CHROMOSOME NUMBERS OF T. I. Chuang2 and L. R. Heckardt3

Meiotic chromosome numbers in Castilleja are reported for 105 collections representing 34 species, mostly from Mexico, with a few from Central America and South America. Chromosome numbers of the following 19 species are reported here for the first time: C. bryantii, C. ecuadorensis, C. fissifolia, C. fruticosa, C. gracilis, C. hirsuta, C. integrifolia, C. irazuensis, C. linifolia, C. nubigena, C. ornata, C. ortegae, C. purpusii, C. roei, C. scorzonerifolia, C. stenophylla, C. talamancensis, C. tenuifolia, and C. virgata. Of the 34 species, 24 are exclusively diploid (n = 12); five are tetraploid (n = 24) only; two are octoploid (n = 48) only; three have two or more levels of ploidy (n = 12, 24, and 72). These polyploid species (including C. aspera, C. integrifolia, and C. tenuiflora) are the most troublesome taxonomically and substantiate our contention that polyploidy and hybridization are largely responsible for the complex morphological variation found in Castilleja. It is estimated that only 25% of Mexican elements of Castilleja (excluding C. affinis and C. subinclusa) exhibit polyploidy, in contrast to more than 50% polyploidy in western North American representatives. unusual chromosome number of n = 10 in the closely related C. gracilis and C. tenuifolia is postulated to be an aneuploid reduction from an n = 12 progenitor. role of chromosome number, especially polyploidy, in the evolution of Castilleja and its taxonomic significance is indicated for individual species. This paper represents the fourth in a series of reports on chromosome numbers in Castilleja (Scrophulariaceae) and is part of our continuing effort to furnish evidence of the significance of polyploidy and accompanying hybridization in forming the complex patterns of variation that characterize the genus. It is also our intention to clarify taxonomic and evolutionary relationships among its members. Our emphasis in this report is on those species occurring in Mexico, Central America, and South America. Castilleja (Indian Paintbrush) comprises over 200 perennial and annual hemiparasitic species. They are almost all American with their heaviest concentration in western North America, where they have been a continual source of extreme taxonomic difficulty, perhaps due partly to the prevalence of weak barriers to natural hybridization and associated polyploidy. Asa Gray's (1862) comment remains discouragingly prophetic: The species of this genus are most troublesome and unsatisfactory, not only on account of the difficulty of investigating the dried specimens, but also from the variability of the characters which have been relied upon in arranging them, and especially of the calyx. Heckard (1968) reported chromosome numbers of 54 taxa in Castilleja, largely of the Pacific Coast states and Mexico. Heckard & Chuang (1977) reported chromosome numbers of 35 taxa from the Great Basin and Rocky Mountains, and Chuang & Heckard (1982) reported 13 taxa of annual Orthocarpus (sects. Castillejoides and Cordylanthoides) mainly from California, which have recently been merged into Castilleja subg. Colacus sect. Oncorhynchus (Chuang & Heckard, 1991). Our continuing survey of chromosome numbers in the genus in western North America (Heckard, ' We are deeply grateful to Robert W. Cruden in particular, and Dennis E. Breedlove, Robert Bye, Annetta Carter, Lauramay T. Dempster, Noel H. Holmgren, and Reid Moran, who kindly collected cytological material for this investigation. We also express our sincere appreciation to Lincoln Constance and Paul Silva for critical reading of the manuscript and helpful suggestions, to Fei Mei Chuang for skillful technical assistance, and to Guy L. Nesom for a loan of 21 specimens of Mexican Castilleja (TX). 2 Department of Biological Sciences, Illinois State University, Normal, Illinois 61761, U.S.A. 3Jepson Herbarium, University of California, Berkeley, California 94720, U.S.A. ANN. MISSOURI BOT. GARD. 80: 974-986. 1993. This content downloaded from 157.55.39.211 on Mon, 08 Aug 2016 04:45:56 UTC All use subject to http://about.jstor.org/terms Volume 80, Number 4 Chuang & Heckard 975 1993 Chromosome Numbers of Neotropical Castilleja 1968; Heckard & Chuang, 1977; Chuang & Heckard, 1982; Chuang & Heckard, unpublished data) has shown that more than half of the 100 species counted are polyploid or have a diploid level plus one or more polyploid levels. For example, one species complex, Castilleja affinis-litoralis, has a diploid plus five levels of polyploidy from 4x to 12x. widespread C. miniata of the western United States and Canada has a diploid and four additional levels of polyploidy from 4x to

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