Karyotype characterisation of Brazilian species of the genus Psychotria L. — subfamily Rubioideae (Rubiaceae)

Abstract

The pantropical genus Psychotria L., probably the largest among angiosperms, occurs in different Brazilian vegetal formations. This work determined the chromosome numbers and karyotypic characteristics of ten species of Brazilian Psychotria. The chromosome numbers ranged from 2n = 22, in five species (P. hoffmannseggiana (Willd. ex Roem. & Schult.) Mull. Arg., P. lupulina Benth., P. marginata Sw., P. tenerior (Cham.) Mull. Arg., and P. trichophora Mull. Arg.), to 2n = 40, in P. mapourioides DC., and 2n = 44 in four other species (P. carthagenensis Jacq., P. gracilenta Mull. Arg., P. longipes Mull. Arg. and P. suterella Mull. Arg.). In addition to these differences, great variations in chromosome lengths and karyotypic formulae were also observed among these species. Chromosome length varied from 5.59 μm to 0.90 μm and no relationship was detected between chromosome numbers and lengths in any species. Chromosomes are principally metacentric, except for P. mapourioides that presents mainly submetacentric chromosomes. Karyotypic asymmetry rate (TF%) ranged from moderate (TF% = 38.83) to highly symmetric (TF% = 50.00). The difference in chromosome numbers of Psychotria carthagenensis (2n = 44) and P. mapourioides (2n = 40) is very important to taxonomists, because these have great difficulty in identifying and differentiating these two species with the sole use of morphological characteristics, since some individuals have intermediate characteristics between both species. Although this study does not allow for a consistent cytotaxonomic analysis, not even to delimit P. subgen. Psychotria and P. subgen. Heteropsychotria, this karyotype analysis of some Brazilian species, along with their morphology, may contribute to a better knowledge of the genus.