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The Bases of Angiosperm Phylogeny: Cytology

Peter H. Raven
Annals of the Missouri Botanical Garden
Vol. 62, No. 3, The Bases of Angiosperm Phylogeny (1975), pp. 724-764
DOI: 10.2307/2395272
Stable URL: http://www.jstor.org/stable/2395272
Page Count: 41
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The Bases of Angiosperm Phylogeny: Cytology
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Abstract

A broad review of chromosome numbers in the angiosperms is presented according to the phylogenetic system of Cronquist. Consideration of the results indicates that the original basic chromosome number for the class as a whole, and for all but one of its subclasses, is or may well be x = 7. For Caryophyllidae, x = 9 is indicated. Families and taxa of higher rank can be compared only if the original basic chromosome number for the group is known, and there are many families where this is not the case. Evolutionary changes in chromosome number and morphology, particularly in herbaceous plants, have tended to give the impression that these characteristics were of limited utility in classification, and have often led to numerical coincidences between unrelated groups. In addition, many inaccurate counts have been reported, and vouchers, if present, are occasionally misidentified, giving rise to misleading conclusions. Electronic data processing should be applied to the field as soon as possible for efficient information retrieval, especially since the number of chromosome counts reported is growing annually. Well edited regional treatments, or those dealing with a particular taxonomic group, are encouraged. An initial burst of polyploidy is suggested for the angiosperms by the survival of many polyploid lines, especially among Magnoliidae and Hamamelididae. Although many families and even orders are of polyploid origin, progressive evolution in the group seems to have proceeded largely at the diploid level, and much of the major differentiation evidently occurred even among plants with the original basic chromosome number, n = 7.

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