Mitchell, M. E., Knowles, M. C., & Porter, L. L. o. I. (1998). Index of collectors in Knowles' The lichens of Ireland (1929) and Porter's supplement (1948): With a conspectus of lichen recording in the Irish vice-counties to 1950. National Botanic Gardens, Glasnevin.

Mitchell, M. E., et al. Index of Collectors in Knowles' The Lichens of Ireland (1929) and Porter's Supplement (1948): With a Conspectus of Lichen Recording in the Irish Vice-counties to 1950. National Botanic Gardens, Glasnevin, 1998.