Showing papers in "Taxon in 2001"
TL;DR: The recent paper by Rafael Govaerts in Taxon 's Points of View and his omission of my counts in my recent Botanical Review paper (Thorne, 2000a) inspired me to recount (several times) the figures in my latest update of my classification of the angiosperms.
Abstract: The recent paper by Rafael Govaerts (2001) in Taxon 's Points of View and his omission of my counts in my recent Botanical Review paper (Thorne, 2000a) inspired me to recount (several times) the figures in my latest update of my classification of the angiosperms. I am amazed at the complicated ways Govaerts has used to estimate the number of species of seed plants. It seems to me much simpler just to add up all the figures from recent monographs and revisions, supplemented by figures from Mabberley's The Plant Book (1997) when recent revisions are not available. Govaerts estimates about 400,000 published accepted species of seed plants. My latest count of accepted species of angiosperms is about 258,650 in 13,553 accepted genera (see website http://www.inform.umd. edu/PBIO/fam/thomeangiosp99.html). One would have to add to that the other seed plants for an estimate of 260,000 accepted species. Probably if all the undescribed species of seed plants of the world were added, the total number of species of seed plants might approximate Govaerts' estimate of published accepted species. For the statistically inclined, my latest count (as of March 21, 2002; Table 1) of angiosperm taxa now accepted by me is 258,650 species in 13,553 genera, 490 families and 388 subfamilies (for a total of 768 subfamilies and undivided families), 82 orders (and 53 suborders), 30 superorders and 10 subclasses. Monocot totals
348 citations
TL;DR: Although the text is dense and detailed, helpful listings in the side margins of each page are included so that at a quick glance the reader can see a drawing of the plant, a map of its distribution, a listing of the problematic species, an indication of what plant parts are involved, a summary of the symptoms, and a list of the toxic compounds.
Abstract: NATIVEPLANTS | FALL 2003 his huge book (22 x 28 cm [8.5 x 11 in]; 1342 pages) is an encyclopedic account of the poisonous plants of North America. The book begins with a brief introduction describing the objectives, scope, organization, and format of the text. Families of vascular plants are then listed alphabetically, with ferns, gymnosperms, monocots, and dicots all grouped into a single alphabetical list. Included for each family is a family description with notes on the natural history and uses of the plants. The genera that include poisonous species are then listed alphabetically, and each generic account includes a description of the genus, a list of toxic species, distribution and habitat, disease problems, disease genesis, clinical signs, pathology, and treatment. Each family account then concludes with an extensive bibliography. Both native species and commonly used ornamentals are included, and the toxic effects of these plants on animals and humans are extensively described and referenced. Also included are many notes on medicinal uses of the species. Although the text is dense and detailed, helpful listings in the side margins of each page are included so that at a quick glance the reader can see a drawing of the plant, a map of its distribution, a listing of the problematic species, an indication of what plant parts are involved, a summary of the symptoms, and a list of the toxic compounds. A total of 76 families are described in detail, beginning with the Aceraceae and concluding with the Zygophyllaceae. Toxic Plants of North America
224 citations
164 citations
TL;DR: It is concluded that species are the most inclusive entities that directly participate in evolutionary processes, and the traditional role of gene flow as a force that constrains differentiation due to genetic drift or local adaptation has been over-emphasised relative to its creative role as a mechanism for the spread of advantageous mutations.
Abstract: substantially different than higher taxa. This claim is based on reports that (1) levels of intraspecific gene flow may be too low to account for species' integration, and (2) populations are likely to diverge rather than evolve in parallel when exposed to uniform selection pressures. These conclusions are premature. A review of the plant literature reveals that there is sufficient gene flow to enable the efficient spread of strongly favourable alleles (s > 0.05), the most likely agents of collective evolution. Moreover, estimates of s for major quantitative trait loci (QTLs) are sufficiently large to enable their spread across the range of a species, although minor QTLs seem more likely to evolve locally. In addition, evidence that intraspecific variation in genetic background affects the response of alleles to selection is rare, but examples of parallel genotypic evolution are becoming increasingly common. We conclude that, as traditionally believed, species are the most inclusive entities that directly participate in evolutionary processes. However, we also note that the traditional role of gene flow as a force that constrains differentiation due to genetic drift or local adaptation has been over-emphasised relative to its creative role as a mechanism for the spread of advantageous mutations.
