Centimeter-length needle crystals melt self-similarly in microgravity prior to the on-set of rapid shape change, as melting reduces crystallite lengths below ~5mm. Large axial ratios fell by an order-of-magnitude as needle-crystals spheroidize. The cause of this surprising shape change and its radical departure from self-similar melting is investigated using the Reynolds transport theorem. Leibniz-Reynolds analysis shows that where capillary energy is released normal interface speed accelerates during melting and slows during growth. Conversely, where capillary energy is removed from an interface, its speed slows during melting and accelerates during growth. Irrespective of whether a crystal melts or grows, autogenous modulations reverse at ‘Laplace points’. Where these countervailing perturbations occur on morphologically unstable interfaces, inflection and ‘curling’ result, which promote pattern complexity. Dynamic simulations of interface patterns using phase field and other numerical methods confirm quantitatively that inflection/branching initiates precisely at ‘Laplace points’ predicted analytically from the Reynolds theorem.