Showing papers in "Taxon in 1976"

Ecological Species, Multispecies, and Oaks

Abstract: Summary Oaks exemplify problems with the reproductive species concept which motivate a reconsideration of the use and nature of species. Ecology is important in the reconsideration. The species level is usually overemphasized in evolutionary thought; selection acts on phenotypes and any mutualistic units. Standard definitions tend to inhibit free conceptual progress. Multispecies, sets of broadly sympatric species that exchange genes, may occur among animals as well as plants and may conceivably bridge kingdoms. This phenomenon can be adaptively important. There may be taxa without species. The degree of modality of adaptive zones can be investigated empirically.

The terminology of leaf architecture

Abstract: Summary A comparative study of leaf architecture throughout the Angiosperms has been made and six classes of venation patterns are recognised. The terms employed are defined and arranged in a systematic order for convenience of reference. Some new terms have been introduced where greater precision was needed and for little known venation patterns.

Phenetic taxonomy at the species level and above

Abstract: Summary Phenetic analyses are valuable at all taxonomic ranks. A review of work at higher ranks is presented, and certain difficulties are discussed: these are just as serious for traditional studies, though often glossed over. Difficulties include determination of homologies, incompleteness of data and shortage of constant characters. It is also necessary to employ similarity coefficients and cluster methods that are not too sensitive, respectively, to effects of gross size and numbers of OTU's. The number of OTU's required to represent a homogeneous cluster is apt to be underestimated: even with a simplified model of phenetic variation this number should be at least io and preferably 25 or more. Some newer developments in numerical analysis of phylogeny are briefly reviewed. Phenetic taxonomy is now generally contrasted with phylogenetic taxonomy, and this was an essential idea in the original use of the term phenetic relationship by Cain and Harrison (I960) to mean overall similarity based on all available characters. They were speaking of the resemblance or similarity that was estimated from the observed features of organisms without reference to how these features had arisen in the course of evolution. It is now widely conceded that the bulk of taxonomic work is basically phenetic, and that phylogenetic deductions must be made from phenetic evidence. This has been most cogently

Autogenous theories for the origin of eukaryotes

Abstract: After a brief resume of the principal alternatives the author concludes that the only reasonable hypothesis for the fully autogenous development of the eukaryotes is that involving a cyanophyte-like photosynthetic ancestor: the "Uralga." A structurally explicit scenario for the internal events necessary to produce general eukarotic organisation within that framework is outlined. Central to the model is the progressive differentiation of membrane systems, leading to enclosure of specialised, double-membraned metabolic compartments by engulfment during the stage in which endoand exocytotic properties were attained. Some minor differences between this model and that of Cavalier-Smith (I975) are discussed. The paper concludes with some comments about hypotheses involving endosymbiosis, including the virtues of a compromise hypothesis in which mitochondria arose autogenously, but chloroplasts arose by endosymbiosis.

The subfamilial, tribal and subtribal nomenclature of the rubiaceae

Abstract: The Rubiaceae are one of the largest and most easily recognized angiosperm families, yet within this relative uniformity at the familial level is considerable generic diversity. Nearly all concerned taxonomists, commencing principally with de Jussieu (1789), grouped the genera into infrafamilial taxa, the number of which has varied from a traditional ten or thirteen to the twenty-five proposed by Hooker (1873), or more. The last comprehensive treatment of the entire family at the generic level is that of K. Schumann (I891), whose classification does not differ significantly from that of Hooker; it ultimately has its origins in the systematic scheme proposed by de Candolle (1830), A. Richard (1830), Endlicher (1838), and others. Only recently have the traditional criteria for the classification of the Rubiaceae been called into question by Verdcourt (1958) and Bremekamp (1966), the work of these two authors having stimulated considerable new interest in the suprageneric taxonomy of the Rubiaceae. This new interest has meant an increased use of names published at the ranks of subfamily, tribe, and subtribe. Unfortunately, earlier workers were somewhat less than careful in the use of such names, with the predictable results that many names commonly employed for taxa at the ranks below family and above genus are invalid or illegitimate. Especially disturbing are the facts that many modern authors persist in taking up incorrect names and in proposing new names without validly publishing them under the existing Code. The purpose of this study is to present in as compact a form as possible the nomenclatural status of all names published at those ranks under the Rubiaceae. It is a task made particularly difficult by the fact that such names are not accounted for in such compendia as Index Kewensis, a situation which makes considerable bibliographic work necessary. Consequently, a nomenclatural survey of this kind cannot in any way be definitive, since the totality of botanical literature cannot be (and has not been) exhaustively searched. It is felt, however, that in the present study

