Cytogeography of Claytonia virginica and Its Allies

Abstract

On the basis of chromosome numbers from more than 1,000 individuals of Claytonia virginica L. (Portulacaceae) throughout its range, a complex evolution of major cytotypes is discussed in relation to distribution and morphology. Chromosomal diversity is thought to have evolved from a base of n 6 by hyperaneuploidy to n 7 and 8 with each race giving rise to widespread and dominant primary tetraploids (n 12, 14, 16). These in turn, and largely by hypoaneuploidy, formed many secondary tetraploid races, the most significant of which are n = 11 and 15. Higher polyploids from 6x to 12x where x = 6, and 6x and 8x where x = 7 are also discussed. Infraspecific phylogeny is compared with data for two allied species, C. caroliniana Michx. and C. lanceolata Pursh, which show striking parallels with C. virginica in chromosomal evolution. By one morphological character, leaf width, the cytotypes separate into two groups, not along diploid vs. polypoid lines, but rather a narrow-leafed var. acutiflora DC. with n = 6, 7, 12?, and 14? and a broad-leafed var. virginica with n = 8 and 16?. From collections made throughout eastern North America over 1,000 plants of Claytonia virginica L. (Portulacaceae) have been examined chromosomally. With the exception of Rothwell (1959) earlier studies have been limited in scope although all have made a substantial contribution to a cytogeographic understanding of the species (Bell, 1965; Davis & Bowmer, 1966; Lewis, 1959, 1962, 1967; Lewis et al., 1962, 1967; Rothwell & Kump, 1965). While these studies illustrated a wide diversity of chromosome number for C. virginica (2n12 to ca 191) none was extensive enough to indicate total distribution of all major cytotypes; rather only for a few from very limited areas, viz. dominance of x 7 in eastern Texas (Lewis, 1962), x = 8 in Indiana (Rothwell, 1959), and n= 12 and 15 in the St. Louis, Missouri area (Lewis et al., 1967). We shall attempt with our additional data to present the distribution of cytotypes occuring in the eastern half of the continent and to suggest their probable evolution. Cytogeography and evolution of C. virginica will be compared with several allied species as well as briefly with the primitive species of Claytonia. In addition gross morphological diversity will be correlated with the various cytotypes and discussed in relation to distribution. Cytological procedures followed those of Lewis (1962) and voucher specimens for each population were collected and are housed in the Missouri Botanical Garden herbarium (MO). 'Senior Fellow and Research Associates, Center for the Biology of Natural Systems, supported by Public Health Grant No. 1 P10 ES 00139-01 ERT. ANN. MISSOURI BOT. GARD. 54(2): 153-171, 1967. This content downloaded from 207.46.13.113 on Wed, 05 Oct 2016 04:20:10 UTC All use subject to http://about.jstor.org/terms [VOL. 54 154 ANNALS OF THE MISSOURI BOTANICAL GARDEN