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Chromosome Number, Polyploidy, and Growth Habit in California Weeds
Charles B. Heiser, Jr. and Thomas W. Whitaker
American Journal of Botany
Vol. 35, No. 3 (Mar., 1948), pp. 179-186
Published by: Botanical Society of America, Inc.
Stable URL: http://www.jstor.org/stable/2438241
Page Count: 8
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On the basis of an analysis of chromosome number, polyploidy and growth habit in a selected list of 175 species of weeds of California, the following facts become apparent: There are about equal numbers of diploid and polyploid species among the weeds of California. This fact suggests that in general polyploidy is an unimportant factor in determining whether a particular species will become an effective weed. Weedy species of California are characterized by a slight excess of annuals. In the monocotyledons, annuals and perennials are found in about equal numbers, while the polyploids are greatly in excess of the diploids (65 per cent to 35 per cent). In the dicotyledons, no such great difference is evident. The Compositae and Gramineae compose about two-fifths of our list of weedy species, with thirty-seven and thirty-six species, respectively. In both families there is strong evidence that the annual growth habit contributes towards making a species a successful weed. The chromosome numbers of eighteen species of weeds are reported for the first time. Approximately 40 per cent of the chromosome counts listed in table 4 are from California material. Generalizations involving polyploidy are probably meaningless. Its significance can only be evaluated by the examination of individual families or even genera, rather than floras as a whole.
American Journal of Botany © 1948 Botanical Society of America, Inc.