The isothermal crystallization from the melt of a poly(1,3-dioxolan) having a number-average molecular weight of 5100 was investigated by optical microscopy, differential scanning calorimetric and X-ray diffraction. A single spherulitic morphology (Phase I) of negative sign is observed at crystallization temperatures below 19 C while multiple morphologies are observed at crystallization temperatures above 19 degrees C (Phases IIa, IIb and III). Phase ha crystallizes first and is characterized by a low birefringence until its sporadic transformation into Phase lib, characterized by a sudden increase in birefringence. Phase lib acts as a nucleating agent for Phase III (cross-nucleation process). Phases I and III exhibit distinct growth rates that are two orders of magnitude lower than the transformation rate of Phase ha into Phase Jib. Relationships between the crystalline structures of the different morphologies and their melting temperatures are also discussed. The transformation IIa/IIb is easily detected optically by a huge increase in birefringence but there is a more subtle Ia/Ib transformation which is hardly seen optically, although it gives rise to a large increase in melting temperature of that phase. (C) 2011 Elsevier Ltd. All rights reserved.