MORPHOLOGICAL AND CYTOLOGICAL VARIATION IN HELIANTHUS PETIOLARIS WITH NOTES ON RELATED SPECIES

Helianthus petiolaris Nutt. is an annual sunflower of wide distribution in sandy areas of the central and western United States. Most taxonomists have recognized two taxa within the species, H. petiolaris proper, and H. petiolaris var. canescens A. Gray, although some have considered the latter a distinct species, H. canus (Britton) Wooton and Standley, and it is so treated here. The present author (Heiser, 1958) recognized two subspecies, H. petiolaris ssp. petiolaris and H. petiolaris ssp. fallax, in what previously had been treated as the typical element. In the present paper, the morphological variation and geographical distribution of H. petiolaris, the cytogenetic analyses of hybrids within the species, and the results of hybridization with other annual species are considered. Geographical distribution. -The map (fig. 1) has been compiled from the herbarium specimens from Gray Herbarium, Indiana University, Inter-Mountain Herbarium, Missouri Botanical Garden, United States National Herbarium, and the University of Wisconsin. It can be seen that H. petiolaris ssp. petiolaris has its greatest concentration in the southern Great Plains,2 which probably represents its pre-human range. It is now also fairly well established in the Central Plains. In Indiana, where excellent records are available (Deam, 1940), its spread since 1900 has been observed. In the East it occurs as an adventive weed and it is now well established in some areas in the Southeast. There is a discontinuity in the western part of the range, and it is again found in three areas in California. Helianthus petiolaris ssp. fallax is limited to more arid regions and is found only in western Colorado, eastern and southern Utah, New Mexico, and Arizona. The two subspecies intergrade to some extent on the Colorado-New Mexico and New Mexico-Texas borders, and it is not always possible to assign subspecific names to herbarium specimens from these areas. Helianthus canus ranges from West Texas to California (area shown in outline on map). The distribution of the recently described H. neglectus Heiser, a close relative of H. petiolaris, limited to a small area of West Texas, is indicated on the map. Hybrids between H. annuus L. and H. petiolaris for which there are herbarium vouchers are also plotted. Helianthus annuus has an even wider distribution than H. petiolaris, and although the two species have distinct soil preferences they are frequently found growing adjacent to each other. Morphological Variation.-Some idea of the regional variation can be gained from figure 2, in which seven characters have been used to construct polygons for each of the populations grown in the field at Bloomington in 1957 or 1958. The mean values for number of phyllaries, "phyllary index," "leaf index," number of rays, and the percentage of plants showing the absence of leafy bracts, presence of purple anthers, and absence of long trichomes on the peduncles are represented. The number of plants grown in each population and ' This study was carried out with the aid of grants from the National Science Foundation. I should also like to express my thanks to Dr. R. E. Cleland and Dr. G. L. Stebbins, Jr. for reading portions of the manuscript, to the numerous individuals (see table 1) who supplied seeds, and to the students who helped with various phases of the investigation. Grateful acknowledgment is also made to the curators of the herbaria who have made material available for study. 2 It is also recorded from Oregon and Idaho but exact localities could not be ascertained.