The first systematic revision of the subtropical grass genus Sorghastrum is proposed. Detailed morphological and anatomical descriptions are shown. The number of species assigned to this genus has been quite changeable (from 10 to 20 species have been proposed). Sorghastrum comprises 17 accepted species, occurring mainly in the New World. However, two species are established in Africa. The altitudinal range of this genus is wide, from sea level to more or less 3000 m. In relation with its altitudinal variability, Sorghastrum species are adapted to different ecological conditions, such as woodlands, savannas, scrub-like vegetation, and even marshes and bogs. Morphological, anatomical, and cytological surveys support the decision of classifying Sorghastrum as a true taxonomic entity. By means of a phylogenetic analysis using cladograms, a preliminary hypothesis pointing out relationships between related genera, as well as among the species of the genus are suggested. Based on the phylogenetic analysis, as well as present and past distribution patterns, a working hypothesis explaining possible place and time of origin of the genus is proposed.