Karyotype analysis in Argentinean species of Caesalpinia (Leguminosae)

Abstract

Somatic chromosomes of three Caesalpinia L. species (subfam. Caesalpinioideae, tribe Caesalpinieae: C. gilliesii, C. mimosifolia — both endemic to Argentina —, and C. paraguariensis, endemic to the Chaco region) were studied, being this the first chromosomic report for all of them. These species were diploid (2n = 24) and showed a variable percentage of tetraploid cells. Chromosomes were small: the average chromosome length was 1.90 ± 0.17 μm. The haploid karyotype length was relatively homogeneous (range: 20.67–24.74 μm, mean: 22.89 ± 2.06). Although Caesalpinia species were morphologically different, their differentiation was not followed by chromosomal variations. Effectively, all showed the same chromosome number and symmetrical haploid karyotype formula: 8 m + 4 sm. Microsatellites were present in chromosome pair no. 2 and were attached to the short arms. A cluster analysis based on karyotype features showed that C. gilliesii and C. paraguariensis were closer and that C. mimosifolia is more different because it has the shortest mean chromosome length and the highest mean arm ratio and A2 values. Karyo-typic features obtained suggest that no major visible chromosomal rearrangements have occurred during the differentiation in the group, although cryptic structural changes, as paracentric inversions or reciprocal translocations of segments of similar length, may have taken place.