JØRGEN KRISTIANSEN (20 July 1931–18 May 2024)

Jørgen began studies at the University of Copenhagen in 1950. As an undergraduate, he studied botany from famous phycologists (J. Boye Petersen, Tyge Christensen) as well as other famous botanists (e.g. Tyge Böcher, Morten Lange). In 1957, Jørgen graduated with “distinction” after preparing a thesis on flagellates, and he received the prestigious Copenhagen University’s Gold Medal, awarded for a thesis of the highest quality (Fig. 1). He accepted a postgraduate fellowship at the Freshwater Biological Laboratory in Hillerød. Here, he continued his study of phytoplankton and limnology with Prof. Kaj Berg and Gunnar Nygaard. In 1960, he was hired as an Assistant Professor in the Department of Plant Anatomy and Cytology (University of Copenhagen) by Prof. Böcher. Recognizing the importance of electron microscopy, Jørgen attended an EM course at the Rockefeller Institute (New York, USA), and returned to study the silica scales of Synura splendida as a continuation of Boye Petersen’s studies on scaled chrysophytes. And so began Jørgen’s life-long study of scaled chrysophytes, for which he is most remembered. Jørgen also learned additional EM techniques from Irene Manton and Gordon Leedale at Leeds University (United Kingdom), and he lived in the same college with Hans Ettl, who was visiting from Prague. Jørgen’s teaching experience included (a) plant anatomy, morphology and embryology, (b) structure, taxonomy and ecology of algae, (c) freshwater phytoplankton, (d) form and function of algae, (e) taxonomy and evolution of algae, and so forth.

Figs 1–5. Jørgen Kristiansen.

Fig. 1. Jørgen Kristiansen with plankton sample from Botanisk Haves Dam, Copenhagen, ca. 1956. (Photo courtesy of Peter Kristiansen).

Fig. 2. Aase and Jørgen Kristiansen’s wedding photograph on 4 April 1959. (Photo courtesy of Peter Kristiansen).

Fig. 3. Jørgen Kristiansen using a field microscope during a collection trip at the First International Chrysophyte Symposium, August 1983. (Photo courtesy of Robert Andersen).

Fig. 4. Peter Siver and Jørgen Kristiansen at the Eighth International Chrysophyte Symposium held in Prague on August 2012. (Photo courtesy of Manuel Lizarralde).

Fig. 5. Jørgen Kristiansen’s tombstone. He is buried in Birkerød, at an old cemetery that has been in use for over 850 years. (Photo courtesy of Peter Kristiansen).

Jørgen began working at the Institute for Spore Plants (University of Copenhagen) in 1985 when Prof. Böcher died and the Plant Anatomy and Cytology Department was dissolved. At the new department, Jørgen joined Tyge Christensen, Øjvind Moestrup, Helge Thomsen, Helle Nielsen, Poul Møller Pedersen and Aase, his wife. Jørgen helped organize the Second International Phycological Congress, which was held in Copenhagen. At the Fifth International Phycological Congress in Qingdao, Jørgen organized a workshop on Biogeography of Freshwater Algae, an area where he also excelled. Jørgen served on the executive board of the Danish Botanical Society (chairman 1976–1982) and the International Phycological Society (1987–1989) as well as the vice president of the British Phycological Society (1985–1987). He was involved with the organization of numerous congresses and symposia, especially the International Chrysophyte Symposia. Jørgen contributed to the editorial work of several journals (e.g. Nordic Journal of Botany, Archiv für Protistenkunde, Algologial Studies) and was co-editor of several books and proceedings (see supplemental materials).

Jørgen travelled widely throughout the world (e.g. Greenland, several South American countries, North America, China and many European countries). The silica-scale scientists always knew when Jørgen visited a new place because he then published a paper with the silica-scaled algae from that country. Jørgen formally retired from the University of Copenhagen in 2001 when he reached the age of 70, but with emeritus status, he continued working and publishing books. Most notable are Encyclopaedia of Chrysophyte Genera (Kristiansen & Preisig, 2001), Golden Algae (Kristiansen, 2005), and Synurophyceae; Süsswasserflora von Mitteleuropa (Kristiansen & Preisig, 2007).

Jørgen Kristiansen was born near the centre of Jutland Peninsula, in the city of Vejle, Denmark. His father (Hans Johan Rudolf Kristiansen), and his grandfather (Peter Rudolf Theodor Kristiansen), were both school teachers. Specifically, they taught languages, and Jørgen was fluent in several languages. Jørgen’s mother, Ingrid, was the daughter of the master painter Ludvig Jensen. This, too, seemed to contribute to Jørgen’s scientific career because he applied his artistic talents to the study of phytoplankton. Jørgen had one brother, Ole, who was four years younger. By all accounts, Jørgen grew up in a warm and loving family, with an emphasis on education and religion. World War II impacted Jørgen’s life. The Germans occupied Vejle and other parts of Denmark for much of the war, and Jørgen recalled blackouts, boarded buildings, many hardships and shortages as well as occasional bombs and explosions.

