V. C.  Pence, Charls, S. M., Plair, B. L., Lindsey, K., and Winget, G. D., ?Propagation and cryopreservation of Todsen's permyroyal (Hedeoma todsenii) in vitro?, In Vitro Cell Dev-An, vol. 43. pp. S31?S32, 2007.