Showing papers in "Taxon in 2000"

Cytology and cytogenetics as a fundamental taxonomic resource for the 20th and 21st centuries.

Abstract: The status of cytological and cytogenetic data as evidence of value in taxonomic decisionmaking and biosystematic investigations over the past 50 years is surveyed. The main headings considered are chromosome number, genome size, chromosome morphology, chromosome staining characteristics, chromosome and genome disposition in the cell, and chromosome behaviour and homology. The main conclusions are that many of the exciting new developments at the borders of cytogenetics and molecular biology (molecular cytogenetics) are producing a wealth of new data of enormous taxonomic and evolutionary importance, but that for these to reach their full impact it is essential that they are fully integrated with traditional cytological data, the need for which remains as great as ever.

An improved method of DNA isolation from plants collected in the field and conserved in saturated NaCl/CTAB solution.

Abstract: A simple method for isolation of genomic DNA from wild plants sampled in remote field areas is presented. The protocol combines NaCI/CTAB leaf preservation with sorbitol extraction of secondary compounds which often contain inhibitors of Taq DNA polymerase activity. The obtained DNA is suitable for random amplified polymorphic DNA (RAPD) analysis of plant populations as well as for specific amplification of chloroplast DNA sequences. The NaCI/CTAB leaf preservation is a powerful alternative to silica gel dryingbased preservation.

Science in the twentieth century

Abstract: With over forty chapters, written by leading scholars, this comprehensive volume represents the best work in America, Europe, and Asia. Geographical diversity of the authors is reflected in the different perspectives devoted to the subject, and all major disciplinary developments are covered.There are also sections concerning the countries that have made the most significant contributions, the relationship between science and industry, the importance of instrumentation, and the cultural influence of scientific modes of thought. Students and professionals will come to appreciate how, and why, science has developed - as with any other human activity, it is subject to the dynamics of society and politics.

Higher-level classification in the angiosperms: new insights from the perspective of DNA sequence data

Abstract: Higher-level classification of the angiosperms has recently been addressed with large amounts of DNA sequence data, and this wealth of information now facilitates a wide range of other studies as well. An overview is presented of how both the branching pattern and amount of divergence, both morphological and molecular, can be applied to familial and ordinal classification. Angiosperm families have been classified as easily with DNA sequence data as they had been previously with morphological characteristics and represent evolutionary units held together by aspects of genomic organisation developed over long periods of time. Radiations that produced extant lineages (families) only became successful (as measured by taxon-richness) after more of the genomes of these plants were recruited into highly canalised syndromes of characteristics. Thus, single evolutionary novelties are less important in the context of the long histories of these families than is otherwise generally held for recent species/generic radiations. After monophyly, the secondary principles of maximising both information content and support led to the incorporation of divergence into classification. Using DNA patterns as a general meter of overall genetic divergence provides another means of evaluating family delimitation in groups that are not apparently as morphologically cohesive as most, although circumscribing families based on such patterns will inevitably lead to taxa that cannot be readily identified in the field. Nonetheless, in the interests of providing other researchers with a multi-purpose classification, the delimitation of some highly heterogeneous taxa is inevitable.

The Prometheus Taxonomic Model: a practical approach to representing multiple classifications.

Abstract: A model for representing taxonomic data in a flexible and dynamic system capable of handling and comparing multiple simultaneous classifications is presented. The Prometheus Taxonomic Model takes as its basis the idea that a taxon can be circumscribed by the specimens or taxa of a lower rank which are said to belong to it. In this model alternative taxon concepts are therefore represented in terms of differing circumscriptions. This provides a more objective way of expressing taxonomic concepts than purely descriptive circumscriptions have been published. Using specimens as the fundamental elements of taxon circumscription also allows for the automatic naming of taxa based upon the distribution and priority of types within each circumscription, and by application of the International Code of Botanical Nomenclature. This approach effectively separates the process of naming taxa (nomenclature) from that of classification, and therefore enables the system to store multiple classifications. The derivation of the model, how it compares with other models, and the implications for the construction of global data sets and taxonomic working practice are discussed.