The evolution of karyotype and polyploidy in arboreal plants

Abstract: Although relatively few biochemical studies have been carried out on woody plants, interesting correlations (and discrepancies) have been noted between nuclear DNA content and several parameters such as geographic range (latitude), ecological adaptation, nuclear volume, and karyotypic differences such as chromosome length. Hybridization between genomes with complements possessing chromosomes of different relative sizes, B chromosomes, and repetitious DNA and heterochromatin, have been reasons advanced for changes in karyotypes and nuclear DNA response. B chromosomes may not be as rare in tree species as previously considered. It may be expected that DNA-RNA hybridization and Giemsa staining procedures will reveal differences in karyotypes between species in genera where genomes at present exhibit only moderate differences between species. While successful callus production has been induced for a number of woody species, so far no haploid trees have been produced. In Betula there appears to be little barrier to cross fertilization and plants with different euploid chromosome numbers have been obtained from seed from the same parental tree.

The taxonomic affinities of the australian neottioideae

Abstract: The taxonomic affinities of the Neottioideae (Orchidaceae) and, in particular, of its Australian members, have been examined, employing numerical taxonomic methods. Two analyses were carried out the first, discussed only briefly, involved a sample of the entire family and the second a sample of the Neottioideae as defined by the first analysis. The analyses were carried out by the Euclidean-based Group Average (or Mean Squared Distance) strategy and checked by means of a Principal Co-ordinate Analysis. The analysis of the Neottioideae indicated that this subfamily comprised two groups Diurideae, including the tuber-forming Australian taxa and the Neottieae which do not possess tubers and are cosmopolitan in distribution. A possible scheme of classification of the Neottioideae is presented and relationships within the group are briefly discussed.

A classification of plants into higher taxa based on cytological and biochemical criteria

Abstract: Summary A variety of schemes are employed currently for the classification of plants into higher taxa. The two most widely used schemes, the traditional kingdom Plantae with subkingdoms Thallophyta and Embryophyta, and the Whittaker five-kingdom system with plants in the kingdoms Monera, Protista, Fungi and Plantae, rely on nineteenth century morphological criteria for delimitation of taxa that result in polyphyletic assemblages of organisms. It is proposed that plants be assigned to seven kingdoms, subordinate to the superkingdoms Procaryota and Eucaryota which are based on the procaryotic and eucaryotic types of cellular organization. The distribution of accessory chlorophylls is used as a major taxonomic criterion for classifying photosynthetic organisms at the kingdom level. This results in a single kingdom, the Cyanochlorobionta for photosynthetic plants containing chlorophyll a only within the superkingdom Procaryota. Photosynthetic plants within the superkingdom Eucaryota have been divided into three groups, the kingdom Erythrobionta for organisms with no accessory chlorophyll or occasionally chlorophyll d (and lacking flagella), the kingdom Chlorobionta for organisms with accessory chlorophyll b, and the Ochrobionta for those organisms with accessory chlorophyll c. Vascular plants have been assigned to a single division, the Tracheophyta, since in addition to having a similar biochemistry (chlorophylls a and b, similar carotenoids, starch as a reserve food product) they possess also a basic morphological groundplan - a vascular system containing xylem and phloem, and a life history consisting of an alternation of generations. The fungi have been assigned three kingdoms as opposed to most extant schemes of classification in which they are allocated to a single polyphyletic assemblage. The true fungi have been divided into kingdoms Fungi I and Fungi 2 since it is thought that they have evolved from the Chlorobionta and Ochrobionta, respectively; the myxomycetes have been placed in a third kingdom, the Myxobionta. A perusal of eighteen botanical books published in the U.S.A. during the last decade has revealed a considerable lack of uniformity in the usage of the higher categories of classification: five used the traditional two kingdom system of organisms with the kingdom Plantae for plants and the subkingdoms Thallophyta and Embryophyta; three employed the recently proposed five kingdom organismic system of Whittaker (1969) with plants in the kingdoms Monera, Protista, Plantae and Fungi; six began their treatment at the division level, presumably due to lack of satisfaction with existing schemes; and two proposed new systems for the subdivision of the traditional kingdom Plantae, Bold (1973), who has been followed subsequently by two authors, established the subkingdoms Prokaryonta, Chloronta, and Achloronta, and Neushul (1974) the subkingdoms Prokaryonta and Eukaryonta. In the last few decades a tremendous accumulation of cytological and biochemical data has occurred (Klein and Cronquist, 1967), but these have not been adequately utilized in classification. With the recent publication of compendia