177,079 research outputs found
Lycopodiella alopecuroides (L.) Cranfill
No full textGuyana, Cuyuni-Mazaruni Region: 2-3 km. W of Maipuri Falls, Karowrieng R., LAT (5°41' N); LONG (60°15' W); ALT (570 - 600), "Savanna. Growing amongst tall grasses and sedges in wet savanna. Plants with prostate stem rooted at frequent intervals and firmly attached to substrate. Fertile branches tall, erect.
Ferns diversified in the shadow of angiosperms
No full textThe rise of angiosperms during the Cretaceous period is often portrayed as coincident with a dramatic drop in the diversity and abundance of many seed-free vascular plant lineages, including ferns(1-5). This has led to the widespread belief that ferns, once a principal component of terrestrial ecosystems(6), succumbed to the ecological predominance of angiosperms and are mostly evolutionary holdovers from the late Palaeozoic/early Mesozoic era. The first appearance of many modern fern genera in the early Tertiary fossil record implies another evolutionary scenario; that is, that the majority of living ferns resulted from a more recent diversification(7-10). But a full understanding of trends in fern diversification and evolution using only palaeobotanical evidence is hindered by the poor taxonomic resolution of the fern fossil record in the Cretaceous(11). Here we report divergence time estimates for ferns and angiosperms based on molecular data, with constraints from a reassessment of the fossil record. We show that polypod ferns (>80% of living fern species) diversified in the Cretaceous, after angiosperms, suggesting perhaps an ecological opportunistic response to the diversification of angiosperms, as angiosperms came to dominate terrestrial ecosystems
Unraveling the phylogeny of polygrammoid ferns (Polypodiaceae and Grammitidaceae): exploring aspects of the diversification of epiphytic plants
No full textWe explore the phylogeny of the polygrammoid ferns using nucleotide sequences derived from three plastid loci for each of 98 selected species. Our analyses recovered four major monophyletic lineages: the loxogrammoids, two clades consisting of taxa restricted to the Old World, and a largely neotropical clade that also includes the pantropical Grammitidaceae. The loxogrammoid lineage diverges first and is sister to a large clade comprising the three remaining species-rich lineages. One paleotropical clade includes the drynarioid and selligueoid ferns, whereas the second paleotropical clade includes the platycerioids, lepisoroids, microsoroids, and their relatives. The grammitids nest within the neotropical clade, although the sister taxon of this circum-tropic, epiphytic group remains ambiguous. Microsorum and Polypodium, as traditionally defined, were recovered as polyphyletic. The relatively short branch lengths of the deepest clades contrast with the long branch lengths leading to the terminal groups. This suggests that the polygrammoid ferns arose through an old, rapid radiation. Our analysis also reveals that the rate of substitution in the grammitids is remarkably higher relative to other polygrammoids. Disparities in substitution rate may be correlated with one or more features characterizing grammitids, including species richness, chlorophyllous spores, and an extended gametophytic phase. (C) 2003 Elsevier Inc. All rights reserved
Gymnogrammitis dareiformis is a polygrammoid fern (Polypodiaceae) - Resolving an apparent conflict between morphological and molecular data
No full textMaximum parsimony and maximum likelihood analyses of the combined data sets of two chloroplast genes, rbcL and rps4, demonstrate that the monotypic genus Gymnogrammitis is part of the polygrammoid clade (Polypodiaceae + Grammitidaceae), and not the Davalliaceae as proposed in most studies. The genus forms a clade together with two Asiatic genera of the Polypodiaceae, Arthromeris and Selliguea. These last two genera have either simple or once-pinnate leaves, whereas Gymnogrammitis has highly divided (3- to 4-pinnate) blades. Two characters of this genus, the basic chromosome number of x = 36 and the absence of indusia, support a relationship with the Polypodiaceae. Neither feature is found within Davalliaceae. Three morphological characters support the placement of Gymnogrammitis within the selligueoid lineage of Polypodiaceae: spores with a thick perine extending in microspines, sclerenchymatous strands in the rhizome, and non-clathrate rhizome scales. These results demonstrate that molecular and morphological data are phylogenetically congruent with the exception of blade dissection. Our study clearly shows the pitfalls of classifications based on single characters, and illustrates the importance of phylogenetic assessment of all taxonomic conclusions