Systematic plant morphology and anatomy-50 years of progress

Abstract: Fifty years of comparative and systematic plant morphology and anatomy are reviewed. Thanks to new techniques (TEM, SEM, cinematography, molecular analyses), and new methods and concepts (cladistics, evolutionary paleobotany, molecular systematics and molecular developmental genetics), plant systematics and comparative structural studies saw major progress. The integration of micromorphological with molecular data has led to an increasingly robust phylogeny of the angiosperms. Successes and failures in the premolecular era of phylogenetic classification using morphological and/or anatomical markers only are illustrated with examples. With the new phylogenetic framework, it becomes possible to trace the evolution of characters more accurately than before. Central problems in comparative and systematic structural studies are the meaning of homology and character definition; some aspects have been elucidated but new ones have appeared with the molecular dimension in evolutionary biology. In vegetative anatomy, the integration of ecological and systematic anatomy into "ecophyletic" anatomy has led to a better understanding of the driving forces behind evolutionary diversification of wood and leaf anatomical attributes. However, the intertwining of ecological (extrinsic) and organisational (intrinsic) constraints in the origin of form remains a major challenge for future studies.

Potential plant distribution mapping based on climatic similarity

Abstract: A GIS application of the program ArcView 3.1 is presented that creates potential plant distribution maps based on data from georeferenced specimen data bases. The application makes use of the relationship between species distribution and environmental parameters such as altitude, humidity, or temperature, to predict a taxon's potential distribution. The application contains tools for modification and further refinement of basic maps.

Deep phylogenetic relationships among "plants" and their implications for classification

Abstract: There has been tremendous recent progress in understanding the relationships of plants, due to two different advances, whose cumulative impact has been great. One advance is theoretical and methodological-a revolution in how any sort of data can be used to reconstruct phylogenies. The other is empirical-the sudden availability of copious new data from the DNA level. This review briefly sets these advances in their historical context, then covers both as to their promise and problems. An important distinction between "shallow" and "deep" phylogenetic studies is developed, and morphological and molecular data are compared as potential phylogenetic markers in that context. Recent results on relationships of plants in general and green plants in particular are then considered. Future directions for classification, particularly the need for rank-free taxonomy, are also discussed in light of the rapidly improving resolution of plant relationships.

A molecular phylogeny of Tropaeolaceae and its systematic implications

Abstract: Trophaeastrum should be reduced to synonyms of Tropaeolum. The two new combinations Tropaeolum porifolium (Cav.) L.Andersson & S.Andersson and T. trialatum (Suess.) L.Andersson & S.Andersson are made. Further, although most of the sections of Tropaeolum that were recognised in Sparre and Andersson's monograph are monophyletic, only two entities can be distinguished that are both monophyletic and morphologically diagnosable. Therefore, the genus Tropaeolum should be subdivided into two sections, T. sect. Tropaeolum and T. sect. Chilensia. Tropaeolum sect. Tropaeolum should include the formerly recognised sections Bicolora, Dipetala, Mucoronata, Schizotrophaeum, Serratociliata, Tropaeolum, and Umbellata. Tropaeolum sect. Chilensia should include the formerly recognised genera Magallana and Trophaeastrum, and the formerly recognised T. sect. Chymocarpus.

Maesaceae, a new primuloid family in the order Ericales s.l.

Abstract: Evidence from morphology and molecular sequence data from three chloroplast genes, rbcL, ndhF, and atpB, have shown that the genus Maesa constitutes an evolutionary lineage separate from the other ...

The Cerastium alpinum-C. arcticum complex (Caryophyllaceae): numerical analyses of morphological variation and a taxonomic revision of C. arcticum Lange s.l.

Abstract: Morphological variation of Cerastium alpinum L., C. arcticum Lange, and related taxa was investigated by numerical analyses. The analyses showed that the present division into two species is inappropriate and does not cover the levels of variation within the C. alpinum-C. arcticum complex. Two alternative models for a new and functional taxonomy of the complex are discussed: (1) that there is one widely defined species, C. alpinum, including several subspecies, (2) alternatively that arctic and non-arctic populations of what currently is named C. arcticum belong to two different taxa, both distinct from C. alpinum. Our studies indicate the presence of several evolutionary lineages, which are not adequately accounted for by the recognition of a widely circumscribed C. alpinum, and support a subdivision of current C arcticum into two separate species, C. arcticum Lange s.str. and C nigrescens (H.C. Watson) Edmondston ex H.C. Watson. A revised taxonomic treatment is presented.

