Karyotype differentiation in Ameroglossum (Linderniaceae) and closely related genera endemic to Brazilian inselbergs

Abstract

Ameroglossum is composed of shrubs endemic to inselbergs in north-eastern Brazil, currently circumscribed in Linderniaceae. Chromosomal counts for this family are few, but quite variable, ranging from 2n = 14 to 60. We investigated the chromosomal numbers of 14 species of Linderniaceae with emphasis on Ameroglossum and analysed the distribution of heterochromatin and 5S and 35S rDNA sites for most species. We found 2n = 60 for the species of Ameroglossum (except Ameroglossum genaroanum with 2n = 64), Catimbaua and Isabelcristinia, 2n = 50 for Cubitanthus alatus and 2n = 28 for Torenia thouarsii and Vandellia diffusa. All of them had small, similar chromosomes and 5S and 35S rDNA sites overlapping with CMA+ bands. The species with 2n = 50-64 showed a single pair of 5S and 35S rDNA sites, V. diffusa had two pairs of 5S and one pair of 35S rDNA sites and T. thouarsii had two pairs of each. Furthermore, other CMA+ and DAPI+ bands have been seen in almost all species. The karyotypical similarities among the species of Ameroglossum, Catimbaua, Cubitanthus and Isabelcristinia suggest a close relationship between representatives of Linderniaceae typical of inselbergs.