Here we describe the morphological variability, chromosome number, and chromosome size in Mimosa diversipila. This species comprises two varieties, which are distinguished by the indumentum. However, this character is insufficient for circumscription of these infraspecific taxa. Using multivariate techniques, we found that quantitative characters were useful for identification of the varieties, which also have a different geographic distribution. Cytogenetic studies revealed that these taxa form a polyploid complex and that the polyploidy may contribute to the morphological variability observed.