Chromosomes of four species of Commelina (Commelinaceae)

Abstract

Chromosome numbers, meiotic behaviour and karyotypes in 27 populations belonging to four species of Commelina L. from north-east Argentina and Paraguay have been studied. The basic number of chromosomes in all accessions is x = 15. For C. platyphylla Klotzsch ex Seub. (2n = 2x = 30) the chromosome number is reported for the first time. A new ploidy level (2n = 6x = 90) is presented for South American accessions of C. diffusa Burm. f. Commelina erecta L. and C. obliqua Vahl are tetraploids (2n = 4x = 60). Chromosomes behave regularly at meiosis and pair as bivalents in diploid and polyploid accessions. Chiasma frequency and distribution is reported for each species. The karyotype descriptions of C. platyphylla (18m + 12sm), C. obliqua (30m + 26sm + 4st) and hexaploid C. diffusa (38m + 44sm + 8st) are reported here for the first time. The data suggest an allopolyploid condition for tetraploids of C. erecta and C. obliqua. © 2005 The Linnean Society of London.