He authored studies on the history of botany and on medical botany. As a thinker on biological phenomena, Grecescu was an adherent of the Pasteurian theory on the genesis of organisms, rejecting the notion of spontaneous generation. Regarding evolution, he was strongly influenced by the then-current ideas of Lamarckism and opposed to the creationist paradigm. As director of the botanical garden, he contributed to its organization and systematization along scientific lines, and also intensified exchanges with foreign colleagues. He put together two valuable herbaria, one for the flora of Romania and another covering Europe. Along with the building of the botanical institute, these were destroyed in the April 1944 bombing of Bucharest.