Cyto-Taxonomic Studies in Oryzopsis

Abstract

Cytological and morphological studies in Oryzopsis indicate that the section Pipta-therum (of which 3 spp. examined had 271 = 24 chromo-somes) and the genus Stipa in part represent divergent lines of specialization on a common primary basic number of ar=6 chromosomes, and that these lines have reticulated to form the polyploid section Eriocoma with 2n= 48 chromosomes. The section Euoryzopsis (of which 3 species examined had 2n = 22 chromosomes) represents mainly the diploid spp. of a line tentatively isolated from the x = 12 (or 6) lines by a change to a secondary basic number of x: =11. The latter line in turn has reticulated with the Piptatherum line to form 2 allopolyploid spp. of Oryzopsis with 2n = 46 chromosomes. It is suggested that the secondary basic number of x = ll may have originated thru a change from 2n=12 to 2n=10 within the Stipa line, with subsequent allopolyploidy between 2n = l0 individuals and the original 2n=12 lines in both Stipa and Piptatherum. 7 new somatic chromosome counts are reported: Oryzopsis holciformis, 24; O. micrantha, 22; O. pungens. 22; O. kingii, 22; 0. asperifolia, 46; O. racemosa, 46; Stipa webberi, 32.