[1][2] As a student, Weigend received first prize in 1987 and 1989 as part of the Federal President's history competition on the subject of environmental history and in 1992 from the South African Phycological Society for his studies on the phytochemistry of South African macroalgae.
As part of his research, he traveled to Venezuela, Colombia, Ecuador and Peru before commencing in July 1997 with his dissertation Nasa and the conquest of South America – Systematic Rearrangements in Loasaceae Juss.
As part of this work, Weigend presented a complete revision of the flower nettle family (Loasaceae) and re-described numerous genera and species, but due to a technical error the taxa had to be revalidated in 2006.
[3] From 1999, Weigend began research on the genera Ribes and Desfontainia; in 2000 he became an assistant professor at the Institute for Systematic Botany and Phytogeography at the Free University of Berlin.
[6] Weigend has edited the Loasaceae for several standard works, such as in 2001 for the Flora de Colombia and in 2004 for the sixth volume of the Families and Genera of Vascular Plants.