Karl Theodor Hartweg (1812-1871) was a German botanist. He collected numerous new species of plants in Colombia, Ecuador, Guatemala, Mexico and California in the United States, collecting for the London Horticultural Society. Many of the species he discovered were formally published, with attribution, by George Gordon, the Foreman of the LHS Gardens and a specialist in the conifers which were well-represented in Hartweg's collections.

The standard botanical abbreviation Hartw. is applied to plants named by him.