Showing papers in "Taxon in 1984"

A simple method for establishing taxonomic characters from measurement data

Abstract: A simple method is described for defining multi-state taxonomic characters from measurement data. Bar diagrams are used to observe the pattern of variation of the measurements both within and between the units to be classified. The method gives definitions which are superior to arbitrary subdivisions of the range both in revealing taxonomic correlations and in reducing the effects of sampling error.

The role of hypothesized direction of characters in the estimation of evolutionary history

Abstract: Summary The effect of directing characters on cladistic analysis is discussed. Characters can conflict because of the character state membership of the EUs, the ordering of character states, or direction. Conflicts of characters were analyzed in twenty-three data sets containing a total of 1024 characters. At least 93 percent of character conflicts in these data sets were not due to incorrectly hypothesized direction. Most character conflicts are caused by similarities among EUs that are due to parallelisms or reversals that were not recognized by the systematist. Arguments against a priori directing of characters are presented. It is recommended that an undirected analysis be performed first and that the undirected tree be directed subsequently. To document and explain the diversity of organisms is one of the fundamental goals of biology. The theory of evolution provides a general explanation of the mechanism that created the multitude of life forms that inhabit the earth today. Many systematists are currently interested in the possibility of reconstructing the evolutionary history of organisms from the attributes they possess. The development of an objective basis for estimating the branching pattern of evolutionary history is the concern of cladistics, a subdiscipline of quantitative systematics. Several recent authors (Crisci and Stuessy, 1980; Stevens, 1980; Watrous and Wheeler, 1981; see Stevens, 1980 for earlier references) have discussed the problem of determining the evolutionary direction of character trends. These authors consider the designation of an ancestral state a "critical first step" in the estimation of evolutionary history. Many systematists presume that cladistics requires the use of directed characters and that any method that does not require hypothesized evolutionary direction of characters is phenetic. An evaluation of the contribution that character direction makes to the estimation of evolutionary history is therefore in order.

Micromolecular patterns and the evolution and major classification of angiosperms

Abstract: Summary Integration of morphological and micromolecular data sets into a single system of classification is a major challenge facing the plant systematist of our time. Here an attempt is made to this end with regard to the upper levels of angiosperm classification. In particular, natural products which derive from the shikimate pathway are considered. Their distribution and biosynthesis demonstrates the existence of micromolecular links between the magnoliid, caryophyllid and monocotyledonous families, thus paralleling morphological characters. Chemical evidence is also in favour of the earlier idea that the largest gap within angiosperms is not that between dicotyledons and monocotyledons, but one that separates magnoliid, caryophyllid and monocotyledonous families (the "magnolialean block") from the rest of the dicotyledons (the "rosiflorean block"). However, in contrast to some previous authors, here the monocotyledons are found to encompass a homogeneous, morphologically clearly delimited assemblage. Anomalous occurrences of micromolecules, such as ellagitannins in the Nymphaeales, are discussed and the importance of chemically discordant characters for the recognition of convergences is emphasized. A biosynthetic extrapolation indicates that the early angiosperms were characterized by a full-fledged expansion of the shikimate pathway and a broad oxidation-reduction potential. These properties permitted the production of the neolignans, oxidative coupling products of allyl- and propenylphenols, and of 1,3-diarylpropanes, highly reduced flavonoid types. From here, stepwise suppression of the shikimate pathway must have led to the utilization of intermediates of this pathway characterized by higher oxidation levels, and finally to a total blocking of the shikimate pathway for the synthesis of micromolecules. It is hypothesized that the broad oxidation-reduction potential of the angiosperms and the full expansion of the shikimate pathway present at the beginning of their evolutionary history provided a much greater capacity of micromolecular variation than was present in other plant groups and thus contributed significantly to their evolutionary success.

Chromosome number reports LXXXV

Abstract: Series de nombres chromosomiques concernant des especes appartenant aux: Crassulaceae, Solanaceae, Cruciferes, Labiatae, Liliaceae, Gramineae, Cyperaceae, Papaveraceae, Chenopodiaceae, Fagaceae, Leguminosae, Bromeliaceae, Tamaricaceae, Zygophyllaceae, Dipsacaceae, Linaceae, Ronunculaceae, Rosaceae

Paralectotype, a new type term in botany

Abstract: Like Centotheca and Pseudelephantopus above, this is a proposal to conserve a commonly used spelling over the original spelling. Hapale, derived from the Greek for soft or tender, was changed by Schott himself a year later to avoid confusion with the zoological name Hapale for a genus of S. American marmosets. In this case it was agreed in the Committee (including the proposer) that Hapaline Schott 1858 is to be regarded as a nomen novum for Hapale Schott 1857, and without conservation some five or six new combinations under Hapale would be required. Despite the rather small size of the genus, this point seems to have tipped the balance in favour of the proposal, and it is recommended that Hapaline Schott be conserved over Hapale Schott.

A critique of Wagner groundplan-divergence studies and a comparison with other methods of phylogenetic analysis

Abstract: Revue et critique des articles ayant utilise cette methode. Farce et faiblesse des criteres utilises, propositions d'amelioration de la methode