MOLECULAR PHYLOGENETICS OF THLASPI SL (BRASSICACEAE) BASED ON CHLOROPLAST DNA RESTRICTION SITE VARIATION AND SEQUENCES OF THE INTERNAL TRANSCRIBED SPACERS OF NUCLEAR RIBOSOMAL DNA

Systematics of the genus Thlaspi s.l. is difficult and controversial. Previous hypotheses have been based on morphological and anatomical da ta. We have analyzed sequence variation of the internal transcribed sp acer (ITS) regions of nuclear ribosomal DNA (nrDNA) among 13 Thlaspi s .l. taxa, representing all sections of the genus. Phylogenetic relatio nships among ITS sequences of the Thlaspi s.l. taxa studied are in gen eral concordance with a previously published chloroplast DNA based phy logeny of this group. Most-parsimonious trees from ITS and chloroplast DNA data support three groups that are congruent with lineages (Thlas pi s.str., Noccaea-Raparia, Microthlaspi) previously described by Meye r on the basis of seed anatomy. The ITS data grouped Microthlaspi gran atense outside the Microthlaspi clade and, therefore, Microthlaspi app eared paraphyletic on the ITS tree, in contrast with the chloroplast D NA phylogeny. We speculate that concerted evolutionary forces have act ed among different nrDNA arrays (brought together in M. granatense by hybridization with a related taxon), resulting in the fixation of the alien species nrDNA type in M. granatense, which, however, maintains a Microthlaspi chloroplast genome type. Both molecular data sets detect ed intraspecific variation among Microthlaspi perfoliatum accessions o f different geographic origin and different ploidy levels. Our molecul ar evidence would suggest the hybrid origin of polyploid M. perfoliatu m from diploid M. perfoliatum and M. natolicum.