Bulnesia

Abstract: A study of nuclear DNA content was made in telophase nuclei (2C) of the root apex of germinating seed in nine populations of the following species and cytotypes of Larrea: L. nitida (2x), L. divaricata (2x), L. cuneifolia (4x) and L. tridentata (2x, 4x, 6x). There were no significant differences in DNA content per basic monoploid genome among the diploid taxa nor between the latter and the tetraploid, among tetraploids or between tetraploids and the hexaploid. On the other hand, the difference between means was significant when all diploids were compared with the hexaploid cytotype. These results would indicate: (1) Speciation at the diploid level in Larrea has not produced great differences in DNA content per basic genome. This is in contrast with the related genus Bulnesia. (2) In Larrea there is a slight diminution in DNA content per basic genome when there is an increase in ploidy level. (3) Species of Larrea, Bulnesia and Pintoa (Zygophyllaceae) that inhabit the most arid environments are the ones possessing the highest DNA content. (4) This increase is due to an increment in ploidy level in Larrea and an augment of intrachromosomal DNA in Bulnesia and Pintoa.