162 citations
134 citations
TL;DR: Studies of 31 new sequences of species belonging to 30 genera in the Parmeliaceae family demonstrate that the mitochondrial DNA (mtDNA) SSU region has the potential to play a major role in establishing the phylogeny and stabilising generic concepts in some of the world's most conspicuous lichens.
Abstract: A satisfactory resolution of the current instability of generic concepts in the parmelioid lichens, and particularly Parmelia s.l., has not so far emerged from molecular studies. The rDNA ITS sequence has proven too variable and the rDNA SSU too conserved to provide satisfactory discrimination around the family and generic levels in Parmeliaceae s.l. Studies of 31 new sequences of species belonging to 30 genera in the family (including the type species of 21) are reported here. These demonstrate that the mitochondrial DNA (mtDNA) SSU region has the potential to play a major role in establishing the phylogeny and stabilising generic concepts in some of the world's most conspicuous lichens. Some clades identified appear to correlate with differences in cell wall carbohydrates, epicortical, conidial, and other features. The emerging groupings now need to be further tested by the inclusion of sequences from additional genera and species. Nomenclatural changes should not be made until further work has been carried out.
96 citations
TL;DR: A historical biogeographic analysis of Nothofagus is reported where the reconciled trees between a well-supported Noth ofagus phylogeny and two geological hypotheses are compared: the current view of Gondwana break-up, and the areagram by Linder & Crisp.
Abstract: The Austral biota reveals many links between Australasia and South America that have challenged biogeographers for many years. Nothofagus, the Southern Beech, is probably the classical example. With the general acceptanceof continental drift, the break-up of Gondwana is regarded as primarily responsible for many disjunct patterns expressed in the Southern Hemisphere biota. Vicariance biogeography is the principal tool used to investigate biogeographic patterns of extant plant groups, resulting in areagrams or general area cladograms. These are often at odds with current geological knowledge, and on this basis, alternative hypotheses of area relationships and geological history have, therefore, been suggested. One such areagram was recently advocated by Linder & Crisp (1995) in a biogeographic analysis of Nothofagus. Three explanations, often in combination, account for incongruence: long-distance dispersals, extinctions, and erroneous geological models. All of these parameters ought to be considered in the analysis. Here we report the result of a historical biogeographic analysis of Nothofagus where we compare the reconciled trees between a well-supported Nothofagus phylogeny and two geological hypotheses: (1) the current view of Gondwana break-up, and (2) the areagram by Linder & Crisp. Our analysis makes use of extant and extinct taxa, as well as the assumption of long-distance dispersals as defined by maximized vicariance. Our results show that Nothofagus existed prior to the break-up of Gondwana and, most importantly, its present distribution supports, and is dependent upon, the traditional break-up sequence of East Gondwana, compatible with three vicariance events. The areagram, conceived as an alternative geological hypothesis, presents a more parsimonious solution, but fails to explain numerous past distributions in areas such as Antarctica, South America, and Tasmania. We therefore recommend a conservative approach to use (general) areagrams in historical biogeography.
90 citations
77 citations
TL;DR: Phylogenetic relationships within the genus Helleborus (Ranunculaceae) were evaluated with analyses of plastid trnL-F and partial matK and nuclear ITS DNA sequences for all 16 currently recognised species in addition to several subspecies and geographical variants, providing strong support for the monophyly of the genus.
