The seed morphology of six species, representing genera of Hyoscyamus L. (Solanaceae) in Turkey was investigated using a binocular stereomicroscope and scanning electron microscopy (SEM), to determine the significance of seed coat features as taxonomic characters. Macro and micromorphological characters, including seed shape, size, hilum position and character, seed coat appearance, cell shape, sculpture characteristics of cell walls and wall ornemantation are presented. The results indicate that the seed coat sculpture is cerebelloid in H. pussillus and reticulate or reticulate-puzzle in all the remaining species. Two types of testal cells can be identified based on their general shape and linearity of the anticlinal walls. In one type, the cell shape is oblong to subpolygonal, with the anticlinal wall being sinuate to repandate; in the other type, the cell is triangular to subpolygonal, with the anticlinal wall straight or slightly curved. Fine ornamentation of the anticlinal walls of the testal cells varies from smooth to covered with, fibril, punctate or papillate projections. However, the size and shape of seeds and the position of hilum have partly systematic significance.