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.

We investigated four orchids of the genus Maxillaria (M. discolor, M. acicularis, M. notylioglossa and M. desvauxiana) in regard to the position of heterochromatin blocks as revealed using chromomycin A3 (CMA) and 4'-6-diamidino-2-phenylindole (DAPI) fluorochrome staining and 5S and 45S rDNA sites using fluorescence in situ hybridization (FISH). The species showed differences in chromosome number and a diversified pattern of CMA+ and DAPI+ bands, including heteromorphism for CMA+ bands. The 5S and 45S rDNA sites also varied in number and most of them were co-localized with CMA+ bands. The relationship between 5S rDNA sites and CMA+ bands was more evident in M. notylioglossa, in which the brighter CMA+ bands were associated with large 5S rDNA sites. However, not all 5S and 45S rDNA sites were co-localized with CMA+ bands, probably due to technical constraints. We compare these results to banding data from other species and suggest that not all blocks of tandemly repetitive sequences, such as 5S rDNA sites, can be observed as heterochromatin blocks

Because of their fragmented nature, inselberg species are interesting biological models for studying the genetic consequences of disjoint populations. Inselbergs are commonly compared with oceanic islands, as most of them display a marked ecological isolation from the surrounding area. The isolation of these rock outcrops is reflected in the high number of recorded endemic species and the strong floristic differences between individual inselbergs and adjacent habitats. We examined the genetic connectivity of orchids Epidendrum cinnabarinum and E. secundum adapted to Neotropical inselbergs of northeastern Brazil. Our goals were to identify major genetic divergences or disjunctions across the range of the species and to investigate potential demographic and evolutionary mechanisms leading to lineage divergence in Neotropical mountain ecosystems.

The Cymbidioid phylad presents the widest chromosome number variation among orchids, with records varying from 2n = 10 in Psygmorchis pusilla to 2n = 168 in two species of Oncidium. In the present work, a total of 44 species were studied belonging to 20 Cymbidioid genera, as a contribution to clarifying the karyological evolution of the group. All the plants investigated were collected in Brazil, mainly in the northeast region. The chromosome variation found was similar to that previously registered in the literature. Chromosome numbers observed were: 2n = 54 (subtribe Eulophiinae), 2n = 44, 46, 92 (subtribe Cyrtopodiinae), 2n = 54, ca. 108 (subtribe Catasetinae), 2n = 52, ca. 96 (subtribe Zygopetalinae), 2n = 40, 80 (subtribe Lycastinae), 2n = 40, 42 (subtribe Maxillariinae), 2n = 40 (subtribe Stanhopeinae), 2n = 56 (subtribe Ornithocephalinae), and 2n = 12, 20, 30, 36, 42, 44, 56, 112, ca. 168 (subtribe Oncidiinae). Interphase nuclei varied widely from simple chromocenter to complex chromocenter types, with no apparent cytotaxonomic value. In the genera Catasetum and Oncidium, the terrestrial and lithophytic species presented higher ploidy levels than the epiphytic species, suggesting a higher adaptability of the polyploids to those habitats. The primary base number x = 7 seems to be associated to the haploid chromosome numbers of most Cymbidioid groups, although n = 7 was observed only in two extant genera of Oncidiinae. For each tribe, subtribe and genus the probable base numbers were discussed along with the possible relationships to the primary base number x1 = 7 admitted for the whole phylad.

A contaminação biológica é uma das principais causas da perda de biodiversidade atualmente no planeta. Este trabalho teve como objetivo avaliar os impactos causados pela invasão biológica de Prosopis juliflora sobre a composição e a estrutura do componente arbustivo-arbóreo da caatinga, tanto no estrato adulto quanto na regeneração natural. Foram plotadas 20 parcelas de 400 m², sendo 10 em um remanescente de caatinga bem conservada (Ambiente I) e 10 em uma área de caatinga invadida por P. juliflora (Ambiente II). A área invadida apresentou-se muito mais pobre em relação à primeira, em todos os parâmetros avaliados. Os impactos causados pela invasora foram sentidos tanto na estrutura, quanto na diversidade biológica da comunidade. A Densidade Relativa de P. juliflora no estrato adulto da área invadida atingiu cerca de 90%, o que reflete a sua capacidade de competição e eliminação das demais espécies. O índice de diversidade de Shannon-Weaver (H') apresentou os valores de 2,81 e 0,61 para o componente adulto dos Ambientes I e II, respectivamente. Para a regeneração natural os valores desse índice foram de 2,31 e 1,14 para os mesmos Ambientes. Conclui-se que P. juliflora forma densos maciços populacionais e compete com as espécies nativas, afetando severamente a composição florística, a diversidade e a estrutura das comunidades autóctones invadidas.