El objetivo de este trabajo fue evaluar caracteres anatómicos foliares que contribuyan a una mejor comprensión de la relación planta-ambiente y al desarrollo de tecnologías para el aprovechamiento sustentable y conservación de los bosques de esta región. Para ello se aplicaron técnicas histológicas convencionales sobre hojas de ejemplares de 36 especies recolectadas en la región chaqueña húmeda. Se determinaron densidades por mm-2 de células epidérmicas, estomas y tricomas, tipos de mesofilo, tipo y distribución de los tejidos vascular y de sostén. La mayoría de los árboles de la región en estudio presentan hojas hipostomáticas con mesofilo dorsiventral, elevada densidad de células epidérmicas (4000-7000/mm-2), una densidad intermedia de estomas (300-500/mm-2) y baja densidad de tricomas (< 35/mm-2). La comparación con los caracteres anatómicos foliares de los arbustos y árboles de las Provincias Biogeográficas Paranaense, de las Yungas y Chaqueña permite concluir que los rasgos más variables son la distribución de estomas y tipo de mesofilo. Las hojas xeromórficas son anfistomáticas, equifaciales y las mesomórficas son hipostomáticas, bifaciales. En el Distrito Chaqueño Oriental las hojas son predominantemente meso-xeromórficas, ya que a sus rasgos mesomórficos se suman otros xeromórficos como elevada densidad de células epidérmicas y abundante tejido esclerenquimático.
The genus Pseudognaphalium is one of the largest genera of the tribe Gnaphalieae (Asteraceae) with about 90 species with worldwide distribution. The vast majority of species are found in South, Central and North America, but some species also occur in Asia and Africa. This work includes the revision of 12 species of Pseudognaphalium from Chile, P. aldunateoides, P. cabrerae, P. cheiranthifolium, P. cymatoides, P. gayanum, P. lacteum, P. landbeckii, P. munoziae, P. psilophyllum, P. remyanum, P. tarapacanum, and P. viravira. A key is provided for their identification, as well as morphological description, illustration, geographic distribution and habitat, distribution maps, phenology, additional material examined, distinguishing characters and taxonomic affinities for each taxon. The new combination Pseudognaphalium cabrerae (S.E. Freire) S.E. Freire, N. Bayón, C. Baeza, Giuliano & C. Monti, is proposed. The following taxa are newly synonymized: Gnaphalium diminutivum, Pseudognaphalium perpusillum, with P. aldunateoides; G. canum, G. ulophyllum, P. moelleri with P. cymatoides; P. heterophyllum, P. heterotrichum, G. pseudohelichrysum, P. robustum with P. gayanum; P. glandulosum with P. psilophyllum; G. longifolium, G. subnudum, P. andicola, P. coquimbense, P. illapelinum, P. montevidense, P. pratense, with P. viravira.
The Briza complex comprises 23 species from South America, Mesoamerica and Europe. They constitute a monophyletic group because of the tendency of the spikelets to be dorsiventrally compressed. A cladistic analysis of the complex was performed using 32 characters from morphology. The terminal taxa were the species of the genera Briza, Calotheca, Microbriza, Poidium and Rhomboelytrum. Dactylis and Arrhenatherum were chosen to root the cladograms. Results of the cladistic analysis of the complex provide support for ( the ideas of Nicora and Rugolo 1981, Darwinianá ( ) . 23 1 , 279᎐309 : Briza, Calotheca, Microbriza, Poidium and Rhomboelytrum are supported as monophyletic groups. Within Briza, only the Chascolytrum group appears monophyletic, while the Briza and Uniolae groups are paraphyletic. Poidium ambiguum, sometimes placed in Poa, is considered here as Poidium.
Gamochaeta (tribe Gnaphalieae, Asteraceae) is composed of ca. 60 species primarily distributed in tropical and subtropical America. Within the tribe Gnaphalieae, the genus is characterized by capitula arranged in spikes or head-like clusters, few hermaphroditic central florets, truncate style branches with apical sweeping trichomes, pappus bristles connate at the base into a ring falling as a unit, and achenes with globose twin trichomes. Previous molecular phylogenetic studies have suggested the paraphyly of the genus, but have not provided a basis for redefining generic limits due to incomplete taxon sampling. To address this problem, DNA sequences from the plastid (trnL-F) and nuclear (ETS and ITS) genomes were analyzed from a broad taxon sample representing the full range of morphological variation known in the genus. Our results affirm that Gamochaeta is paraphyletic as presently circumscribed. Two clades can be recognized: one clade that includes the majority of the species currently assigned to Gamochaeta and a second clade that includes Gamochaetopsis, Stuckertiella and seven species of Gamochaeta. We present here a new circumscription of Gamochaeta, including two new combinations, Gamochaeta alpina and Gamochaeta peregrina, and the resurrection of Gamochaeta capitata. Our results also show Omalotheca supina, O. norvegica and O. sylvatica, which were placed by some authors in Gamochaeta or in Gnaphalium, form a monophyletic group distantly related to both genera.
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