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• Marcussen, Thomas; Ballard, Harvey E.; Danihelka, Jiří; Flores, Ana R.; Nicola, Marcela V. & Watson, John M. (2022). A Revised Phylogenetic Classification for Viola (Violaceae). Plants. ISSN 2223-7747. 11(17). doi: 10.3390/plants11172224. Full text in Research Archive
• Scoppola, Anna; Cardoni, Simone; Marcussen, Thomas & Simeone, Marco Cosimo (2022). Complex Scenarios of Reticulation, Polyploidization, and Species Diversity within Annual Pansies of Subsect. Bracteolatae (Viola Sect. Melanium, Violaceae) in Italy: Insights from 5S-IGS High-Throughput Sequencing and Plastid DNA Variation. Plants. ISSN 2223-7747. 11(10). doi: 10.3390/plants11101294. Full text in Research Archive
• Ammarellou, Ali; Żabicka, Justyna; Słomka, Aneta; Bohdanowicz, Jerzy; Marcussen, Thomas & Kuta, Elżbieta (2021). Seasonal and simultaneous cleistogamy in rostrate violets (Viola, subsect. rostratae, violaceae). Plants. ISSN 2223-7747. 10(10), p. 1–13. doi: 10.3390/plants10102147. Full text in Research Archive
• Lindberg, Camilla Lorange; Hanslin, Hans Martin; Schubert, Marian; Marcussen, Thomas; Trevaskis, Ben & Preston, Jill Christine [Show all 7 contributors for this article] (2020). Increased above-ground resource allocation is a likely precursor for independent evolutionary origins of annuality in the Pooideae grass subfamily. New Phytologist. ISSN 0028-646X. 228(1), p. 318–329. doi: 10.1111/nph.16666. Full text in Research Archive Show summary

  Semelparous annual plants flower a single time during their 1‐yr life cycle, investing much of their energy into rapid reproduction. By contrast, iteroparous perennial plants flower multiple times over several years, and partition their resources between reproduction and persistence. To which extent evolutionary transitions between life‐cycle strategies are internally constrained at the developmental, genetic and phylogenetic level is unknown. Here we study the evolution of life‐cycle strategies in the grass subfamily Pooideae and test if transitions between them are facilitated by evolutionary precursors. We integrate ecological, life‐cycle strategy and growth data in a phylogenetic framework. We investigate if growth traits are candidates for a precursor. Species in certain Pooideae clades are predisposed to evolve annuality from perenniality, potentially due to the shared inheritance of specific evolutionary precursors. Seasonal dry climates, which have been linked to annuality, were only able to select for transitions to annuality when the precursor was present. Allocation of more resources to above‐ground rather than below‐ground growth is a candidate for the precursor. Our findings support the hypothesis that only certain lineages can respond quickly to changing external conditions by switching their life‐cycle strategy, likely due to the presence of evolutionary precursors.

