Lushly littering Garage Square in Moscow, thousands of faux petals, the fragile yellow flowers of Caribbean Roble Amarillo trees, have fallen under Russian trees of another species. A spectral reminder of a blossoming that never occurred, “Graft” calls attention to both deforestation and dwindling biodiversity due to climate change. Jennifer Allora and Guillermo Calzadilla, artists based in Puerto Rico, crafted the flowers as a call to environmental, political, and artistic action. —C.J.F.