Thorvald (Thorwald) Julius Sørensen (4 July 1902 – 21 June 1973) was a Danish

botanist Botany, also called plant science, is the branch of natural science and biology studying plants, especially Plant anatomy, their anatomy, Plant taxonomy, taxonomy, and Plant ecology, ecology. A botanist or plant scientist is a scientist who s ...

and

evolutionary biologist Evolutionary biology is the subfield of biology that studies the evolutionary processes such as natural selection, common descent, and speciation that produced the diversity of life on Earth. In the 1930s, the discipline of evolutionary biol ...

Biography

Sørensen was professor at the Royal Veterinary and Agricultural University 1953–1955 and at the

University of Copenhagen The University of Copenhagen (, KU) is a public university, public research university in Copenhagen, Copenhagen, Denmark. Founded in 1479, the University of Copenhagen is the second-oldest university in Scandinavia, after Uppsala University. ...

1955–1972. He was director of the Copenhagen Botanical Garden and Botanical Museum during the same period. Thorvald Sørensen spent the years 1931–1935, based on Ella Island, studying plants in the then little known North-East

Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...

. He published the botanical research of the Three-year Expedition to East Greenland. He also published a doctoral thesis on the annual

phenological Phenology is the study of periodic events in biological life cycles and how these are influenced by seasonal and interannual variations in climate, as well as habitat factors (such as elevation). Examples include the date of emergence of leave ...

rhythm of the High Arctic plant species, including the

pollination Pollination is the transfer of pollen from an anther of a plant to the stigma (botany), stigma of a plant, later enabling fertilisation and the production of seeds. Pollinating agents can be animals such as insects, for example bees, beetles or bu ...

of their flowers (1941). He critically revised the

flora and sorted out

taxonomy image:Hierarchical clustering diagram.png, 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme o ...

of a number of difficult

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

, most notably ''

Puccinellia ''Puccinellia'' is a genus of plants in the Poaceae, grass family, known as alkali grass or salt grass. These grasses grow in wet environments, often in Saline water, saline or alkaline conditions. They are native to temperate to Arctic regions ...

''. He carried out a number of studies in the

evolutionary biology Evolutionary biology is the subfield of biology that studies the evolutionary processes such as natural selection, common descent, and speciation that produced the diversity of life on Earth. In the 1930s, the discipline of evolutionary biolo ...

of plants, such as ''

Taraxacum ''Taraxacum'' () is a genus of flowering plants in the family Asteraceae, which consists of species commonly known as dandelions. The scientific and hobby study of the genus is known as taraxacology. The genus has a near-cosmopolitan distribu ...

'', ''

Capsella bursa-pastoris ''Capsella bursa-pastoris'', known as shepherd's purse or lady's purse because of its triangular flat fruits, which are purse-like, is a small annual and ruderal flowering plant in the mustard family (Brassicaceae). Scientists have referred to ...

'' and ''

Ranunculus ''Ranunculus'' is a large genus of about 1750 species of flowering plants in the family Ranunculaceae. Members of the genus are known as buttercups, spearworts and water crowfoots. The genus is distributed worldwide, primarily in temperate an ...

''. He developed a quotient of similarity in

species composition Relative species abundance is a component of biodiversity and is a measure of how common or rare a species is relative to other species in a defined location or community.Hubbell, S. P. 2001. ''The unified neutral theory of biodiversity and biogeog ...

between plant communities—the still much-used Sørensen similarity index. He illustrated its use on a data set collected in Danish

grassland A grassland is an area where the vegetation is dominance (ecology), dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes such as clover, and other Herbaceo ...

by Johannes Grøntved (1882-1956), who used the quantitative method to sample vegetation developed by Christen C. Raunkiær (1860–1938).

Selected plant names he published

*'' Braya intermedia'' T.J.Sørensen (1954) in Meddelelser om Grønland 134 (8). *''

Puccinellia groenlandica ''Puccinellia'' is a genus of plants in the grass family, known as alkali grass or salt grass. These grasses grow in wet environments, often in saline or alkaline conditions. They are native to temperate to Arctic regions of the Northern and ...

'' T.J.Sørensen (1953) in Meddelelser om Grønland 134 (3).

Honours

The Arctic campion species '' Silene sorensenis'' and Th. Sørensen Land in Greenland were named in his honour.

Selected publications

*Sørensen, T. (1935) Bodenformen und Pflanzendecke in Nordostgrönland. Beiträge zur Theorie der polaren Bodenversetzungen auf Grund von Beobachtungen über deren Einfluss auf die Vegetation in Nordostgrönland. Meddelelser om Grønland 93 (4). *Sørensen, T. (1941) Temperature relations and

phenology Phenology is the study of periodic events in biological life cycles and how these are influenced by seasonal and interannual variations in climate, as well as habitat factors (such as elevation). Examples include the date of emergence of leav ...

of the Northeast

flowering plants. Meddelelser om Grønland 129: 1–305. *Sørensen, T. (1942) Untersuchungen über die Therophytengesellschaften auf den isländischen Lehmflächen ("Flags"). Biologiske Skrifter / Kongelige Danske Videnskabernes Selskab 2 (2). *Sørensen, T. and Gudjónsson, Gudni (1946) Spontaneous chromosome-aberrants in apomictic Taraxaca: morphological and cyto-genetical investigations. Biologiske Skrifter / Kongelige Danske Videnskabernes Selskab 4 (2). *Sørensen, T. (1948) A method of establishing groups of equal amplitude in plant sociology based on similarity of species and its application to analyses of the vegetation on Danish commons. Biologiske Skrifter / Kongelige Danske Videnskabernes Selskab 5: 1-34. *Sørensen, T. (1953) A Revision of the Greenland Species of ''

'' Parl. With contribution to our knowledge of the Arctic ''

'' flora in general. Meddelelser om Grønland 136 (3) 1–179. *Jørgensen, C.A., Sørensen, T. and Westergaard, M. (1958) The Flowering Plants of Greenland. Biologiske Skrifter / Kongelige Danske Videnskabernes Selskab 9 (4).

References

Other sources

*Obituary in Botanisk Tidsskrift 68 (2): 165-168 (1973) {{DEFAULTSORT:Sorensen, Thorvald Botanists active in the Arctic 20th-century Danish botanists Danish ecologists 20th-century Danish biologists University of Copenhagen alumni Academic staff of the University of Copenhagen 1902 births 1973 deaths