Karyomorphology and karyotype asymmetry in the South American Caesalpinia species (Leguminosae and Caesalpinioideae).

With the purpose of addressing the pattern of karyotype evolution in Caesalpinia species, chromosome morphology was characterized in five species from Brazil, and karyotypic asymmetry was analyzed in 14 species from South America. All accessions had the chromosome number 2n = 24, which was first described here for Caesalpinia laxiflora Tul. and Cenostigma macrophyllum Tul. The karyotype formula of C. laxiflora, Caesalpinia pyramidalis Tul., and C. macrophyllum was 12 m. The formula varies amongst the populations of Caesalpinia bracteosa Tul. (11 m + 1 sm) and Caesalpinia echinata Lam. (10 m + 2 sm and 9 m + 3 sm). The intra- and interspecific variations in chromosome length were significant (analysis of variance, P < 0.05). Analyzing the asymmetry index (AI), revealed that Caesalpinia calycina Benth. had the most asymmetrical karyotype (AI = 10.52), whereas Caesalpinia paraguarienses (D. Parodi) Burkat. and Caesalpinia gilliesii (Hook.) Benth. had the most symmetrical karyotypes (AI = 0.91 and 1.10, respectively). There has been a trend to lower AI values for the Caesalpinia s.l. species assigned in Libidibia and intermediate values for those combined into Poincianella. On the other hand, the karyotypes of Erythrostemon species had extremely different AI values. This study confirms the existence of karyotype variability in Caesalpinia s.l. while revealing a possible uniformity of this trait in some of the new genera that are being divided from Caesalpinia s.l. More broadly, the 2n = 24 chromosome number is conserved. Metacentric chromosomes and low AI values predominate among Caesalpinia s.l. and Cenostigma.