The monotypic genus Zigadenus occupies a critical position in the evolution of Melanthieae as sister to the clade comprising the rest of the genera in the tribe. Meiotic (n = 27) and mitotic (2n = 54) chromosome counts for Zigadenus glaberrimus documented here do not support a long-standing tentative report of 2n = 52. The likely base chromosome number of the tribe and significance of chromosome numbers as generic synapomorphies are discussed in reference to these newly recorded counts for Zigadenus glaberrimus, a likelyhexaploid.