Castellanos, M.C.; Wilson, P.; Thomson, J.D. 2002. Dynamic nectar replenishment in flowers of Penstemon (Scrophulariaceae). American Journal of Botany. 89(1): 111-118.

Castellanos, M.C.; Wilson, P.; Thomson, J.D. 2002. Dynamic nectar replenishment in flowers of Penstemon (Scrophulariaceae). American Journal of Botany. 89(1): 111-118.