Constantin Georg Alexander Winkler was a Russian botanist of Baltic-German heritage.
From 1871 to 1874 he studied botany at the University of Dorpat, where from 1874 to 1879, he worked as an assistant to Edmund Russow at the botanical garden. In the meantime he taught classes in natural sciences at several schools. From 1879 to 1899 he was associated with the Saint Petersburg Botanical Garden; as curator of its herbarium and as head botanist. At Saint Petersburg he played a major role in reorganization of its herbaria and the greenhouse collections. In 1899 he relocated to the town of Wesenberg, where he died the following year.
He is known for his work in the field of plant systematics, and was the taxonomic authority of many species within the botanical family Asteraceae. The genus Winklera commemorates his name, as do a number of species with the epithet of winkleri; as an example, Iris winkleri.