Eighty-eight chromosome number counts representing 62 species in nine genera of the Lythraceae are presented based primarily on meiotic figures from pollen mother cells. Included are first reports for 47 species and the first count for the monotypic genus Koehneria. Numbers for 40 species of Cuphea from Brazil and Bolivia are reported, significantly increasing representation of chromosome number data for South American sections of the genus. Comparisons of the new counts are made to previously published numbers for each genus. Basic numbers for 24 of the 31 genera are provided. Eight genera retain the apparent original diploid number of x = 8; 12 are functional diploids of paleopolyploid origin with secondary basic numbers of x = 15, 16, 24, 28, or 32. Polyploid events are hypothesized to have occurred early in the evolution of the family so that the majority of monotypic or ditypic genera, which today constitute 65% of the family, are relictual polyploids. The most chromosomally diverse and actively speciating genera are the herbaceous perennials Ammannia, Nesaea, Cuphea, and Lythrum. In contrast, the woody genera Diplusodon, Ginoria, and Lafoensia, are species-rich but speciation has not involved chromosome number changes. Further understanding of chromosomal evolution in Lythraceae will depend on production of well-supported phylogenies for the family and cytological investigations in the genera where many different chromosome numbers occur.

Communicating Editor: John V. Freudenstein