CHROMOSOME NUMBERS IN THE COMPOSITAE. XIV. LACTUCEAE

Reports of 150 original chromosome counts are recorded, including reports of 22 genera and 57 species and subspecific taxa in tribe Lactuceae. Also included are first reports for 12 specific or subspecific taxa. x = 9 appears to be the ancestral base of the tribe. Chromosome numbers are known for over 85% of the genera of the tribe and the frequency of polyploidy is ca. 23%, which is about one-half that of the angiosperms. THIS iS the fourteenth of a series of papers reporting chromosome numbers in the Compositae (Raven et al., 1960; Raven and Kyhos, 1961; Ornduff et al., 1963; Payne, Raven, and Kyhos, 1964; Solbrig et al., 1964; Ornduff et al., 1967; Solbrig et al., 1969; Solbrig et al., 1972; Anderson et al., 1974; Powell, Kyhos, and Raven, 1974, 1975). It is the first of this series to be devoted to tribe Lactuceae. As in previous papers, the chromosome counts reported here represent a compilation of independent work by the several authors. Unless otherwise indicated, the counts were determined from aceto-carmine squashes of microsporocytes collected in the field. Voucher specimens for all counts have been deposited in the Dudley Herbarium of Stanford University unless otherwise indicated by the standard abbreviations in Table 1. Collection numbers preceded by C are by Chambers and those preceded by R are by Raven. RESULTS-In Table 1, we present 150 original chromosome counts for 22 genera and 57 species, subspecies, or varieties. These counts include first reports for taxa (indicated by asterisks). The novelty of these reports was checked by a survey of the chromosome number indices (Darlington and Wylie, 1956; Cave, 1956-1964; Ornduff, 1965-1967; Moore, 1973, 1974; Boll Received for publication 24 May 1976; revision accepted 4 October 1976. Contribution no. 1275 j, Division of Biology, Kansas Agr. Exp. Station, Manhattan 66506. This study supported in part by National Science Foundation grant BMS75-21300 to the senior author. We wish to acknowledge John Strother and David Keil for contributing chromosome counts; and James Henrickson, Clark Cowan, Dale Smith and John Thomas for sending us fixed plant materials. khovskikh et al., 1969) and other recent literature. Most of the counts presented here are consistent with previous reports and base numbers already established in the tribe. Exceptions to this are our reports of n = 10 in Agoseris apargioides, and n = 9 for A. apargioides ssp. maritima, and 2n 27 in Microseris sylvatica. The count of n = 10 (a pair of supernumerary chromosomes? ) in Agoseris apargioides is not in agreement with the 2n = 36 reported by Stebbins, Jenkins, and Walters (1953), nor with the n = 9 reported here for ssp. maritima. The triploid report for Microseris sylvatica (2n = 27) is the first polyploid encountered in subgenus Scorzonella; the plants were seed-sterile but reproduced vigorously by sprouts from the roots. DISCUSSION-The Lactuceae are well known chromosomally as a result of the early impetus from work on Crepis and its relatives by Babcock, Stebbins and their co-workers. Chromosome numbers have been reported for 60 of the ca. 70 genera in the tribe. The genera yet to be counted are Acanthocephalus, Dianthoseris, Epilasia, Faberia, Heteroderis, Hymenonema, Picrosia, Soroseris, Thamnoseris and Tourneuxia. Most of these are small central Asian genera. There has not been a survey of chromosome numbers of the entire tribe since the classic paper by Stebbins et al. (1953), but still the Lactuceae rank as perhaps the cytotaxonomically best known tribe in the family. The chromosome numbers reported here and in the period since 1953 tend to support most of the phyletic conclusions of Stebbins et -al. (1953)-a relatively low frequency of polyploidy, frequent descending aneuploidy and an ancestral base chromosome number of x = 9.