Herbaria, collections of preserved plant specimens, have existed for 500 years as repositories of information about plants. Many of these collections are now being digitized, making them available to a much broader audience including students and teachers. Specimens can be used in a variety of different contexts in teaching biology, including from the viewpoint of the history of science. There are plants collected on Captain Cook's and Darwin's round-the-world voyages, as well as on early explorations of the western United States. Besides being tied to the history of science and culture, older specimens also document environmental variations over time, such as changes in flowering or fruiting times due to global warming. With access to digital images and information, teachers can design activities in which students test hypotheses and search for supporting evidence as they learn about collectors and the indigenous peoples who assisted them.