• Kwiatkowska, Monika; Żabicka, Justyna; Migdałek, Grzegorz; Żabicki, Piotr; Cubala, Marlena & Bohdanowicz, Jerzy [Show all 13 contributors for this article] (2019). Comprehensive characteristics and genetic diversity of the endemic Australian Viola banksii (section Erpetion, Violaceae). Australian Journal of Botany. ISSN 0067-1924. 67(2), p. 81–98. doi: 10.1071/BT18233.
• Bravo, Gustavo A.; Antonelli, Alexandre; Bacon, Christine D.; Bartoszek, Krzysztof; Blom, Mozes P.K. & Huynh, Stella [Show all 20 contributors for this article] (2019). Embracing heterogeneity: Coalescing the tree of life and the future of phylogenomics. PeerJ. ISSN 2167-8359. 2019(2), p. 1–60. doi: 10.7717/peerj.6399. Full text in Research Archive
• Kwiatkowska, Monika; Bohdanowicz, Jerzy; Cubala, Marlena; Slomka, Aneta; Zabicka, Justyna & Zabicki, Piotr [Show all 10 contributors for this article] (2019). A new pollination system in non-cleistogamous species of Viola results from nyctinastic (night-closing) petal movements – A mixed outcrossing-selfing strategy. Flora: Morphologie, Geobotanik, Oekophysiologie. ISSN 0367-2530. 253, p. 1–9. doi: 10.1016/j.flora.2019.01.007.
• Huynh, Stella; Marcussen, Thomas; Felber, Francois & Parisod, Christian (2019). Hybridization preceded radiation in diploid wheats. Molecular Phylogenetics and Evolution. ISSN 1055-7903. 139, p. 1–10. doi: 10.1016/j.ympev.2019.106554.
• Schubert, Marian; Marcussen, Thomas; Meseguer, Andrea S. & Fjellheim, Siri (2019). The grass subfamily Pooideae: Cretaceous–Palaeocene origin and climate‐driven Cenozoic diversification . Global Ecology and Biogeography. ISSN 1466-822X. 28(8), p. 1168–1182. doi: 10.1111/geb.12923. Full text in Research Archive
• Blaxland, Kim; Ballard, Harvey E. & Marcussen, Thomas (2018). Viola pluviae sp. nov. (Violaceae), a member of subsect. Stolonosae in the Pacific Northwest region of North America. Nordic Journal of Botany (NJB). ISSN 0107-055X. 36(9), p. 1–9. doi: 10.1111/njb.01931.
• Park, Sungkyu; Yoo, Ki-Oug; Marcussen, Thomas; Backlund, Anders; Jacobsson, Erik & Rosengren, K Johan [Show all 8 contributors for this article] (2017). Cyclotide evolution: Insights from the analyses of their precursor sequences, structures and distribution in violets (Viola). Frontiers in Plant Science. ISSN 1664-462X. 8. doi: 10.3389/fpls.2017.02058.
• Migdalek, Grzegorz; Nowak, J; Saluga, M; Cieslak, E; Szczepaniak, M & Ronikier, M [Show all 9 contributors for this article] (2017). No evidence of contemporary interploidy gene flow between the closely related European woodland violets Viola reichenbachiana and V. riviniana (sect. Viola, Violaceae). Plant Biology. ISSN 1435-8603. 19(4), p. 542–551. doi: 10.1111/plb.12571.
• Oxelman, Bengt; Brysting, Anne Krag; Jones, Graham R; Marcussen, Thomas; Oberprieler, Christoph & Pfeil, Bernard E. (2017). Phylogenetics of Allopolyploids. Annual Review of Ecology, Evolution and Systematics. ISSN 1543-592X. 48, p. 543–557. doi: 10.1146/annurev-ecolsys-110316-022729. Full text in Research Archive
• Toprak, Zeynep; Pfeil, Bernard E; Jones, Graham; Marcussen, Thomas; Ertekin, Alaattin Selcuk & Oxelman, Bengt (2016). Species delimitation without prior knowledge: DISSECT reveals extensive cryptic speciation in the Silene aegyptiaca complex (Caryophyllaceae). Molecular Phylogenetics and Evolution. ISSN 1055-7903. 102, p. 1–8. doi: 10.1016/j.ympev.2016.05.024.
• Malobecki, Andrzej; Marcussen, Thomas; Bohdanowicz, Jerzy; Migdalek, Grzegorz; Slomka, Aneta & Kuta, Elzbieta (2016). Cleistogamy and phylogenetic position of Viola uliginosa (Violaceae) re-examined. Botanical journal of the Linnean Society. ISSN 0024-4074. 182(1), p. 180–194. doi: 10.1111/boj.12460.
• McKeown, Meghan; Schubert, Marian; Marcussen, Thomas; Fjellheim, Siri & Preston, Jill C (2016). Evidence for an early origin of vernalization responsiveness in temperate pooideae grasses. Plant Physiology. ISSN 0032-0889. 172(1), p. 416–426. doi: 10.1104/pp.16.01023.
• Knoche, Gerd & Marcussen, Thomas (2016). Viola barhalensis (Violaceae), a new species from northeastern Turkey. Phytotaxa. ISSN 1179-3155. 275(1), p. 14–22. doi: 10.11646/phytotaxa.275.1.2.
• Marcussen, Thomas; Heier, Lise; Brysting, Anne Krag; Oxelman, Bengt & Jakobsen, Kjetill Sigurd (2015). From gene trees to a dated allopolyploid network: insights from the angiosperm genus Viola (Violaceae). Systematic Biology. ISSN 1063-5157. 64(1), p. 84–101. doi: 10.1093/sysbio/syu071.
