Cromosomas en vernonia platensis y especies afines (asteraceae)

Abstract

El género Vernonia Schreb. presenta una gran diversidad de números cromosómicos, habiéndose reportado especies con x=7, 9, lO, 11,12,14,15,16, 17 Y 19 (Dematteis, 1996). En el viejo mundo los números básicos más frecuentes son x=9 y x=10, mientras que en el continente americano los más comunes son x=17 y x=16. El número base x=10 se ha citado en el nuevo mundo solamente para un pequeño grupo de especies que constituyen la subsección Flexuosae (Cabrera, 1944) o serie Flexuosae (Jones, 1981). El conocimiento citológico de este grupo reviste particular interés, debido a que x=10 es un número básico relativamente primitivo en el género Gones, 1979).The somatic chromosomes of Vernonia platensis and three others closely related species were analyzed. Al! these species belong to the subsection or series Flexuosae, which is the only American group with the primitive basic chromosome number x=10. In this paper two new cytotypes for V. platensis are reported and the karyotypes of V. verbascifolia and of four cytotypes of V. platensis are presented for the first time. The results of the chromosome analysis were the following: V. flexuosa, 2n=40 (28m + 12sm); V. lepidifera, 2n=20 (8m + 2m-sm + 10sm), V. platensis, 2n=20 (10m + 2m-sm + 8sm), 2n=40, 2n=60, 2n=80 and V. verbascifolia, 2n=20 (8m + 4m-sm + 8sm). The 4x, 6x and 8x cytotypes of V. platensis present the same karyotype that the diploid suggesting an autoploid origino The karyotypes of the species here reported differ principally in total length, asymmetry and number of metacentrics and submetacentrics. They show also variation in number, form and location of the satellites. The results are discussed in relation to the taxonomic position of the species and to previous chromosome studies in the group.