M. H.  Grayum and Churchill, H. W., ?AN INTRODUCTION TO THE PTERIDOPHYTE FLORA OF FINCA LA SELVA, COSTA-RICA?, American Fern Journal, vol. 77, pp. 73-89, 1987.

M. H.  Grayum and Churchill, H. W., ?THE VASCULAR FLORA OF LA SELVA BIOLOGICAL STATION COSTA RICA LYCOPODIOPHYTA?, Selbyana, vol. 11, pp. 61-65, 1989.

M. H.  Grayum and Churchill, H. W., ?THE VASCULAR FLORA OF LA SELVA BIOLOGICAL STATION COSTA RICA POLYPODIOPHYTA?, Selbyana, vol. 11, pp. 66-118, 1989.

B. E.  Hammel and Grayum, M. H., ?PRELIMINARY-REPORT ON THE FLORA PROJECT OF LA-SELVA FIELD STATION, COSTA-RICA?, Annals of the Missouri Botanical Garden, vol. 69, pp. 420-425, 1982.