Honoring Hartmut Karl Lichtenthaler, innovative pioneer of photosynthesis, on his 90<sup>th</sup> birthday

We honor Professor Hartmut Karl Lichtenthaler, a versatile pioneer of photosynthesis research, plant physiology, isoprenoid biochemistry, and stress physiology of plants, for his groundbreaking and creative contributions to plant science. His innovative research on the chemical composition, ultrastructure, and function of chloroplasts and his detection of the major methylerythritol 4-phosphate (MEP) isoprenoid biosynthetic pathway in plants is key to our current understanding of the physiology and biochemistry of photosynthesis systems. His ingenious use of the powerful laser-induced chlorophyll <i>a</i> fluorescence imaging has helped us better understand the stress response processes in plant leaves. In this tribute, we present a summary of Lichtenthaler's career, significant scientific contributions, editorial engagement, promotion of international cooperation, many honors, and awards, as well as his devotion to hiking and mountaineering.