title: Chromosome  number variation and evolution in Neotropical Leguminoseae (Mimosoideae) from  northeastern Brazil.
abstract: Most members of the subfamily Mimosoideae have pantropical distributions, variable habits, and a basic chromosome number x = 13. We examined karyotypic evolution of 27 species of this subfamily occurring principally in northeastern Brazil by examining chromosomes stained with Giemsa. All of the species had semi-reticulated interphase nuclei and early condensing segments in the proximal region of both chromosome arms. The basic number x = 13 was the most frequent, with 2n = 2x = 26 in 19 of the species, followed by 2n = 4x = 52 and 2n = 6x = 78. However, the three species of the genus Calliandra had the basic number x = 8, with 2n = 2x = 16, while Mimosa cordistipula had 2n = 4x = 32. The karyotypes were relatively symmetrical, although bimodality was accentuated in some species, some with one or two acrocentric pairs. As a whole, our data support earlier hypotheses that the Mimosoideae subfamily has a basic number of x = 13 and underwent karyotypic evolution by polyploidy. However, x = 13 seems to be a secondary basic number that originated from an ancestral stock with x₁ = 7, in which polyploidy followed by descending disploidy gave rise to the current lineages with x = 13. Another lineage, including current representatives of Calliandra with x = 8, may have arisen by ascending disploidy directly from an ancestral monoploid stock with x₁ = 7.
authors: Programa de Pós-Graduação em Agronomia, Departamento de Ciências Biológicas, Universidade Federal da Paraíba, Areia, PB, Brasil.
authors: E C X R
authors: EC
authors: Santos
authors: R
authors: R
authors: Carvalho
authors: E M
authors: EM
authors: Almeida
authors: L P
authors: LP
authors: Felix
mesh_terms: D001938:Brazil; D002467:Cell Nucleus / Q000235:genetics; D032461:Chromosomes, Plant / Q000235:genetics*; D019143:Evolution, Molecular; D007887:Fabaceae / Q000235:genetics*; D014644:Genetic Variation; D007399:Interphase / Q000235:genetics; D013045:Species Specificity; D014329:Tropical Climate