• Sandve, Simen Rød; Marcussen, Thomas; Mayer, Klaus F X; Jakobsen, Kjetill Sigurd; Heier, Lise & Steuernagel, Burkhard [Show all 8 contributors for this article] (2015). Chloroplast phylogeny of Triticum/Aegilops species is not incongruent with an ancient homoploid hybrid origin of the ancestor of the bread wheat D-genome. New Phytologist. ISSN 0028-646X. 208(1), p. 9–10. doi: 10.1111/nph.13487.
• Mohammadi Shahrestani, Maryam; Marcussen, Thomas; Saeidi Mehrvarz, Shahryar & Yousefi, Narjes (2015). Morphological and phylogenetic relationships within Viola sect. Sclerosium (Violaceae) in Iran. Flora: Morphologie, Geobotanik, Oekophysiologie. ISSN 0367-2530. 215, p. 67–74. doi: 10.1016/j.flora.2015.07.008.
• Bertrand, Yann J.K.; Scheen, Anne-Cathrine; Marcussen, Thomas; Pfeil, Bernard E.; de Sousa, Filipe & Oxelman, Bengt (2015). Assignment of homoeologs to parental genomes in allopolyploids for species tree inference, with an example from fumaria (papaveraceae). Systematic Biology. ISSN 1063-5157. 64(3), p. 448–471. doi: 10.1093/sysbio/syv004.
• Marcussen, Thomas; Sandve, Simen Rød; Heier, Lise; Spannagl, Manuel; Pfeifer, Matthias & The International Wheat Genom, IWGSC [Show all 11 contributors for this article] (2014). Ancient hybridizations among the ancestral genomes of bread wheat. Science. ISSN 0036-8075. 345(6194). doi: 10.1126/science.1250092.
• Nordal, Inger; Marcussen, Thomas & Elven, Reidar (2013). Viola rupestris F.W.Schmidt. In Elven, Reidar; Fremstad, Eli & Pedersen, Oddvar (Ed.), Distribution maps of Norwegian vascular plants. IV The eastern and northeastern elements. Akademika forlag. ISSN 978-82-321-0246-4. p. 453–455. doi: 10.1111/j.1365-2699.2005.01257.x.
• Elven, Reidar; Fremstad, Eli & Marcussen, Thomas (2013). Viola epipsila Ledeb. In Elven, Reidar; Fremstad, Eli & Pedersen, Oddvar (Ed.), Distribution maps of Norwegian vascular plants. IV The eastern and northeastern elements. Akademika forlag. ISSN 978-82-321-0246-4. p. 447–450.
• Marcussen, Thomas; Jakobsen, Kjetill Sigurd; Danihelka, Jiří; Ballard, Harvey E.; Blaxland, Kim & Brysting, Anne Krag [Show all 7 contributors for this article] (2012). Inferring Species Networks from Gene Trees in High-Polyploid North American and Hawaiian Violets (Viola, Violaceae). Systematic Biology. ISSN 1063-5157. 61(1), p. 107–126. doi: 10.1093/sysbio/syr096.
• Marcussen, Thomas & Borgen, Liv (2011). Species delimitation in the Ponto-Caucasian Viola sieheana complex, based on evidence from allozymes, morphology, ploidy levels, and crossing experiments. Plant Systematics and Evolution. ISSN 0378-2697. 291(3-4), p. 183–196. doi: 10.1007/s00606-010-0377-z.
• Brysting, Anne Krag; Mathiesen, Cecilie & Marcussen, Thomas (2011). Challenges in polyploid phylogenetic reconstruction: A case story from the arctic-alpine Cerastium alpinum complex. Taxon. ISSN 0040-0262. 60(2), p. 333–347. doi: 10.1002/tax.602004.
• Marcussen, Thomas; Oxelman, Bengt; Skog, Anna & Jakobsen, Kjetill Sigurd (2010). Evolution of plant RNA polymerase IV/V genes: evidence of subneofunctionalization of duplicated NRPD2/NRPE2-like paralogs in Viola (Violaceae). BMC Evolutionary Biology. ISSN 1471-2148. 10(45). doi: 10.1186/1471-2148-10-45.
• Malecot, V; Marcussen, Thomas; Munzinger, J; Yockteng, R & Henry, M (2007). On the origin of the sweet-smelling Parma violet cultivars (Violaceae): Wide intraspecific hybridization, sterility, and sexual reproduction. American Journal of Botany. ISSN 0002-9122. 94(1), p. 29–41.
• Marcussen, Thomas (2007). Lifiol er død - leve engfiol! en kritisk morfologisk gjennomgang av komplekset i Norge. Blyttia : Norsk botanisk forenings tidsskrift. ISSN 0006-5269. 65(3), p. 195–207.
• Marcussen, Thomas (2006). Allozymic variation in the widespread and cultivated Viola odorata (Violaceae) in western Eurasia. Botanical journal of the Linnean Society. ISSN 0024-4074. 151, p. 563–571.
• Marcussen, Thomas; Borgen, Liv & Nordal, Inger (2005). New distributional and molecular information call into question the systematic position of the West Asian Viola sintenisii (Violaceae). Botanical journal of the Linnean Society. ISSN 0024-4074. 147, p. 91–98.
• Nordal, Inger; Jonsell, Bengt & Marcussen, Thomas (2005). Viola rupestris: molecular analyses to elucidate postglacial migration in Western Europe. Journal of Biogeography. ISSN 0305-0270. 32, p. 1453–1459.
• Nordal, Inger & Marcussen, Thomas (2005). Kalkfiol Viola rupestris ssp. relicta er bisentrisk i Skandinavia - ny forekomst på Møre. Blyttia : Norsk botanisk forenings tidsskrift. ISSN 0006-5269. 63(2), p. 67–71.
• Marcussen, Thomas; Borgen, Liv & Nordal, Inger (2001). Viola hirta (Violaceae) and its relatives in Norway. Nordic Journal of Botany (NJB). ISSN 0107-055X. 21(1), p. 5–17. Show summary

