q-Space plots obtained experimentally using pulsed field-gradient stimulated echo (PGSTE) nuclear magnetic resonance (NMR) spectroscopy from water diffusing in red blood cells (RBCs) of different canonical (distinct variant) morphologies have "signature" features. The experimental q-space plots from suspensions of stomatocytes, echinocytes and spherocytes generated chemically had no diffraction features; in contrast a sample of blood from a patient with hereditary spherocytosis showed diffraction minima. To understand the forms of q-space plots, mathematical/geometrical models of discocytes, stomatocytes, echinocytes and spherocytes were used as restricting boundaries in simulations of water diffusion with Monte Carlo random walks. These simulations indicated that diffusion-diffraction minima are expected for each of the cell shapes considered. The absence of diffusion-diffraction minima in stomatocytes generated by dithiothreitol treatment was surmised to be due to non-alignment of the cells with the magnetic field of the NMR spectrometer. Differential interference contrast microscopy images of the chemically generated spherocyte and echinocyte suspensions showed them to be heterogeneous in cell shape. Therefore, we concluded that the shape heterogeneity caused the loss of the diffusion-diffraction features, which were observed in the more homogeneous sample from a patient with hereditary spherocytosis, and in the simulations of homogeneous cell suspensions. This understanding of factors that affect q-space plots from RBC suspensions will assist morphological studies of other cell and tissue types.