MONOPHYLY OF ANEUPLOID ASTRAGALUS (FABACEAE) - EVIDENCE FROM NUCLEAR RIBOSOMAL DNA INTERNAL TRANSCRIBED SPACER SEQUENCES

Evolutionary relationships within Astragalus L. (Fabaceae) were inferr ed from nucleotide sequence variation in nuclear ribosomal DNA of both New World and Old World species. The internal transcribed spacer regi ons (ITS) of 18S-26S nuclear ribosomal DNA from representatives of 26 species of Astragalus, three species of Oxytropis DC., and two outgrou p taxa were analyzed by polymerase chain reaction amplification and di rect DNA sequencing. The length of the ITS 1 region within these taxa varied from 221 to 231 bp, while ITS 2 varied in length from 207 to 21 7 bp. Of the aligned, unambiguous positions, approximately 34% were va riable in each spacer region. In pairwise comparisons among Astragalus species and outgroup taxa, sequence divergence at these sites ranged from 0 to 18.8% in ITS 1 and from 0 to 21.7% in ITS 2. Parsimony analy ses of these sequences resulted in a well-resolved phylogeny that is h ighly concordant with previous cytogenetic and chloroplast DNA evidenc e for a major phylogenetic division in the genus. These data suggest t hat the New World aneuploid species of Astragalus form a monophyletic but morphologically cryptic group derived from euploid species of Old World (Eurasian) origin, which are consequently paraphyletic.