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Letter from R. R. Zellick, Assistant Trust Officer, Anglo California National Bank of San Francisco, to Joseph R. Goodman, October 2, 1942
No full textLetter from R. R. Zellick, Assistant Trust Officer at The Anglo California National Bank of San Francisco, to Joseph R. Goodman, regarding property owned by Dave Tatsuno. Zellick mentions a dispute between current tenants and Tatsuno, and that Tatsuno has asked Goodman to help locate trustworthy tenants.Personal correspondence, organizational records, government documents, publications, and other papers created or collected by Joseph R. Goodman documenting the forced removal and incarceration of Japanese Americans during World War II, as well as organized resistance to incarceration. Included in the collection are records of the Japanese Young Men's Christian Association and the Japanese American Citizens' League in San Francisco, including papers of the Japanese YMCA's executive secretary Lincoln Kanai; Sakai family papers; Goodman's correspondence to and from Japanese American incarcerees, organizations opposing forced removal and incarceration of Japanese Americans, the War Relocation Authority, and others; publications, photographs, and ephemera from the Topaz Relocation Center, where Goodman taught high school; War Relocation Authority records and publications; and newspaper clippings, pamphlets, and reports about forced removal and incarceration created by various government, religious, and civic organizations, in California and nationwide
Phylogeny and Evolution of Ferns (monilophytes) With a Focus on the Earlu Leptosporangiate Divergences
No full textThe phylogenetic structure of ferns (= monilophytes) is explored here, with a special focus on the early divergences among leptosporangiate lineages. Despite considerable progress in our understanding of fern relationships, a rigorous and comprehensive analysis of the early leptosporangiate divergences was lacking. Therefore, a data set was designed here to include critical taxa that were not included in earlier studies. More than 5000 bp from the plastid (rbcL, atpB, rps4) and the nuclear (18S rDNA) genomes were sequenced for 62 taxa. Phylogenetic analyses of these data (1) confirm that Osmundaceae are sister to the rest of the leptosporangiates, (2) resolve a diverse set of ferns formerly thought to be a subsequent grade as possibly monophyletic (((Dipteridaceae, Matoniaceae), Gleicheniaceae), Hymenophyllaceae), and (3) place schizaeoid ferns as sister to a large clade of “core leptosporangiates” that includes heterosporous ferns, tree ferns, and polypods. Divergence time estimates for ferns are reported from penalized likelihood analyses of our molecular data, with constraints from a reassessment of the fossil record
Phylogenetic Relationships of the Enigmatic Malesian Fern Thylacopteris (Polypodiaceae, Polypodiidae)
No full textThylacopteris is the sister to a diverse clade of polygrammoid ferns that occurs mainly in Southeast Asia and Malesia. The phylogenetic relationships are inferred from DNA sequences of three chloroplast genome regions (rbcL, rps4, rps4‐trnS IGS) for 62 taxa and a fourth cpDNA sequence (trnL‐trnF IGS) for 35 taxa. The results refute previously proposed close relationships to Polypodium s.s. but support suggested relationships to the Southeast Asiatic genus Goniophlebium. In all phylogenetic reconstructions based on more than one cpDNA region, we recovered Thylacopteris as sister to a clade in which Goniophlebium is in turn sister to several lineages, including the genera Lecanopteris, Lepisorus, Microsorum, and their relatives. Goniophlebium and allies comprise a significant component of vascular fern epiphytes in the rain forests of Southeast Asia and Malesia. The relationships of the genus Thylacopteris as at the base of the clade comprising the genera Goniophlebium, Lecanopteris, Lepisorus, Microsorum, and their relatives indicate that this entire lineage arose in Malesia and subsequently dispersed to continental Asia, Australia, the Pacific, and Africa
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