Abstract: Phylogenetic relationships within the genus Helleborus (Ranunculaceae) were evaluated with analyses of plastid trnL-F and partial matK and nuclear ITS DNA sequences for all 16 currently recognised species in addition to several subspecies and geographical variants. The molecular study provides strong support for the monophyly of Helleborus. However, both traditional divisions of the genus, into two groups (Caulescentes and Scapigeri) or two subgenera (Helleborastrum and Helleborus), are refuted. All six currently recognised sections (Dicarpon, Chenopus, Griphopus, Helleborus, Helleborastrum, and Syncarpus) are monophyletic, four by default because they are monospecific. Section Dicarpon (H. thibetanus) is strongly supported as sister group to section Helleborastrum and could therefore be sunk into that section. Relationships between this pair of sections and the other sections are, however, not clear. At the specific level, all species which are clearly distinct morphologically are also distinct in terms of molecular divergence, but relationships between the poorly differentiated species in section Helleborastrum are not resolved with any degree of support. Using a molecular clock based on matK sequence divergence, the disjunction of H. thibetanus and section Helleborastrum between East Asia and the Mediterranean is tentatively dated at approximately 23 million years (middle Miocene), which corresponds well with the geological history of the area where H. thibetanus occurs.
77 citations
TL;DR: The results suggest that the genus Anthemis, in its traditional circumscription, is not monophyletic due to the consistent placement of a member of Tripleurospermum amidst the Anthemis representatives.
Abstract: Sequences of the nrDNA internal transcribed spacer (ITS) region were analysed for 29 representatives of Anthemis L. and six outgroup taxa of Anthemideae (Compositae) to study the delimitation and the infrageneric taxonomy of this large and widespread Eurasian and African genus. Species of Anthemis included all subgenera and sections traditionally used in supraspecific classifications of the genus. Maximum parsimony (MP), maximum likelihood (ML), and distance (neighbor joining, NJ) analyses were carried out for phylogenetic reconstructions. The results suggest that the genus, in its traditional circumscription, is not monophyletic due to the consistent placement of a member of Tripleurospermum amidst the Anthemis representatives. Subdivision of Anthemis into two subgenera (A. subg. Anthemis, A. subg. Cota) is supported, with the exception of the placement of A. sect. Chiae and sect. Odontostephanae which fall outside A. subg. Anthemis. Within A. subg. Anthemis, life form dependent delimitation of A. sect. Anthemis (annuals) against A. sect. Hiorthia (perennials) is not supported, whereas the monophyly of other sections (A. sect. Maruta, A. sect. Rascheyanae) is confirmed including the placement of Ammanthus Boiss. & Heldr. into Anthemis subg. Anthemis.
TL;DR: It is demonstrated that vestured pits frequently support results from DNA data, and implies numerous parallel origins in divergent, major taxa.
Abstract: The distribution of vestured pits in secondary xylem reveals interesting patterns that may bear on hypotheses of phylogenetic relationships within eudicots. Vestured pits are found to be relatively widespread at the base of the eurosids I, eurosids II, and euasterids I, but the feature probably has been lost or originated independently in several more derived branches of these clades. Vestured pits characterise orders Myrtales and Gentianales sensu APG; other large monophyletic taxa that consistently show vestured pits include Malpighiaceae, Polygonaceae, Brassicaceae, and most Fabaceae. Representatives from euasterids II always show nonvestured pits. The occurrence of the character implies numerous parallel origins in the following divergent, major taxa: (1) Proteaceae, (2) Polygonaceae (Caryophyllales), (3) eurosids I (Zygophyllaceae, Fabales, very few Rosales, Malpighiales), (4) eurosids II (Myrtales, Malvales, Brassicales), and (5) euasterids I (Gentianales, Lamiales, Solanales). It is demonstrated that vestured pits frequently support results from DNA data.
TL;DR: The last fifty years have been a time of accelerated plant collection, especially in the tropics, and this is a race against time since the destruction of natural habitats has also increased dramatically as mentioned in this paper.
