Showing papers in "Taxon in 1971"

Toward a rational classification of cultivated plants

Abstract: The methods of formal taxonomy have not been very satisfactory for the classification of cultivated plants. As a result, the people who deal with cultivated plants the most have developed their own informal and intuitive classifications based on experience as to what constitutes useful groupings. An attempt is made to provide a framework in which both systems can operate with a minimum of confusion. The structure of the total available gene pool is characterized by assigning taxa to primary, secondary and tertiary gene pools. At the infraspecific level, cultivars are grouped into races and subraces in an informal way without rigid rules for the use of terms.

Annual review of ecology and systematics

Abstract: This book contains proceedings of the Annual Review of Ecology and Systematics. Topics covered include: global change, world environment, ecology, ecosystems, interactions, pollutants and climatic change. with Volume 23 the succession from the pioneers to the next seral stage has been completed. This seems an appropriate opportunity to renew the invitation to members of the ecology and systematics communities last issued in Volume 14 (1983) for suggestions for reviews that we might not think of soliciting ourselves. The names of the spine and title have changed, bust the objectives have not.

The use of plant indicators in ground water surveys, geologic mapping, and mineral prospecting

Abstract: Summary The use of vegetation in interpreting geological phenomena is becoming an important tool in the search for ore deposits that are buried under thick soil cover or layers of unmineralized rock. Species assemblages and plant density are useful in mapping geologic strata of different chemical composition and reservoir capacity. Hidden ore deposits can be located through chemical analysis of plant tissue, by mapping the distribution of species, and by observing toxic effects caused by an excess of metals as well as signs of faulty nutrition or deranged metabolism in plants whose roots are in contact with ore. Plant indicators of ore deposits may be species that are adapted to living exclusively on rocks or soils that supply unusual amounts of a particular element, or they may be species of wide distribution that favor mineralized ground under certain local conditions because of a change in acidity or availability of major plant constituents. Plants that are not highly tolerant of metals in an ore assemblage may exhibit toxicity symptoms or be completely absent over ore. Geobotanical techniques of mapping indicator plant species and communities, combined with observation of changes in plant appearance can aid the geologist in prospecting for hidden ore deposits.

The cytogeography of the loranthaceous mistletoes

Abstract: Known chromosome numbers in the Loranthaceae are reviewed and 102 new records added. The basic number of the family is x = 12 and there has been progressive aneuploid reduction to x = 8. The early development of the family has been under temperate conditions in the Southern Hemisphere, where stocks with x = 12 and 11 became established in temperate South America and Australasia. Rapid aneuploid reduction continued after the establishment of strong continental isolation, establishing numbers of x = 9 and 8 in the Old and New Worlds respectively. Massive secondary radiation in the tropics has followed, involving the 12-, 9and 8-paired stocks. Increase in chromosome size occurred during the tropical radiation, perhaps compensating for loss of recombination potential due to aneuploid reduction. Polyploidy is a rare and recent phenomenon in the history of the family, being documented in only two Central American taxa. One of these may be an autoploid.

Chromosome numbers in the meliaceae

Abstract: Summary A detailed chromosome study has been made of 58 species in 30 genera of the tropical family Meliaceae. The results largely confirm observations, by other investigators on similar tropical woody groups, that high chromosome numbers are common and that polyploidy is a frequent phenomenon. Although the chromosomes are, in most species, very small and metacentric, some differences in chromosome size and shape are detectable. Many genera seem to have a high base number and/or several different numbers. The Meliaceae, unlike some other tropical woody groups, are particularly interesting because of the considerable range of chromosome numbers they exhibit. Differences in number have been observed between even closely related species in the economically important timber genera Swietenia, Cedrela and Toona, and this has an obvious bearing on future tree breeding and tree improvement studies. The taxonomic significance of chromosome numbers is discussed. The Meliaceae, one of the larger, exclusively woody, Angiosperm families, whose range extends throughout the tropical and subtropical regions of the world, has been the object of intensive monographic study in the Forest Herbarium at Oxford during the last decade. The subfamily Swietenioideae (including Cedreloideae) has been the particular interest of one of us (BTS), who (with White) has also revised most of the species in the family for the continent of Africa. A conspectus of the family at the generic level by Pennington, Styles and White is soon to be published; in it 52 genera are accepted. The number of species is difficult to estimate but at least 1000 are thought to exist. Many are large or very large trees and are major constituents of primary and secondary rain forest and various types of woodland. Some are the source of high-grade timbers of economic importance, e.g. species of Swietenia, Cedrela, Khaya, Entandrophragma, etc. Some of them, and others such as Azadirachta, are proving important as plantation crops, and the selection and breeding of phenotypically superior strains has been started by Forest Departments as part