摘要:

SummaryApomixis is not necessary. Neither agamospermy, nor its common companion polyploidy, confer selective advantages on populations that are not equally well provided for in the diploid sexual breeding system. Yet, gametophytic apomixis is widely distributed among diverse families of flowering plants, and agamospecies are frequently as widely distributed as their most successful sexual relatives. The principal adaptive advantage of apomixis is that it can restore fertility in sexually sterile individuals. Polyploidy enhances interspecific hybridization, and it is among such hybrid complexes where apomixis is commonly encountered. Once established, apomixis contributes toward immediate fitness by fixing and reproducing advantageous genotypes. Continuous progressive evolution, however, depends on an essential equilibrium between sexual and asexual reproduction.

ISSN:0040-0262    

DOI:10.2307/1218426

出版商:Wiley    

年代:2019

数据来源: WILEY

ISSN:0040-0262    

DOI:10.1002/j.1996-8175.1974.tb02836.x

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryThe problem of representing within‐OTU character variability in numerical taxonomy is considered and the limitations inherent in the restriction to single values, for example means or more seriously exemplar individuals, are emphasised. Jardine and Sibson's distinction between the attributes of individuals and the characters of populations or taxa is considered a useful one in its emphasis on the different treatment required for the comparison of individuals as OTUs as against that of groups. Existing methods of handling character variation are outlined and their limitations discussed. A new method, the character‐state frequency procedure, which can readily be incorporated into existing programs, is described and its effects on the analysis of two sets of data are outlined.

ISSN:0040-0262    

DOI:10.2307/1218428

出版商:Wiley    

年代:2019

数据来源: WILEY

ISSN:0040-0262    

DOI:10.1002/j.1996-8175.1974.tb02838.x

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryEdge‐punched cards were used in a simple method to detect phenetic relationships among the 27 species ofSolanumsectionBrevantherum. Data from species descriptions were placed on two sets of punch cards, one for measuring the character correlations among species, the other for detecting modal character states of the group and helping with key construction. A matrix of phenetic similarity was compiled by sorting the deck of character cards and comparing each species with every other to determine the number of character states shared by species pairs. Simple analyses were performed which are expressed graphically. Phenetic distance of each species from a hypothetical ancestor is illustrated. Punch card methods have the advantage of allowing constant contact with actual character states during the study.

ISSN:0040-0262    

DOI:10.2307/1218430

出版商:Wiley    

年代:2019

数据来源: WILEY

ISSN:0040-0262    

DOI:10.1002/j.1996-8175.1974.tb02840.x

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryAn analysis of the different taxa ‐ orders, families, genera and species indicates that some concept of the latter three must have been formulated by man from the very early times where plants were first being domesticated. However, the generic concept seems to be the earliest and most basic. In the process of domestication the primitive man apparently picked plants on the basis of their features without discrimination as to species. Except in the case of monotypic genera or single species isolated from the main generic range, hybridization among species has played from the very beginning an important role in the origin of cultivation. As a result, in most cultigens, no single ancestral species would be traceable in later times and also it would be impossible to trace the origin of most of these plants to a single precise geographical center.

ISSN:0040-0262    

DOI:10.2307/1218432

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryAttention is drawn to the unsatisfactory nature of the suprageneric classification of the family Portulacaceae adopted in thePflanzenfamilien. A new arrangement is proposed in which seven tribes only are recognised; two of these, the Calyptrotheceae and the Calyptrideae, are new.

ISSN:0040-0262    

DOI:10.2307/1218433

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryOutcrossing rates in natural populations ofLupinus nanusDougl. have been found to vary from nearly zero to nearly 100 percent (Harding and Horovitz, 1969; Harding, 1970). These studies were based primarily on a group of northern populations of subspeciesapricus(Elliott, Harding, and Mankinen; paper VI). The purposes of this paper are (1) to report estimates of outcrossing for the other subspecies ofL. nanus, (2) to report estimates of outcrossing for the closely related species,L. bicolor, L. affinis, L. polycarpus, andL. pachylobus, (3) to discuss the relationship between these estimates of outcrossing and autofertility, and (4) to discuss the relationship between outcrossing and phenotypic and genotypic variability maintained in populations.

ISSN:0040-0262    

DOI:10.2307/1218434

出版商:Wiley    

年代:2019

数据来源: WILEY

ISSN:0040-0262    

DOI:10.2307/1218435

出版商:Wiley    

年代:2019

数据来源: WILEY