CYTOGENETICS OF LATHYRUS-PALUSTRIS, NATURAL AUTOHEXAPLOID

American as well as British forms of the perennial plant Lathyrus palu stris have 2n = 42 chromosomes with one group of 6 long submetacentric chromosomes, two groups of 6 medium-long subacrocentric chromosomes, three groups of 6 medium-long to medium-short submetacentric to subacr ocentric chromosomes, and one group of 6 medium-short metacentric chro mosomes. One haploid complement measures 45.8 mu m at somatic metaphas e. At meiotic first metaphase both forms show extensive multivalent fo rmation. In 50 metaphase I cells of one plant of the British form ther e were 51 ring hexavalents, 80 chain and open-branched hexavalents of various forms, 2 quinquivalents, 41 ring quadrivalents, 58 chain quadr ivalents, 20 branched quadrivalents of various forms, 1 trivalent, 128 ring bivalents, 280 open bivalents, and 9 univalents. It is concluded that L. palustris is most likely a natural autohexaploid with frequen t multivalent pairing, many points of pairing initiation, several part ner exchanges per multivalent, and many interstitial chiasmata. it may well be the first fully documented true natural autohexaploid reporte d. Pollen fertility was 56.2% and seed set 37%, apparently sufficient for a perennial plant species.