Chromosomal studies in Acmella bellidioides (Sm.) R.K.Jansen (Asteraceae) from northeast Argentina

Abstract

Acmella bellidioides is a perennial small herb that naturally grows in north-east Argentina, Brazil, Paraguay and Uruguay. The species belongs to section Megaglottis and it has a chromosome number of n = 13. It exhibits a wide range of morphological variation that has created diffi cult in distinguishing it from closely related species of this section. Acmella bellidioides was collected in open fi elds with sandy and stony soils. Classical cytogenetic techniques were applied to analyze chromosomes at mitosis, examine behavior during microsporogenesis, and determine its karyotype. Acmella bellidioides is diploid with 2n = 2x = 26 small size chromosomes (2.22 - 4.01 ?m) and 39.25 ?m/genome. Its karyotype, 12m + 10sm + 4st is unimodal (A2 = 0.16 / R = 1.80) and slightly asymmetrical (A1 = 0.42 / i = 35.88 / r>2 = 0.54 / AI = 3.69) (3A Stebbins category). Chromosome pair No. 9 (sm) has a terminal macrosatellite in the short arm. Microsporogenesis is normal and produces viable pollen grains (>90%). Meiotic behavior is regular. In PMC at diakinesis and metaphase I, 13 bivalents were observed. This is the fi rst karyotypic study in Acmella. Our record of 2n = 2x = 26 chromosomes agrees with the basic number x = 13 proposed for the genus and for section Megaglottis, regarded as most ancestral. This might be regarded, therefore, as the basic karyotypic description for Acmella.