Morphology and grain features of eleven species belong to six genera of amiIy Poaceae namely: Setaria viridis (L.) Beauv., Setaria pumila (Poiret) Roemer et Schultes, Panicum turgidum Forssk, Panicurn coloratum L., Echinoch!oa colonum (L.) ..jnk., Echinochloa crusgalli (L.) P.Beauv., Cenchrus ciIiaris L., Cenchrus echinatus Vahi., Brachiana reptans (L.) Gardner et Hubb., Brachiaria erucifomis (Sibth & Sm.) Gnseb. and Paspalidium gemiria turn (Forssk.) Stapf were studied. The objective of this investigation was to distinguish the relationship among the studied species (OTUs Operational Taxonomic Unit) by using their iorphological characters and the Scanning Electron Microscopy (SEM) of their grain surfaces. Single Linkage Clustering analysis technique was carried out to analyze these features. . From the morphological results, it could be recognized that the species of genus Panicum (P. turgidum and P. coloratum) were more close, firstly, to each Dther then to S. pumila. Also, the species represent genus Echinochloa (E. colonum and E. crus gaul) were close, firstly to S. viridis, then to the cluster included species of Panicum and Setaria. The only surprising result was with the species represent genus Cenchrus; where C.echinatus joined with Panicum cluster, while C. ciIiaris ‘inked with the cluster included species of genus Brachiaria and Paspa!idium gemma turn. Grain surface sculptures appearance and shape are considered the most diagnostic taxonomic characters to differentiate among the studied species. There are eleven features of the grain surface sculptures were observed by using SEM. The numerical technique analysis showed that, on the highest taxonomic similarity level 1.14, the studied species divided into two major clusters; one included species of Brachiaria, Cenchrus and Paspilidium and the other contained two clusters; one with species of genus Panicum, C. echinatus and S. pumila. The other with species of genus Echinochoa and S.virdis. Key using morphological and grain surface features was proposed.