Chromosome numbers in Sphaeralcea section Fendlerianae

Chromosome numbers are reported for ten taxa in Sphaeralcea section Fendlerianae (Malvaceae). New ploidy levels are reported for six taxa, with one species not previously reported, and extensive polyploidy at all taxonomic levels is documented. The geographic and taxonomic distribution of polyploids suggests that polyploidy arose many times in the taxa of Sphaeralcea. Sphaeralcea fendleri var. venusta, S. polychroma, and S. wrightii populations have yielded exclusively tetraploid counts. Tetraploidy is correlated with taxa having lavender petals. Polyploidy has also allowed the taxa to expand their distributions without resulting in speciation. SPHAERALCEA WAS LAST revised by Keamey (1935) to include over 50 taxa. At that time, very little was known about the chromosomal variation in the group. The most comprehensive study of chromosome numbers in North American Sphaeralcea was by Webber in 1936, in which the chromosome numbers of Iliamna, Malvastrum, Meliphlea, Phymosia and Sphaeralcea were compared. Haploid numbers of 5, 10, 15 and 25 were found in the taxa of Sphaeralcea, and clear delimitation was made between Sphaeralcea and the other genera. Since that time, sporatic reports have been published on the chromosome numbers in I Received for publication 11 October 1985; revision accepted 19 March 1986. I wish to thank Tim Remple for his tireless assistance in slide projection, Tod Stuessy for his comments on the manuscript, and the curators of those herbaria giving permission to remove seeds for germination B. Bartholomew (DS), B. Burger (F), P. Holmgren (NY), C. Mason (ARIZ), N. Morin (MO), D. Northington (TTC), M. Powell (SRSC), R. Spellenberg (NMC), and B. Turner (LL). Funding for this research was provided by The National Science Foundation through grant DEB 81-21906. Sphaeralcea taxa (Darlington and Wylie, 19 5 5; Krapovickas, 1957; Powell and Powell, 1977; Weedin and Powell, 1980; Ward, 1983; La Duke, 1985) but generally without taxonomic or evolutionary interpretation. Webber (1936) has shown evidence for diploid and tetraploid chromosome numbers within species and varieties of the same species within section Fendlerianae of Sphaeralcea (Table 1). He found no relation between the taxonomy of the group and the distribution of chromosomal variation. Subsequent reports for section Fendlerianae (Table 1) have contributed little to determining the extent of chromosomal variation in this section or how this variation may contribute to an understanding of the taxonomy of the group. This study was initiated in an attempt to determine the value of chromosome number for the taxonomy of this section. MATERIALS AND METHODS-Chromosome numbers from Sphaeralcea taxa were determined using meiotic or mitotic preparations following procedures outlined in Snow (1963) TABLE 1. Previous chromosome numbers in Sphaeralcea section Fendlerianae Chromosome Taxon number Reference S. angustifolia (Cav.) Don n = 10 Weedin and Powell, 1980 S. angustifolia var. cuspidata Gray n = 5, 10 Webber, 1936 2n = 10 Krapovickas, 1957 S. angustifolia var. oblongifolia (Gray) Shinners n = 10 Webber, 1936; Ward, 1983 S. fendleri Gray n = 5 Webber, 1936; Weedin and Powell, 1980 n = 10 Webber, 1936 2n = 15 Darlington and Wylie, 1955 S. fendleri var. albescens Keamey n = 5 Webber, 1936 S. fendleri var. venusta Kearney n = 10 Webber, 1936 S. incana Torrey in Gray n = 5, 10 Webber, 1936 S. incana var. cuneata Keamey n = 10 Webber, 1936 S. polychroma La Duke 2n = 20 La Duke, 1985