A CYTOTAXONOMIC STUDY IN THE GENUS ANDROPOGON

Abstract

TIHE SECTION AMPHILOPHIS of the genus Andropogon is represented in North America by plants referred to the species A. sacchiaroides Swartz, A. barbinodis Lag., A. exaristatus (Nash) Hitchc., A. edwardsianus Gould, A. perforatus Trin ex Fourn., and A. wrightii Hack. All are perennial bunchgrasses with paniculate inflorescences of few to many racemose flowering branches in a terminal cluster. This study was made primarily to establish a more satisfactory basis for taxonomic disposition of these grasses. The cytological and morphological data will serve as the foundation for a comprehensive investigation of systematic relationships in the Amphilophis section. The writer is indebted to Dr. Edgar Anderson of the Missouri Botanical Garden and to Dr. G. Ledyard Stebbins, Jr., of the University of California, for numerous suggestions. Dr. Charles LaMotte of the Agricultural and Mechanical College of Texas has generously contributed time and effort in the preparation of the photomicrographs. Grateful acknowledgment for the loan of herbarium specimens is made to the curators of the herbaria of the University of Arizona, the University of California, the University of Texas, Southern Methodist University, and the U. S. National Museum. Morphological data were obtained from herbarium specimens and from population samples consisting of ten randomly selected influorescences. The latter for the most part were taken from plants growing in their natural habitats. Samples of the two species designated as taxon RF 70.and taxon RF 402, and one collection of A. exaristatus were obtained from plants grown in the Range and Forestry Department grass nursery at the A. and M. College of Texas. No population samples or chromosome counts were obtained for A. wrightii and this species is known to the writer only by herbarium specimens. Cytological studies were made of pollen mother cell divisions. Bud material was obtained mainly from plants growing in their natural habitat, but some chromosome counts were made from plants grown from seed and a few were obtained from transplanted clones. Grasses of the Amphilophis section of Andropogon flower whenever moisture and temperature conditions are favorable for growth. In Texas and adjacent areas the flowering period extends from spring to late fall, a highly desirable situation from the viewpoint of the cytologist. Bud material for P.M.C. counts was fixed in a solution of 3:1:1 absolute alcohol, glacial acetic acid, and chloroform. For storage the buds were transferred to 70 per cent alcohol and kept in re-