Distribution of Tetraploid and Diploid Tradescantia ohiensis in Michigan and Adjoining Areas

Abstract

Tradescantia ohiensis exists in a wild state in a diploid form and a tetraploid form which cannot be distinguished by morphological criteria. This paper reports the detailed distribution of diploid and tetraploid T. ohiensis. Since the area studied includes the northern limit of the range of the species and is far from its center of distribution, it seems a significant area in which to study the role of polyploidy in distribution. Edgar Anderson has made extensive studies of the distribution of diploid and tetraploid Tradescantia ohiensis (summarized in Anderson, 1954). He found tetraploids to predominate throughout most of the United States east of the Great Plains. He found diploids most abundant in Texas where diploids of other species of Tradescantia are centered, but he also found diploids in isolated areas of Indiana, Iowa, Kentucky, Michigan, and Louisiana. Except for diploid plants near the outer edges of the range of the species, the pattern of distribution plotted by Anderson in T. ohiensis (and in other species with both diploid and tetraploid races) suggested that the more aggressive tetraploids spread great distances from the place where the original doubling occurred, while the less adaptable diploids remained near the center of distribution of the species. The presence of diploids near the periphery of the range, however, is not explained by the above assumption alone. The area (outlined with stippling, Fig. 1) studied intensively by the author includes lower Michigan and enough of Indiana and Ohio to furnish a unit of investigation. On the basis of a study of herbarium records, and after intensive efforts to find the species growing farther north, the author is convinced that the northern limit of the distribution of the species is essentially as shown in Figure 1. Determinations of chromosome number were made from acetocarmine squashes of dividing microspores and microspore mother cells. Occasionally determinations were made from examination of hydrolized root and leaf meristems. Much of the determination was done in the field where the plants were collected, though many chromosome numbers were ascertained from plants taken to the laboratory.