Resumen de Karyological studies in Iberian Sonchus (Asteraceae: Lactuceae): S. oleraceus, S. microcephalus and S. asper and a general discussion
José Antonio Mejías Gimeno, Cristina Andrés Camacho
Chromosome numbers and karyotypes ofSonchus oleraceus (n-16, 2n-32), S. asper (n=9, 2n = 18 for subsp, asper and subsp, glaucescens, and S. microcephalus (n-15, 2n-30) are studied; for the first time their idiograms are given. Karyotypes mainly comprise small chromosomes with a degree of asymmetry 2B in S. oleraceus and S. microcephalus and 2A or 2A-2B in S. asper. No karyological differences can be pointed out between S. asper subspecies. Data presented support the amphiploid character ofS. oleraceus, and the origin of S. microcephalus through a dysploid process involving the former taxon. In Iberian representatives of the genus, diagrams ofkaryotype asymmetry indices show a cluster grouping for species, with the detached exceptions of S. maritimus and S. crassifolius, which spontaneously hybridize in central Spain.
A review of available karyological data shows that in the evolution of the genus Sonchus s.1. and relatives, the basic chromosome number x=9 has generally been maintained. Dysploidy is restricted to the series S. bourgeaui (n=8) - S. tenerrimus (n=7) and S. oleraceus (n=16) - S. microcephalus (n=15), evolutionarily related and included in the present subgenus Sonchus. Polyploidy has been detected in a total of nine taxa of Sonchus and in the genera Embergeria, Kirkianella, and Dendroseris, being more common in peripheral regions of the distribution area of the group. Five diversification centers are proposed for the whole group, of which the Western Mediterranean area, including the Iberian Peninsula, is related to diversification of the present subgenus Sonchus
