezia grandis .

The ethyl acetate extract of the aerial parts of Gutierrezia sphaerocephala afforded, in addition to one coumarin, 10 known and two new flavonoids. The structures were elucidated by spectroscopic methods. The new, flavonoids are 5,3′,4′,5′-tetrahydroxy-6,7-dimethoxyflavone and 5,7,4′-trihydroxy-6,3′-dimethoxyflavanone.

Five new diterpene glycosides, two arabinopyranosides and three xylopyranosides were isolated from Gutierrezia sphaerocephala . One of the arabinosides contained a tiglate ester at the 3′-position of the sugar moiety.

Thirteen flavonoids, including three new compounds, were isolated from Gutierrezia grandis. The structures of the new compounds were 3,5,7,3′,4′-pentahydroxy-6,8-dimethoxyflavone, 5,7,3′-trihydroxy-3,6,8,4′,5′-pentamethoxyflavone and 5,7,3′,5′-tetrahydroxy-3,6,8,4′-tetramethoxyflavone 3′-O-glucoside.

An investigation of the aerial parts of Gutierrezia dracunculoides afforded, in addition to known compounds, three new labdane derivatives, all related to lambertianic acid, 17-hydroxy- and 17-acetoxylambertianic acid and 7α- hydroxylambertianic acid, two esterified and three highly oxygenated flavones, 5,7,4′-trihydroxy-3,3′-dimethoxy- flavone-4′- O - [2-methylbutyrate] and isovalerate, 3′,5′-dihydroxy-3,5,6,7,8,4′-hexamethoxyflavone, 5,3′,5′-trihydroxy- 3,6,7,8,4′-pentamethoxyflavone and 5,7,3′,5′-tetrahydroxy-3,6,8,4′-tetramethoxyflavone. The structures were elucidated by spectroscopic methods and a few chemical transformations.

Two new diterpenes, 3α-angeloyloxy-18-hydroxy-13-furyl- ent -labda-8(17)-ene and 3α-hydroxy-18-angeloyloxy- 13-furyl- ent -labda-8(17)-ene and an only recently reported third diterpene, 3α, 18-dihydroxy-13-furyl- ent -labda-8(17)-ene, were isolated from the leaves of Gutierrezia grandis . Their structures were determined by mass spectral, IR, 1 H NMR and 13 C NMR data was well as chemical evidence.

The aerial parts of Gutierrezia resinosa afforded two highly oxygenated flavones 5,4′-dihydroxy-3,6,7,8,3′-pentamethoxyflavone and 5,3′,4′-trihydroxy-3,6,7,8-tetramethoxyflavone. The structures were elucidated by spectroscopic methods and confirmed by X-ray diffraction techniques. These flavones showed significant inhibition in vitro against the cells derived from human epidermoid carcinoma of the nasopharinx (KB).

(1) Larvae of the two tortricid lepidopterans, Synnoma lynosyrana and Synalocha gutierreziae, form silk cases that tie together a significant proportion of the photosynthetic stems and leaves of the common rangeland perennial, Gutierrezia sarothrae, which are toxic to cattle. (2) These insects were significantly more abundant in cattle-grazed plots than in ungrazed plots of the Sevilleta National Wildlife Refuge, located in central New Mexico, USA. (3) Using these herbivores as the experimental manipulation of the plant, measurements were made of photosynthetic area and proximate reproduction of plants with both tied and control (non-tied) branches. In within-plant comparisons, tied branches had significantly less photosynthetic area than control branches. The number of flowers/ branch, flowers/capitulum, seeds/branch and seeds/capitulum were all significantly greater for control than for tied branches. However, seeds produced by tied branches germinated more rapidly and at a higher percentage than seeds from control branches over the same time period. (4) The onset of senescence occurred on smaller volume plants in the ungrazed, high larval abundance plots than in the grazed, low larval abundance plots. (5) The results suggest that, at natural levels of tissue loss, Synnoma and Synalocha can seriously affect both the photosynthetic area and the reproduction of individual plants, and can thus potentially affect Gutierrezia population dynamics.

