A new crystal morphology (6 form) of poly(3-hydroxypropionate) (PHP) is found in cast and melt-crystallized PHPs with low molecular weight, in which the PHP chains possibly adopt a 2(1) helix rather than the trans conformation found in the beta or gamma form. The fusion temperature-and the crystallization temperature-dependent polymorphism are responsible for the dual morphologies and the unique growth kinetics of spherulites in the melt-crystallized PHPs.