Carl Frederik Albert Christensen (1872–1942) was a Danish

Denmark

Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...

 systematic

Systematics

Biological systematics is the study of the diversification of terrestrial life, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...

 botanist. He graduated in natural history

Natural history

Natural history is the scientific research of plants or animals, leaning more towards observational rather than experimental methods of study, and encompasses more research published in magazines than in academic journals. Grouped among the natural sciences, natural history is the systematic study...

 from the University of Copenhagen

University of Copenhagen

The University of Copenhagen is the oldest and largest university and research institution in Denmark. Founded in 1479, it has more than 37,000 students, the majority of whom are female , and more than 7,000 employees. The university has several campuses located in and around Copenhagen, with the...

 under professor Eugenius Warming

Eugenius Warming

Johannes Eugenius Bülow Warming , known as Eugen Warming, was a Danish botanist and a main founding figure of the scientific discipline of ecology...

. He was first school teacher in Copenhagen

Copenhagen

Copenhagen is the capital and largest city of Denmark, with an urban population of 1,199,224 and a metropolitan population of 1,930,260 . With the completion of the transnational Øresund Bridge in 2000, Copenhagen has become the centre of the increasingly integrating Øresund Region...

, later superintendent at the Botanical Museum. He was a specialist in fern

Fern

A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...

s and published a catalogue of the World's Pteridophytes, Index Filicum

Index Filicum

Index Filicum is a continuing series of botanical indices geared to the ferns, or monilophyte clade. As of supplement 5, the index also covered the lycophytes , and also the horsetails...

. In addition, he authored a three-volume work on the history of botany

Botany

Botany, plant science, or plant biology is a branch of biology that involves the scientific study of plant life. Traditionally, botany also included the study of fungi, algae and viruses...

 in Denmark

Denmark

Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...

.

Selected scientific works

• Christensen, Carl (1905–06) Index Filicum
  Index Filicum
  Index Filicum is a continuing series of botanical indices geared to the ferns, or monilophyte clade. As of supplement 5, the index also covered the lycophytes , and also the horsetails...
  
  . 744 s. Index Filicum Supplementum I-III (1913–17). Reprint 1973 by Koeltz Antiquariat.
• Christensen, Carl (1924-1926) Den danske botaniks historie med tilhørende Bibliografi. København, H. Hagerups Forlag. Three vols. 680 s.