Abstract: The last fifty years have been a time of accelerated plant collection, especially in the tropics. However, this is a race against time since the destruction of natural habitats has also increased dramatically. The rate at which collecting is still adding new species of flowering plants indicates that the inventory is not nearly complete, and that the past estimates of total species numbers are low and should be increased to 320,000. The production of florulas and quantitative inventories of small areas of the tropics, accompanied by intensive fieldwork, has greatly helped to improve the level of inventory. Future collecting should be carefully targeted towards areas that are particularly threatened, such as those defined as hotspots, and also collection of rare species rather than repeated over-collection of widely distributed common taxa. Future collecting should also gather material for ancillary studies such as molecular work and evolutionary development.
TL;DR: The island species of Phylica formed a monophyletic group together with the widespread mainland species, P. paniculata, and occupies a derived position in the phylogenetic trees, thus indicating either a reversal or more likely the retention of these primitive traits.
Abstract: Las relaciones de las especies insulares de Phylica y otros generos en Phyliceae ( Rhamnaceae ) se evaluaron utilizando secuencias para el intron trnL del plastidio , el espaciador intergenico trnL-F y los espaciadores transcritos internos del ADN ribosomico nuclear. Ambas regiones proporcionaron patrones filogeneticos casi identicos, por lo que se analizaron como una matriz combinada. Se encontro que los generos Nesiota y Noltea eran especies paleoendemicas dentro del contexto de la tribu. La especie islena de Phylica formo un grupo monofiletico junto con la especie extensa del continente, P. paniculata.La morfologia plesiomorfica y generalista de este grupo contrasta con las caracteristicas morfologicas derivadas de la mayoria de las especies continentales. Sin embargo, el grupo ocupa una posicion derivada en los arboles filogeneticos, lo que indica una inversion o, mas probablemente, la retencion de estos rasgos primitivos.
TL;DR: The distribution and diagnostic characters of Nassella are presented and several new distribution records are documented, making it one of the largest genera in tribe Stipeae.
Abstract: Barkworth, M. E. & Torres, M. A.: Distribution and diagnostic characters of Nassella (Poaceae: Stipeae). Taxon 50: 439-468. 2001. ISSN 0040-0262. Nassella sensu lato includes 116 species, making it one of the largest genera in tribe Stipeae. Argentina has the largest number of species, 72, with the greatest concentration being in the northwestern part of the country. Bolivia, Chile, and Uruguay have 26, 27, and 27 species, respectively. Other South American countries in which the genus is present are Brazil (18 species), Colombia (8), Ecuador (9), Paraguay (4), Peru (18), and Venezuela (2). Guatemala has two species, but Costa Rica only one. Mexico has eight native species, five of which also grow in the United States. One additional species grows in both the United States and Canada. Sixty species are known only from one country; one species, N. mexicana, grows in eight countries. Several new distribution records are documented: N. caespitosa, N. elata, N. leptothera and N. punensis for Bolivia, N. pauciciliata and N. spegazzinii for Brazil, N. airoides, N. argentinensis, N. spegazzinii for Paraguay, and N. tucumana (= N. asperifolia) for Peru. Three new combinations are presented: N. burkartii, N. ligularis, and N. quinqueciliata. Two recently transferred species, N. barrancaensis and N. brachychaeta, are excluded from the genus and N. asperifolia, N. bonariensis, and N. amethystina are placed in synonymy. Tables summarising the distribution of Nassella and its morphological variation are presented.
TL;DR: Genealogical analysis coupled with the theoretical framework of coalescence theory can be used to estimate the roles of migration, founder effects and range expansion during the formation and subsequent establishment of species.
Abstract: Traditionally population genetics and systematics have been separate fields, with distinct conceptual frameworks, tools, and statistics. Hennig drew a clear distinction between the reticulate genealogical relationships among individuals and populations on one hand, and the hierarchical phylogenetic relationships among divergent species or taxa on the other. For many plant species, such distinctions blur. The genetic structuring of plant populations is strongly affected by phylogenetic history, and the phylogenetic relationships among species are frequently confounded by gene migration between species. The identification of molecular markers that vary within species, as well as reductions in costs and time associated with DNA sequencing, have set the stage for a blending of the two fields. Haplotype variation at a non-recombining locus can be historically ordered to produce a gene genealogy. Genealogical analysis coupled with the theoretical framework of coalescence theory can be used to estimate the roles of migration, founder effects and range expansion during the formation and subsequent establishment of species. Such studies hold great promise for understanding the interplay of phylogenetic history and population level process in shaping distinct evolutionary lineages.