Viburnales: cytological features and a new circumscription

Abstract: Summary Cornaceae, and Hydrangeaceae point to a very close relationship between the Viburnaceae, Sambucaceae and Adoxaceae, corroborating the inclusion of these families into an order different from the Dipsacales, namely the Viburnales. Many cytological features shared by these families differ strongly from the Dipsacales s.str., especially (1) chromosome size and morphology, (2) the presence of cold induced chromosome regions (CIRs), (3) interphase nuclear structure, and (4) chromosome condensing behaviour at prophase. Cornaceae and Hydrangeaceae present similar interphase nuclei, but differ from the Viburnales by other karyomorphological characters. The results are discussed with respect to previous morphological, embryological, and molecular findings.

Taxonomy of Cardamine amara (Cruciferae) in the Iberian Peninsula

Abstract: Summary Lihova, J., Marhold, K. & Neuffer, B.: Taxonomy of Cardamine amara (Cruciferae) in the Iberian Peninsula. – Taxon 49: 747–763. 2000. – ISSN 0040-0262. Cardamine amara is represented in the Iberian Peninsula by two subspecies: the diploid (2n = 16) subsp. pyrenaea, occurring in the Eastern Pyrenees, and the tetraploid (2n = 32) subsp. olotensis, concentrated at the lower altitudes in Catalonia, N and NE of Barcelona. Morphometric analysis of populations of these taxa and four other subspecies of C. amara, which occur in other parts of Europe, supported their subspecific distinctness. RAPD (Random Amplified Polymorphic DNA) analysis of a ll six European subspecies of C. amara provided more evidence supporting this taxonomic treatment. Lectotypes were designated for the following names: C. amara var. parviflora Cadevall, C. amara subsp. pyrenaea Sennen, C. amara subsp. siifolia Sennen, and C. amporitana Sennen & Pau.

Pontechium: a new genus distinct from Echium and Lobostemon (Boraginaceae)

Abstract: The phylogenetic relationships of Echium, Lobostemon, and Echiostachys (BoraginaceaeLithospermeae) were inferred from DNA sequence variation. The presence of a bicapitate rather than a bifid stigma and plastid trnMuAA) intron, trnl(uAA)-trnF(GAA) spacer and nuclear (ITS 1) DNA sequence analyses confirm an isolated position for Echium maculatum L. and recommend exclusion from the genus Echium (Boraginaceae) as a new genus: Pontechium.

Vestured pits in Malvales s.l.: a character with taxonomic significance hidden in the secondary xylem

Abstract: The distribution of vestured pits in the secondary xylem of all major groups of Malvales s.l. is investigated and compared with recent circumscriptions and phylogenetic insights of the order. While the monophyly of the core Malvales, including Bombacaceae, Malvaceae s.str., Sterculiaceae, and Tiliaceae, is supported by the lack of vestured pits, the character is consistently present in three malvalean alliances that are well supported based on molecular data: (1) Bixaceae, Cochlospermaceae, and Diegodendraceae; (2) Cistaceae, Dipterocarpaceae s.l. (including Monotaceae), and Sarcolaenaceae; and (3) Thymelaeaceae s.l. (including Aquilariaceae and Gonystylaceae). Vestured pits are absent in other malvalean taxa such as Petenaea, Muntingiaceae, Neuradaceae, and Sphaerosepalaceae. Families that are now excluded from the order, such as Dirachmaceae, Elaeocarpaceae, and Huaceae also have non-vestured pits. Rudimentary vestures in Plagiopteraceae, however, do not necessarily indicate a malvalean affinity.