Jørgen attended grammar school and high school in Vejle, where he excelled. In 1952, during his University of Copenhagen studies, he met Aase. He disembarked from a bus, and there was “a girl with a student cap and bicycle”. There was an immediate attraction as they walked together that day, and their friendship grew. Aase was also studying algae, which must have contributed to their relationship. They were married on 4 April 1959 after Jørgen had completed a year serving in the Danish Civil Defence Force (Fig. 2). They had two sons, Peter (born 25 August 1961) and Erik (born 31 July 1965). Jørgen and Aase often travelled together, and if you knew one of them, then you knew the other too. They celebrated their 65th wedding anniversary in 2024. Jørgen is survived by Aase, sons Peter and Erik as well as grandchildren Tobias and Gustav.

Although Jørgen loved and studied many different algal groups, he was world renowned for his work on chrysophytes, especially siliceous-scaled taxa (Fig. 3). He collaborated with many colleagues, but his work with Berit Asmund was extensive, culminating in a monograph on Mallomonas (Asmund & Kristiansen, 1986). It was a major effort using light and electron microscopy of scale morphology to organize that genus into taxonomic sections and series. The background information, detailed descriptions, electron micrographs and distributional records served as the foundation for hundreds of subsequent studies, and as the “Bible” for young phycologists following in their footsteps. Jørgen continued to rigorously edit and add to the monograph that resulted in an updated publication (Kristiansen, 2002), which remains a widely used and referenced work today.

Jørgen, with great enthusiasm, organized several freshwater phycology field trips for Master’s Degree students (see supplemental materials) as well as colleagues. The trips went to the Laboratory at Salten Skov, Silkesborg (Jutland, Denmark) or the Aneboda Field Station (Sweden). The latter often included Gertrud Cronberg from the University of Lund. Colleagues recall that the departmental van was packed with sampling equipment and microscopes, and, if space allowed, some personal items. On one trip, the lakes near Silkeborg were found to be ice-covered, and therefore a hole was made in the ice to allow a plankton net to be dropped into the water. Much to the participants’ surprise (but not Jørgen’s) the samples contained live phytoplankton. Though the main focus of the excursion was species diversity of freshwater phytoplankton, Jørgen also shared his great knowledge of land plants, birds and nature in general.

Jørgen had a most prolific career, authoring or co-authoring two books, eight edited books, and 137 peer-reviewed papers (see supplemental materials). In addition to the many generic section and series descriptions, Jørgen named two genera, 28 species and subspecific taxa, as well as proposing 19 combinations. Two species, Mallomonas kristiansenii and Synura kristiansenii, have been named in his honour, representing his two most favourite genera (see supplemental materials). As his career progressed Jørgen became increasingly interested in chrysophyte biogeographic patterns and the use of silica-scaled algae as bioindicators. Using his direct knowledge and a comprehension review of the literature, he classified taxa as, for example, cosmopolitan, bipolar, temperate, tropical or endemic species. His designations provide testable hypotheses for future molecular studies. Tracing Jørgen’s career investigating freshwater flagellates, over time he went from light microscopy to adding transmission electron microscopy, then realizing the significance of scanning electron microscopy, this was added, and finally he embraced molecular data; he fully understood the advantages of each technique.

Jørgen is perhaps best known for his role in the International Chrysophyte Symposia (ICS). Jørgen was an invited speaker (supported by the USA National Science Foundation) at the First ICS held in Grand Forks, North Dakota, and he was co-editor of the Proceedings from that meeting. Subsequent ICS were held approximately every four years, and Jørgen became the primary driving force for that continued success. He was co-organizer for several symposia, and he co-edited five of the six symposia volumes between 1983 and 2004. Jørgen was specifically honoured at the Seventh ICS held in New London, CT in 2008 to acknowledge his many contributions. By the Seventh ICS only three people (Jørgen, Gertrud Cronberg and PAS) had attended all of the symposia. His health failing, Jørgen still managed to participate in the Prague meeting in 2012 which sadly was his last (Fig. 4). A tribute (celebration) to Jorgen is planned for the forthcoming ICS in Korea (2025). Jørgen Kristiansen, passed away on 18 May 2024 at the age of 92. In a tribute fitting to a world class scientist who loved chrysophytes, his tombstone bears an image of Mallomonas kristiansenii that was named in his honour (Fig. 5).

ACKNOWLEDGEMENTS

We thank Niels Daugbjerg, Gert Hansen, Peter Kristiansen, Øjvind Moestrup and Helge Thomsen for providing a copy of Jørgen’s autobiography (unpublished), curriculum vitae list of publications and photographs as well as for reviewing this manuscript.

SUPPLEMENTARY MATERIAL

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00318884.2024.2378682