TL;DR: The diagnostic characters include: (1) ternately divided compound trophophore; (2) linear and fleshy sporophore branched at base; and (3) creeping rhizome with proliferous roots.
Abstract: Mankyua chejuense gen. & sp. nov. (Ophioglossaceae) is described from a lowland swampy area of Cheju Island off the south coast of the Korean Peninsula. The diagnostic characters include: (1) ternately divided compound trophophore; (2) linear and fleshy sporophore branched at base; and (3) creeping rhizome with proliferous roots. The new fern is somewhat morphologically related to Helminthostachys and Ophioglossum, but distinct enough to merit generic status.
TL;DR: Molecular and morphological evidence suggests that Phyllospadix is the most divergent taxon, while Heterozostera and Nanozostera are the most closely related.
Abstract: The seagrass family Zosteraceae may be divided into four groups of species on the basis of morphological and developmental evidence. It is proposed to treat each of these groups as a genus; this involves the elevation of Zosterella from subgeneric to generic rank as Nanozostera. The family thus now includes: Heterozostera (one sp.), Nanozostera (eight spp.), Phyllospadix (five spp.), and Zostera (four spp.). Molecular and morphological evidence suggests that Phyllospadix is the most divergent taxon, while Heterozostera and Nanozostera are the most closely related.
TL;DR: It is suggested that apomorphy-based phylogenetic definitions of taxon names are preferable to other types of definitions, for both historical reasons (apparent similarity to existing Linnaean definitions, ability to fix "key" innovations to the diagnoses of higher taxa), and practical reasons (being useful in poorly resolved groups).
Abstract: Although systematists agree that the most generally useful taxonomy is one based on phylogenetic relationships, there is continuing debate about what system is most suited for this purpose: the established rank-based system, usually (but perhaps not very appropriately: Stuessy, 2000) termed "Linnaean taxonomy", or a new and explicitly phylogenetic system. A recent paper asserts polemically that Linnaean nomenclature is superior to phylogenetic nomenclature (Nixon & Carpenter, 2000). However, that work misunderstands the nature of both Linnaean and phylogenetic nomenclature. It thus instead ends up arguing almost the exact opposite: that apomorphy-based phylogenetic definitions of taxon names are superior to other types of definitions, including nodeand stem-based phylogenetic definitions and Linnaean definitions. I will here discuss this viewpoint and concur by suggesting that apomorphy-based phylogenetic definitions might be preferable to other types of definitions, for both historical reasons (apparent similarity to existing Linnaean definitions, ability to fix "key" innovations to the diagnoses of higher taxa), and practical reasons (being useful in poorly resolved groups). Nixon & Carpenter (2000: 306) advocate (as "good Linnaean taxonomy") the following procedure for defining taxon names:
TL;DR: Molecular systematics has become the over-arching field in systematics, but each of eight other areas (genome, chromosomes, morphology and anatomy, development, population biology, speciation, floristics and monography, nomenclature and classification) are evaluated.
Abstract: In the historical context of plant systematics over the last 50 years, systematics is examined in terms of where it is now, where it is headed, where it should be, and how it should get there. Issues and concerns of the past decades are still with us today. Molecular systematics has become the over-arching field in systematics, but each of eight other areas (genome, chromosomes, morphology and anatomy, development, population biology, speciation, floristics and monography, nomenclature and classification) are evaluated. A revolution in
TL;DR: The liverwort genus Cyrtolejeunia A.L. Evans is reduced to synonymy under Cheilolejeunea (Spruce) Schiffn.
