Chromosomal studies on Neotropical Limnocharitaceae (Alismatales)

The family Limnocharitaceae comprises three genera of herbaceous aquatic plants: Limnocharis and Hydrocleys, naturally found in Neotropical regions, and Butomopsis, found in Paleotropical regions. In order to analyze the karyotypic characteristics of the Neotropical genera, root tips of L. flava, L laforestii and H. nymphoides were cytologically prepared. The average karyotypes were constructed based on 10 metaphasic cells for each species. The chromosome numbers found were 2n = 20 for L. flava and L. laforestii and 2n = 16 for H. nymphoides. In all species, the chromosome length varied gradually and the highest quantity of chromatinic material was found in H. nymphoides (total chromatin length, TCL = 58.6 mum), as compared with L. flava and L. laforestii (TCL = 51.0 and 41.9 mum, respectively). About 75% of the chromosomes were acrocentric and all three species presented asymmetric karyotypes, with TF% rates equal to 17.8% (L. flava), 15.3% (L. laforestii) and 19.7% (H. nymphoides). Taking karyotypic asymmetry as a derivative character, it is concluded that, in the family Limnocharitaceae, the derivation may have been accompanied by an increase in reproductive elements (mainly carpels) and chromosome number. Chromosome fragmentation would have led to both higher chromosome numbers and karyotypic asymmetry. (C) 2002 Elsevier Science B.V. All rights reserved.