Chromosome Studies in Asteraceae from the United States, Mexico, the West Indies, and South America

Chromosome counts of Asteraceae are reported from Mexico, the United States, the West Indies, Peru, and Bolivia. First counts are reported for 27 species, eight infraspecific taxa, and three interspecific hybrids in Brickellia, Chrysanthellum, Cirsium, Egletes, Erigeron, Flaveria, Gnaphalium, Heterotheca, Hieracium, Hymenothrix, Koanophyllon, Layia, Lessingia, Pectis, Sclerocarpus, Stuessya, Tagetes and Wedelia. Counts are also reported for 196 taxa or hybrids for which chromosome numbers have been published previously. Of these, nine are new numbers. Taxonomic implications of certain counts are discussed. THIS PAPER is a continuation of studies (Keil and Stuessy, 1975, 1977; Keil and Pinkava, 1976, 1979, 1981; Keil, 1977; Pinkava and Keil, 1977) on chromosome numbers in Asteraceae. Vouchered chromosome counts represent both hitherto unreported taxa and taxa for which counts have been published previously. The former counts serve to increase the number of taxa for which cytological data are available and can provide insights into relationships and patterns of evolution. The latter counts provide information about variation in chromosome complements and broaden the geographical sample of the various taxa. METHODS-Immature capitula were killed and fixed in modified Carnoy's fixative [4-6 chloroform: 3 ethanol: 1 glacial acetic acid, v:v: v]. Florets were stained in either iron-acetocarmine or Snow's stain (Snow, 1963) and anthers or whole florets were squashed in a drop of Hoyer's medium in a modification of the methods of Beeks (1955). Chromosome counts and meiotic behavior were ascertained from I Received for publication 17 March 1987; revision accepted 14 July 1987. Research was supported by NSF Grant DEB 81-04683. We thank John Popenoe, Director of the Fairchild Tropical Gardens, for making facilities available during Dr. Keil's field work in the West Indies; and George Proctor and Peter Bretting for assistance in the field in the Dominican Republic and Jamaica, respectively; Judith M. Canne for providing bud samples from Bolivian plants; Michael 0. Dillon for providing seeds of Peruvian plants; and John C. Semple for determinations for Heterotheca and Pityopsis species. We particularly thank R. K. Brown for allowing us to publish results from his research on Tragopogon. We thank Billie L. Turner, John C. Semple, and John L. Strother for reviewing the manuscript. meiotic microsporocytes and were documented by camera lucida or free-hand drawings. Voucher specimens, microslides, and drawings are deposited at ASU and OBI. Percent pollen stainability, based on 500 grain samples stained in aniline blue in lactophenol, was calculated for some plants. RESULTS-The chromosome counts obtained are listed in Table 1. First counts are reported for 27 species, eight infraspecific taxa, and three interspecific hybrids; counts are also reported for 196 additional taxa or hybrids for which counts have been published previously. Eight of these are new numbers. DISCUSSION-As in previous papers, the discussion is restricted to first or new counts or significant comments. The sequence of Table 1 and the accompanying commentary is alphabetical by tribe. AstereaeOur report of 2n = 9II for Egletes prostrata and the only previous report for the genus, n = 27 for E. viscosa (L.) Less. var. dissecta Shinners (Keil and Stuessy, 1977), support a base number of x = 9 for the genus. Our first report of 2n = 911 for Erigeron bellioides is in accord with the established base number, x = 9, for Erigeron. The head morphology of this diminutive plant, however, suggests that it might better be placed into Conyza, which has the same base number. Cronquist (1943) listed the following features as diagnostic for Conyza: "Central hermaphrodite flowers few; pistillate flowers numerous, with filiform corollas; ligules, if present, inconspicuous, shorter than the tubes and scarcely if at all exceeding the pappus." The heads