LaNiO3 is locally distorted to orthorhombic at room temperature, and further to monoclinic at 200 K from globally rhombohedral structure. Such local rhombohedral phase hosts uncorrelated singlets, resulting in a pseudogap. Consequently, a crossover emerges at the rare earth nickelates phase diagram from fully gapped monoclinic long-range order to pseudogap monoclinic short-range order, as the radius of rare earth ions increases. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.