Using herbarium specimens spanning 133 years and field-collected measurements, we assessed intraspecific trait (leaf structure and stomata) variability from grass species in the Great Plains of North America. We focused on two widespread, closely-related grasses from tribe Paniceae: Dichanthelium oligosanthes subsp. scribnerianum (C3) and Panicum virgatum (C4). Thirty-one specimens per taxon were sampled from local herbaria from the years 1887 – 2013 to assess trait responses across time to changes in atmospheric [CO2] and growing season precipitation and temperature.