摘要:

SummaryOur knowledge of patterns of variation and evolution in groups of allied species of the north temperate flora is gradually increasing; but relatively few groups have been studied cytotaxonomically or analysed genomically. Data for three groups of species, in the generaViola, MaianthemumandPolypodium, are reviewed, and resemblances and differences between them discussed. The importance of further biosystematic work of this kind, including ecological as well as taxonomic studies, and organised on an international basis, is pointed out.

ISSN:0040-0262    

DOI:10.2307/1219442

出版商:Wiley    

年代:2019

数据来源: WILEY

ISSN:0040-0262    

DOI:10.1002/j.1996-8175.1976.tb00399.x

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryOaks 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.

ISSN:0040-0262    

DOI:10.2307/1219444

出版商:Wiley    

年代:2019

数据来源: WILEY

ISSN:0040-0262    

DOI:10.1002/j.1996-8175.1976.tb00401.x

出版商:Wiley    

年代:2019

数据来源: WILEY

ISSN:0040-0262    

DOI:10.2307/1219446

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryAn index for comparing weediness in plants can be constructed from site information on herbarium specimen labels. The percent of the species collected from disturbed sites is a measure of weediness. Some examples are presented inCerastium, Polygonum, andAster.

ISSN:0040-0262    

DOI:10.2307/1219447

出版商:Wiley    

年代:2019

数据来源: WILEY

ISSN:0040-0262    

DOI:10.1002/j.1996-8175.1976.tb00404.x

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryIt is shown how principal component analysis can be extended to allow for multi‐state discrete characters as well as continuous characters. When all the characters are discrete, the proposed extension reduces to correspondence analysis. A taxonomic example is given to illustrate the method in practice. The technique allows the estimation of a taxonomic distance between objects which have been scored for multi‐state characters. However, taxonomic structure may be better inferred directly from the ordination, rather than by constructing a taxonomic distance measure.

ISSN:0040-0262    

DOI:10.2307/1219449

出版商:Wiley    

年代:2019

数据来源: WILEY

ISSN:0040-0262    

DOI:10.1002/j.1996-8175.1976.tb00406.x

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryAn approach to character assessment is proposed in which states within characters are weighted. It is suitable for use with Gower's general coefficient of resemblance. Values of character‐states are determined intuitively or through appropriate transformations. The aim of this approach is to incorporate information available on the relative closeness of the states, into classificatory studies. This information usually becomes lost at the coding stage because of the practice of equidistant states.

ISSN:0040-0262    

DOI:10.2307/1219450

出版商:Wiley    

年代:2019

数据来源: WILEY