Autotetraploidy and chromosome number in a cultivar of Panicum maximum Jacq. (Gramineae / Poaceae). The objective of this research was to evaluate cytological behavior with special emphasis on ploidy level of P. maximum cv. Tanzania, cultivated in Brazil, which corresponds to a wild ecotype of African origin. For cytological analysis inflorescences were fixed in 3:1 etilic alcohol: acetic acid solution for 24 hours and stored in 70% alcohol at low temperature. The usual procedures for meiosis studies were followed for slide preparation, with staining by 1% propionic carmine. For each slide, three flowers were taken of distinct points within tassel. A minimum of 200 cells per plant were observed. Meiotic abnormalities occurred in 20% of analyzed pollen mother cells. All evaluated plants showed 36 chromosomes in diakinesis. Among 109 diakinesis where chromosomes were counted and chromosome associations analyzed, 99 presented multivalent especially tetravalent, which indicates autotetraploid origin, where 2n=4x=36.