Naming the groups: developing a stable and efficient nomenclature

Abstract: The binomial system of botanical nomenclature has existed for almost 250 years, the principle of a taxon having a single correct name determined on the basis of priority of publication was formalized almost 150 years ago, and the type method for the application of scientific names of plants has had international acceptance for almost 75 years. In this historic time-frame, the achievements of the past 50 years are outlined and the question posed as to whether the next 50 years hold any prospect of change, and indeed whether any change is possible or even desirable. The requirement of botanical nomenclature to provide a stable, unambiguous reference system for plant information implies an inherent conservatism of rules and procedures--even the smallest change to the Code, however beneficial it may be in general, is virtually certain to have some destabilizing effect. Despite this truism, it is suggested that the next few years will see quite major change. One of the least of these may be the development of a separate specialist nomenclature for communication about major phyletic lineages, not so dissimilar in practice from the specialist nomenclature currently in existence for the micro-variants important in cultivated plants. Bionomenclature provides the mechanism for communication about the elements of taxonomy-elements that generally seek to reflect the greatest information on patterns of biodiversity. It will continue to communicate the general information content of taxa effectively, only if it evolves to take fuller advantage of the opportunities of the electronic age. The historical tendency to improve the rules of nomenclature by continuous "tinkering" with the Code needs to give way to a recognition that stability and simplicity are key requirements of users of names (amongst whom professional biologists are a relatively small minority), and that web access to authoritative lists will generally be their preferred approach to answering the nomenclatural questions that arise in study and use of plants, animals and micro-organisms. To remain relevant, the botanical Code, like the bacteriological, and now, to a degree, the zoological, must provide mechanisms for the endorsement of nomenclatural lists that represent the products of sound scholarship.

The Definitions of Taxon Names: A Reply to Stuessy

Abstract: Phylogenetic nomenclature (e.g., de Queiroz & Gauthier, 1990, 1992, 1994; Cantino & de Queiroz, 2000) is an alternative to the traditional system of nomenclature described in the bacteriological, botanical, and zoological codes (e.g., Sneath, 1992; Ride & al., 1999; Greuter & al., 2000). The most fundamental difference between phylogenetic and traditional nomenclature concerns the manner in which taxon names are defined (de Queiroz & Gauthier, 1994; de Queiroz, 1997). Stuessy (2000), however, has questioned whether taxon names are defined at all. In his view, the three types of phylogenetic definitions that have been describednode-based, stem-based, and apomorphy-based (not crown-based, contra Stuessy)are not definitions of names but methods or concepts for taxon circumscription that have nothing to do with nomenclature (i.e., names). Stuessy's view is incorrect; it misrepresents the function of phylogenetic definitions and fails to account for how existing taxon names are applied in new taxonomic contexts under both traditional and phylogenetic systems. Stuessy did not present any evidence to support his conclusion that phylogenetic definitions are methods for taxon circumscription rather than definitions; he simply asserted his conclusion and described his view of how taxa are named under the traditional system. According to Stuessy (p. 23), "...taxa are first circumscribed (or delimited or recognised) by some stated criteria. Taxa are then referred to categories of the moder taxonomic hierarchy. .... Through the process of referral of a taxon to a category, it receives a name by 'christening' or 'baptism'. These names are given in the fashion we name our own children, John Smith or Jane Jones; they are not defined-they are just labels to allow for effective communication". Except for the statement that taxon names are not defined, this is a more or less accurate description of how the traditional system operates. The phylogenetic system operates similarly in some respects and differently in others. One important difference is that in the phylogenetic approach, taxa need not be referred to categories in a taxonomic hierarchy; consequently, they do not receive their names through categorical referral. Contrary to Stuessy's view, taxon names are defined in both traditional and phylogenetic systems of nomenclature (de Queiroz, 1997). In the traditional system of nomenclature, taxon names are defined in terms of types and taxonomic categories. For example, the definition of the name Asteraceae is "the taxon containing the genus Aster that is assigned to the family category". In the phylogenetic system, taxon names are defined in terms of specifiers and their common ancestry relationships. For example, a node-based phylogenetic definition of the name Asteraceae might be "the clade stemming from the most recent common ancestor of Bamadesia and Aster". Perhaps the reason Stuessy thinks that taxon names are not defined is that definitions under the traditional system are taken for