Chromosome studies in Argentinian species of Stemodia L. (Scrophulariaceae)

SOSA, MARÍA DE LAS MERCEDES & GUILLERMO SEIJO; GUILLERMO SEIJO

CYTOLOGIA

The Japan Mendel Society

Lugar: Tokio; Año: 2002 vol. 67 p. 261 - 266

0011-4545

Chromosome numbers for 56 populations belongingof eight South American species of Stemodia were determined. The numbers 2n = 22 found in S. hassleriana and S. palustris, and 2n = 44 in S. lobelioides are the first records for the species, while those found in S. hyptoides (2n = 22 and 2n = 44) and S. stricta (2n = 22) constitute new cytotypes for each taxa. Chromosome analysis in different populations also confirmed the numbers previously found for other species of Stemodia. The basic chromosome number x = 11 was confirmed for New World species. Chromosome numbers indicate the existence of a polyploid series in S. hyptoides with 2n = 22, 44, 66. Moreover, the existence of at least different ploidy levels, both within and among species, evidences that polyploidy has been one of the mechanisms involved in the evolution of the genus. The geographical distribution of different species are analyzed and discussed in the light of their extant morphological variation and taxonomic implications.