Abstract: The liverwort genus Cyrtolejeunea A. Evans is reduced to synonymy under Cheilolejeunea (Spruce) Schiffn. because of the existence of a series of intermediate species, including Cheilolejeunea insecta Grolle & Gradst. sp. nov. from Bolivia and Brazil and Cheilolejeunea chenii R.L. Zhu & M.L. So from eastern China. The new combinations, Cheilolejeunea holostipa (Spruce) Grolle & R.L. Zhu comb, nov. and C. suzannensis (Grolle) Grolle & R.L. Zhu comb, nov., are proposed.
TL;DR: It is argued for concerted efforts to reconstruct the green plant clade of the Tree of Life, as well as the rest of theTree, and ways in which the Tree can be used further for inferring and testing hypotheses of evolution are suggested.
Abstract: The Tree of Life represents the fundamental framework for ordering biological information. In this paper, we argue for concerted efforts to reconstruct the green plant clade of the Tree of Life, as well as the rest of the Tree, and suggest ways in which the Tree can be used further for inferring and testing hypotheses of evolution. We suggest characters, from DNA sequences to genomic characters, for use in reconstructing the phylogeny of plants. Challenges in data analysis must also be met, if we are to reconstruct the phylogeny of nearly half a billion species of green plants. Phyloinformatics, the storage, retrieval, and use of phylogenetic data and phylogenetic trees, must play an increasingly important role in plant systematics and the systematics community as a whole. Both functional and comparative genomics will benefit from integration with phylogenetic information, and these fields may provide new characters for phylogeny reconstruction. A synthetic view of plant phylogeny requires the incorporation of fossils; a major challenge facing paleobotanists and plant systematists is the integration of these disciplines. In sum, molecular systematics, through interfaces with many other fields, from genomics to computer science to paleobotany, will long remain an "unending synthesis".
TL;DR: The systematic position of the thistle-like Gundelia of Asteraceae-Arctoteae is investigated by using sequences from the chloroplast gene ndhF in a parsimony jackknife analysis, which indicates strong support for placing Gundelia with tribe Lactuceae, rather than with tribe ArctoteAE.
Abstract: The systematic position of the thistle-like Gundelia of Asteraceae-Arctoteae is investigated by using sequences from the chloroplast gene ndhF in a parsimony jackknife analysis. Unexpectedly, the analysis indicates strong support for placing Gundelia with tribe Lactuceae, rather than with tribe Arctoteae. Gundelia's morphology is discussed in light of this new grouping. Another clade, although weakly supported, is formed by representatives of Arctoteae, including the two South African genera Eremothamnus and Hoplophyllum. The latter two form a sister group with 100 % support.
TL;DR: The highly divergent sequences of Hydrostachys make phylogenetic placement difficult, but maximum parsimony and maximum likelihood analyses of combined data sets agree in placing HydrostACHys within Hydrangeaceae, as do separate analyses of rbcL, atpB, and the 5' portion of ndhF.
Abstract: Summary Albach, D. C., Soltis, D. E., Chase, M. W. & Soltis, P. S.: Phylogenetic placement of the enigmatic angiosperm Hydrostachys. - Taxon 50: 781-805. 2001. - ISSN 0040-0262. Hydrostachys, an enigmatic aquatic plant genus from Madagascar and southern to central Africa, has been suggested to be related to Lamiales based on embryology, whereas rbcL sequences have indicated a relationship with Hydrangeaceae (Corales). We investigated these hypotheses by combining rbcL with atpB and ndhF sequences and increased taxon sampling in Hydrangeaceae compared to previous analyses. Rates and patterns of molecular evolution vary across ndhF with the 3' portion giving a different result than the 5' portion. The highly divergent sequences of Hydrostachys make phylogenetic placement difficult, but maximum parsimony and maximum likelihood analyses of combined data sets agree in placing Hydrostachys within Hydrangeaceae, as do separate analyses of rbcL, atpB, and the 5' portion of ndhF. Few morphological and embryological characters support this relationship.