A disturbed lowland population of Claytonia virginica has diploid, triploid, and tetraploid races as well as numerous aneuploids, particularly at the tetraploid level. Most tetraploids were represented by a stabilized dysploid race. Coexistent adaptation has been possible at least in part because temporal niches vary between the dominant polyploid races, and perhaps between them and the diploid, in an environment well removed from the original boreal habitat. The activity aboveground of the spring ephemeral Claytonia virginica Linnaeus (Portulacaceae) is restricted in northern deciduous forests to a period between snow melt and forest canopy development. Its phenology and productive capacity closely adapt the species to this temporal niche in its northern distribution where only diploid individuals predominate (Lewis & Semple, 1977). Throughout midlatitude and southern ranges the species thrives in disturbed and weedy habitats beyond the forest and concomitantly has a prolonged period of flowering. Such populations are very variable chromosomally; a cytoecological consideration of one population found in a public park in St. Louis as a part of a flat, grassy lowland with a few large cottonwoods (Populus deltoides Marshall), an area about 40 m by 20 m, is the basis for this paper. Weekly between 24 February and 10 April 1976, seven samples of inflorescences were fixed in modified Carnoy's solution during an unusually extended flowering period. Material was stored at -20?C for varying periods up to four months before staining in 1% acetic-orcein. Meiosis of microsporocytes was recorded, and it provided an estimate of the chromosomal composition of the population in relation to time as well as an indication of meiotic behavior of individuals. In addition, pollen stainability and seed formation were observed for field collections. The populations separated chromosomally into three main ploidy levels (Table 1; Fig. 1): diploidy, largely of eudiploids (n = 8, 2n = 16), but also including an aneudiploid (2n = 17); triploidy, also mostly of eutriploids (n = 12, 2n = 24), but having a few aneutriploids (2n = 23); and tetraploidy in which the eutetraploids (n = 16, 2n = 32) were in the minority (11.6%) whereas the reduced aneutetraploid n = 15 was by far the most frequent cytotype (68.1%), followed by other aneuploids (2n = 28, 29, 31, 33), all 1 This study was supported by National Science Foundation grant DEB76-009978. I thank Mike J. Furniss, Diana L. Pollock, Tim B. Powers, James C. Solomon, Laura A. Sunn, Helen J. Young, and Linda L. Zurfluh for assistance in the field and laboratory. 2 Biology, Washington University, and the Missouri Botanical Garden, St. Louis MO 63130. This content downloaded from 207.46.13.28 on Wed, 31 Aug 2016 04:08:51 UTC All use subject to http://about.jstor.org/terms 1976] LEWIS: TEMPORAL ADAPTATION AND PLOIDY 341
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Walter H. Lewis (1976) studied this question.