Citotaxonomia do gênero neotropical Epidendrum L.(Laeliinae, Orchidaceae):

Abstract

Epidendrum L. (Laeliinae, Orchidaceae) has about 1,800 species distributed in the Neotropical regions. Their species present a high degree of morphological variation, ecological interactions and diversity in the chromosome number, which, at times, makes it difficult to establish infrageneric classifications and taxonomic organization in the genus. The aim of this research was to discuss the chromosomal number and the distribution of heterochromatic regions with the use of the fluorochromes cromomycin A3 (CMA) and 4'6-diaminidine-2-phenylindole (DAPI) in species of different infrageneric groups of Epidendrum, as well as to analyze the karyotype (chromosome number and heterochromatic bands) and genome size (2C-value) in species of the "Difforme" and "Nocturnum" groups. The "Nocturnum" group is marked by polyploidy and regions rich in CMA+ bands located in the pericentromeric region. DNA content was generally correlated to the level of ploidy, where one diploid species presented 2C = 2.91 ρg, tetraploids species presented 2C ~ 6.00 ρg and one hexaploid species presented 2C = 8.92 ρg. For the "Difforme" group, all species presented 2n = 40 and variable numbers of terminal (0-4) and pericentromeric (8-16) CMA+/DAPI– bands. DNA content ranged from 3.99 ρg in E. campaccii Hágsater & L. Sanchez to 5.68 ρg in E. althausenii A.D. Hawkes. The data of heterochromatin distribution, 2C-value, chromosome number and morphological characters allowed discussing new taxonomic considerations for the species of the "Difforme" and "Nocturnum” groups. The discussion involving heterochromatin distribution on infragenerics groups of Epidendrum comprised 47 species belonging to 20 groups. New chromosome records are recorded for 22 species. Most karyotypes presented 2n = 40 and heterochromatic regions rich in GC (CMA+). Heterocromatic bands rich in AT (DAPI+) were recorded especially in the Schistochilum and Loefgrenii groups. Variations in the chromosomal number allied to the heterochromatin distribution appear to follow a specific pattern for most of the groups analyzed. Ecological factors such as habit and habitat and geographic distribution are also discussed among the different groups of Epidendrum and reconciled in the infrageneric discussions for the genus.