Poly(trimethylene terephthalate) (PTT), a highly birefringent aromatic polyester, has been utilized to understand the mechanisms of crystal assembly into diversified types of banded spherulites. PTT exhibits three main types of banded spherulites (i.e., concentric, single-spiral, and doublespiral) co-existing in sample films melt-crystallized at 165 degrees C, regardless of sample thickness. The three types differ in their banding structures, interference color distributions, and nuclei geometries (S-shape, Z-shape, or dot-shape). Core diameter, band spacing ratio, and height difference (Delta z) around the core are the three key parameters of different banding patterns in PTT spherulites. Formation mechanism for three types of banded spherulites has been interpreted, and found to be highly correlated with the initial geometry shapes of their nuclei. (C) 2016 Wiley Periodicals, Inc.