The role of the evolving array structure in the generation of crystal defects within a dendritic grain is investigated. Crystallographic perfection and associated defect structures are characterized using X-ray topography and optical microscopy. Observed structures are compared with quantitative descriptors of array order using a minimum spanning tree (MST) graph analysis. It is observed that the dendritic array structure evolves substantially over a growth length of 25 millimeters while the mosaic nature of the crystal remains relatively constant. The MST edge-length mean and standard deviation parameters are determined to be rather insensitive to differences in the local order due to statistical sampling size effects. This sample size dependence of the MST is evaluated with respect to its utility in distinguishing between square and hexagonal order, with varying degrees of superposed random noise. It is found that the MST distinguishing power is dramatically reduced when the sampling size is decreased below approximately 200 points. (C) 2004 Kluwer Academic Publishers.