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Several indices that measure the degree of balance of a rooted phylogenetic tree have been proposed so far in the literature. In this work we define and study a new index of this kind, which we call the total cophenetic index: the sum, over all pairs of different leaves, of the depth of their lowest common ancestor. This index makes sense for arbitrary trees, can be computed in linear time and it has a larger range of values and a greater resolution power than other indices like Colless’ or Sackin’s. We compute its maximum and minimum values for arbitrary and binary trees, as well as exact formulas for its expected value for binary trees under the Yule and the uniform models of evolution. As a byproduct of this study, we obtain an exact formula for the expected value of the Sackin index under the uniform model, a result that seems to be new in the literature.  相似文献   

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Crepidotus ehrendorferi spec. nova (sect.Sphaerula) is similar to the North AmericanC. sinuosus and differs mainly by the anatomy of pileicutis with unseptated, long, slender terminal hyphae and some macroscopical characters. It is compared also withC. applanatus andC. crocophyllus. C. ehrendorferi is a very conspicuous, wood-inhabiting species known up to now from a very old forest reserve close to the city of Vienna (Austria).  相似文献   

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Psilocybe laetissima sp. n. of the sect.Merdariae is close toP. sabulosa s.l. and known to us from Austria, Hungary, and West Germany.  相似文献   

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The European Water Framework Directive (WFD) (2000/60/EC) requires assessing the ecological quality status of water bodies, and gives great importance to the biological components of the ecosystem. Within this framework, a multimetric, fuzzy-based index for the evaluation of environmental quality (FINE: fuzzy index of ecosystem integrity) has been developed using data from several Italian coastal lagoons, gathered with seasonal frequency at diverse sites in each lagoon. The rationale of FINE is that certain attributes, selected on the basis of established principles of benthic ecology, are fundamental for lagoon ecosystem function. FINE is composed of seven ecosystem attributes (variables) each of which have ecological relevance for lagoon ecosystems. Individually, all these attributes are themselves useful indices of environmental conditions. However, the combination of these attributes into a single fuzzy index, provides a more robust, overall index of the response of the natural communities to environmental perturbations and avoids misleading or ambiguous results. Each variable is not represented by a single numerical value, but by several categories that describe its properties: in the present model we considered a total of seven variables: two with four modalities (low–medium–high–very high), one with three (low–medium–high) and three with two (low–high), plus a qualitative variable (yes–no), that altogether generate 768 rules. FINE is a low-cost, flexible and robust routine index of lagoon ecosystem impairment and could be of particular benefit to environmental managers and policymakers who require tools capable of expressing the degree of degradation or environmental quality of different lagoon habitats. For its relative simplicity in the application, FINE could be a good candidate to assess the environmental quality of Mediterranean transitional ecosystems. Guest editors: A. Razinkovas, Z. R. Gasiūnaitė, J. M. Zaldivar & P. Viaroli European Lagoons and their Watersheds: Function and Biodiversity  相似文献   

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The poly(A) segment increases in length as the complexity of the organism increases. The shortest poly(A) size (10–15 AMP units) exist on mRNA from bacteria. The largest poly(A) segments (180–200 AMP units) exist in highly differentiated tissue. The natural log of average poly(A) size has evolved in a linear manner with the time of evolution of different organisms. This relationship places the origin of mRNA, and possibly life, at 3·85 ± 0.2 billion years ago. The poly(A) length of mitochondrial mRNA places the origin of mitochondria within eucaryotes at 2· 1 billion years ago.  相似文献   

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George M. Diggs 《Brittonia》1986,38(4):344-351
Comarostaphylis spinulosa subsp.glandulifera is described from the mountains of Oaxaca and Puebla, Mexico. Four new combinations inComarostaphylis are also made:C. arbutoides subsp.costaricensis, C. discolor subsp.rupestris, C. polifolia subsp.minor, andC. spinulosa.Arctostaphylos glabrata, A. rupestris, andA. spinulosa are lectotypified and the status ofC. polifolia is discussed.  相似文献   

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Hibiseadelphus distans is described. The validity of the generic concept is considered, a key to the species is provided, and the status of each species is discussed.  相似文献   

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Senecio ganderi is described as new from San Diego County, California. It is referable to theAurei species-group and is distinguished by its orange-yellow corollas, cordate to subcordate basal leaves, and its restriction to chaparral and recently burned areas.  相似文献   

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A new tree species from Colombia, closely resembling other members of the neotropical genusCatostemma in its large one-seeded fruits, is described and illustrated.Catostemma digitata has palmately compound leaves, previously unknown in mature individuals of this genus.  相似文献   

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A rare variant of Factor B exhibiting a mobility intermediate between BF F and BF S was described. After comparison with the mobilities of BF F and F075, this variant was designated BF F025. The allele was transmitted together with C2*C, C4A*3, and C4B*1.  相似文献   

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John G. Stutts 《Brittonia》1983,35(4):351-352
Vernonia rigiophylla Schultz-Bip. ex Baker is a later homonym ofV. rigiophylla DC. and therefore a new name,Vernonia elsieae, is proposed for this species.  相似文献   

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Allium stoloniferum, a new species from southern Mexico, belongs to theA. kunthii alliance on the basis of the appearance of the perianth segments and the presence of long slender rhizomes, but differs by the presence of bulbils.  相似文献   

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Distinctly mucronate anther cells and the 4-seeded capsule ofHygrophila pringlei Greenman together with several other additional characters, suggest that this taxon would be better treated asDyschoriste rubiginosa, nom. nov.  相似文献   

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Joosia comprises 11 species, three of which are here described as new: J. longisepala, J. multiflora, and J. obtusa. Joosia pulcherrima Steere is resurrected from synonymy. Joosia is a close relative of Cinchona, Ladenbergia, and Remijia, from all of which it differs in having wilting rather than caducous stipules, an inflorescence of predominantly monochasial cymes, and corolla lobes with marginal showy appendages. It occurs from western Panama along the Andes south to northern Bolivia, with a pronounced center of diversity in Ecuador. On the basis of a cladistic and biogeographical analysis, it is hypothesized that the genus originated in the lowland forest of the westernmost Amazon Basin.  相似文献   

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