Amphiachyris is a North American genus of two species, A. dracunculoides and A. amoena. Related to Gutierrezia, it has in the past been placed in synonymy under that genus and also under Xanthocephalum. The generic status of A mphiachyris, as recognized by Solbrig, is accepted. Chromosome counts for both species and two species of Gutierrezia are reported. Counts of n = 4 for A. amoena and A. dracun- culoides and n 5 and n = 8 for G. texana are new. Preliminary chromatographic results indicate the presence of sulfated flavonoids in Amphiachyris. The genus Amphiachyris is composed of two annual species, one of which is restricted to the limestone-derived clay soils of the Edward's Plateau region of central Texas. The other, a very weedy species, is distributed widely on black prairie soils in the midwestern United States with scat- tered localities known as far east as South Carolina (Fig. 1). The distri- butions of Amphiachyris and of the annual species of Gutierrezia overlap throughout much of their ranges; these taxa are also quite similar in gross morphology. It is not surprising, therefore, that the taxonomic placement of Amphiachyris has been altered several times by various work- ers. The purpose of the present study is to evaluate the status of the taxon, using morphological, cytological and chemical methods.

Gutierrezia comprises sixteen North American species; two have two varieties each. Thurovia and Greenella are congeners of Gutierrezia, five taxa formerly of Xanthocephalum are mem- bers of Gutierrezia, and G. argyrocarpa is a distinct species. Characteristics shared by all taxa include alveolate receptacles that are pubescent with uniseriate trichomes that are swollen medially and long-attenuate apically, disc corollas that are clavate or funnelform and glabrous (except in one species), disc style-branch appendages that are linear with penicillate collecting hairs, achenes that are clavate or cylindrical and pubescent, and a pappus of scales that are united and/or greatly reduced in some taxa. In North America, the genus is distributed from the area of Mexico City northward throughout the Sierras Madres Occidental and Oriental, the central plateau of Mexico, and the central and western United States northward to western Canada. Habitats are well-drained, high montane slopes, mesic or semi-arid grasslands, and deserts.

Xanthocephalum, Gutierrezia, Greenella, Gymnosperma, Amphiachyris, and Thurovia have been variously treated with regard to their generic limits by several authors in the last 3 decades. The generic delimitation presented here is based on a thorough re-evaluation of all 26 known North American members of these genera. The data obtained in the study strongly support the following disposition of the taxa, which differs from all previous treatments. Xanthocephalum (x = 6), a genus of montane areas in western Mexico and the southwestern United States, contains five species (one with three varieties) and is more closely related to Grindelia and Olivaea than to Gutierrezia and its allies. Gutierrezia (x = 4) encompasses seventeen specific and infraspecific taxa in North America, including not only the eight taxa recognized for it by Solbrig, but also five taxa formerly of Xanthocephalum, and the genera Greenella and Thurovia (the last resulting in Gutierrezia triflora, comb. nov.). The genus thus constituted ranges from central Mexico north and west through the central and western United States to Saskatchewan. Amphiachyris (n = 4 or 5) with two grassland species of Texas and central United States, and the monotypic Gymnosperma (x = 8), which ranges from northern Guatemala to Texas and westward to Arizona, are closely allied to Gutierrezia. The taxonomic problem presented by the group of genera that unfortunately have been called the "Xanthocephalum complex" is one of generic rather than specific circumscription. The genera concerned, besides Xanthocephalum, are Amphiachyris, Amphipappus, Greenella, Gutierrezia, Gymnosperma, and Thurovia. Taxonomic histories have been provided by Solbrig (1960a, 1960b, 196 1a, 196 1b, 1966), Ruffin (1974), Porter (1943), and Lane (1979, 1980b). A very brief summary of the several evaluations is as follows. A number of workers, including Bentham (1873) and Gray (1852, 1853, 1880a, 1880b, 1883), recognized the affinity of most of these genera, but for the most part maintained them as distinct entities. Shinners (1950) united all except Amphipappus and Thurovia under Xanthocephalum. Solbrig (1960b) again segregated them, while Ruffin (1974, 1977a) recommended that Gutierrezia and Greenella be submerged in Xanthocephalum and that Amphiachyris, Amphipappus, Gymnosperma, and Thurovia be considered distinct. It might seem unnecessary to reconsider this taxonomic problem in view of the several treatments already in the literature. However, data that have accumulated even since the most recent of these suggest that such a reconsideration is in order. None of the previous studies included every species of each genus; further, the various authors changed only the taxonomic rankings of whole, historically constituted genera. I wished

One approach to the problem of deducing the genealogy of a set of organisms is to propose several hypotheses using different procedures, based on different evolutionary inferences. Such an approach was followed here, and four different phylogenies were constructed, three of them computer built. Consistency with independently obtained phenetic, cytological, and phytogeographical data was used to select the most probable phylogenetic tree among the four. It is shown that the most probable tree is one constructed under the assumption that character states found close to the mean and/or modal values for the genus are primitive. It is also shown that certain phylogenetic conclusions obtain in all four phylogenies.