G.  Kjellberg and Christensen, C., ?Pteridophyta von Celebes gesammelt von G. Kjellberg 1929?, Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie. Leipzig, vol. 66, pp. 39-70, 1934.

C.  Christensen, Index Filicum. Copenhagen: H. Hagerup, 1906, p. 9+744.

C.  Christensen, Index Filicum. Supplementum 1906-1912. Copenhagen: H. Hagerup, 1913.

C.  Christensen, Index Filicum Supplément préliminaire . Hafniae: Hagerup, 1917.

C.  Christensen, ?On a collection of Pteridophyta from Celebes leg. Dr. W. Kaudern?, Sv.Bot.Tids., vol. 16, pp. 88-102, 1922.

C.  Christensen, ?Asiatic Pteridophyta collected by Joseph F. Rock 1920-1923?, Contributions from the United States National Herbarium. Smithsonian InstitutionContributions from the United States National Herbarium. Smithsonian Institution, vol. 26, pp. 265-337, 1931.

C.  Christensen, ?Annotationes et corrigenda ad Wu, Wong et Pong: Polypodiaceae Yaoshanensis, Kwangsi?, Bulletin of the Department of Biology, College of Science, Sun Yatsen University Bulletin of the Department of Biology, College of Science, Sun Yatsen University, vol. 6, 1933.

C.  Christensen, Index Filicum Suppl. III. Copenhagen: H. Hagerup, 1934, p. 219.

C.  Christensen, ?Taxonomic fern studies III. Revision of the genera and species of ferns described by A.J. Cavanilles?, Dansk Botanisk Arkiv Udgivet af Dansk Botanisk Forening. CopenhagenDansk Botanisk Arkiv Udgivet af Dansk Botanisk Forening. Copenhagen, vol. 9  , pp. 3-32, 1937.

C.  Christensen, ?A revision of the Pteridophyta of Samoa?, Bulletin of the Bernice P. Bishop Museum, vol. 177  , 1943.

C.  Christensen and Holttum, R. E., ?The Ferns of Mount Kinabalu?, Gardens' Bull.Straits Settlements, vol. 7  , pp. 191-324, 1934.

C.  Christensen, ?Taxonomic fern studies V. Descriptions of 36 new Species of Ferns?, Dansk Botanisk Arkiv Udgivet af Dansk Botanisk Forening. Copenhagen, vol. 9  , pp. 53-78, 1937.

C.  Christensen, ?Report of Mount Pinatubo ferns?, Leaflets of Philippine Botany. Manila, vol. 9, pp. 3139-3172, 1933.

C.  Christensen, ?Pteridophyta in insula Quelpaert a cl. P. Taquet anno 1910 lecta?, Bulletin de Géographie Botanique, vol. 20, pp. 69-72, 1911.

C.  Christensen, ?New or noteworthy Papuan ferns?, Brittonia; a Series of Botanical Papers. New York, NY, vol. 2, 1937.