  Viola hirta is widespread in most of Europe but rare in Norway, occurring in four isolated enclaves around the Oslo Fjord. Allozymic and morphological patterns of variation were studied in 320 individuals of Viola hirta (2n = 20) and its relatives V. collina (2n = 20), V. odorata (2n = 20), and V. suavis (2n = 40) from 22 Norwegian populations. Ongoing introgression from both V. collina and V. odorata, as hypothesised by several authors, was not supported by our data. All hybrids proved to be primary ones and, apparently, introgression is rare. However, allozyme markers suggested that V. hirta may have been affected by ancient introgression from V. collina and possibly also from the East European V. ambigua (2n = 40) during its evolutionary history. Geographical differentiation, presumably relatively recent and post-glacial, was evident in V. hirta. Variation occurred also between and within V. odorata populations, most likely a consequence of independent introductions by man. No variation was observed in V. collina or in V. suavis. A key to the Norwegian species of subsection Viola and their primary hybrids based on morphological characters is provided in Flora Nordica note No. 26.

• Marcussen, Thomas & Borgen, Liv (2000). Allozymic variation and relationships within Viola subsection Viola (Violaceae). Plant Systematics and Evolution. ISSN 0378-2697. 223, p. 29–57. Show summary

  Allozyme markers from ten European taxa of Viola subsection Viola suggests that this group is allotetraploid, based on x=5. All taxa had distinct multilocus phenotypes except V. alba sspp. alba and scotophylla, which were identical and different from ssp. dehnhardtii. Variation was consistently higher in Mediterranean populations than in North European ones. Hybridisation seems extensive but putative F1 hybrids were distinctly less fertile than the parental species. Nevertheless, increased fertility in later-generation hybrids and shared band patterns among taxa indicate an important role of hybridisation and introgression in past and present evolution within the subsection. The octoploid V. ambigua shows affinity to V. hirta (tetraploid). The octoploid V. suavis probably originated from V. pyrenaica and other unidentified tetraploids, and high variability suggests polytopy or even polyphyly. The stoloniferous condition (series Flagellatae) seems to be primitive in the subsection but the reduction of stolons (series Eflagellatae) may have originated multiple times.

• Marcussen, Thomas & Nordal, Inger (1998). Viola suavis, a new species in the Nordic flora, with analyses of the relation to other species in the subsection Viola (Violaceae). Nordic Journal of Botany (NJB). ISSN 0107-055X. 18(2), p. 221–237. Show summary

  Evidence from cytology, enzyme markers and morphometry suggests that a species of Viola (Violaceae) collected in southeastern Norway should be referred to V. suavis, although differing in some phenotypic traits. Viola suavis is not previously known from the Nordic countries, but must now be regarded as an established member of the Norwegian flora. It was probably introduced more than a century ago, providing an interesting analogy to the situation of V. alba in Öland (Sweden). Thus, it seems like human activity has played a role for expanding the distribution areas of several of the species within Viola (V. alba, V. hirta, V. odorata and V. suavis). Electrophoretic evidence showed that the basal chromosome number of the subsection is x=5. Viola suavis is allo-octoploid, and closely related tetraploid taxa were easily reconised. However, it is difficult to trace its origin back to lower-ploid ancestors, and it seems likely that the complex may have contained extinct taxa with other allelic combinations that would better explain the origin of V. suavis.

• Marcussen, Thomas & Nordal, Inger (1998). Viola suavis - a new species in the Nordic flora - with comparisons with other species in the subsection Viola. Nordic Journal of Botany (NJB). ISSN 0107-055X. 18, p. 221–237.

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• Marcussen, Thomas & Jakobsen, Kjetill Sigurd (2023). En nasjonal dugnad for å kartlegge genomene til alle artene i Norge – EBP-Nor. Biolog. ISSN 0801-0722. 41(1), p. 6–12.
• Schubert, Marian; Grønvold, Lars; Marcussen, Thomas; Meseguer, Andrea; Sandve, Simen Rød & Hvidsten, Torgeir Rhoden [Show all 7 contributors for this article] (2019). Evolution of tolerance to temperate climates in the grass subfamily Pooideae.
• Fjellheim, Siri; Marcussen, Thomas; Schubert, Marian & Meseguer, Andrea (2018). Evolution of adaptations to temperate climate in the grass subfamily Pooideae .
• Vivian-Smith, Adam; Sønstebø, Jørn Henrik; Marcussen, Thomas; Uleberg, Eivind; Graham, Julie & Sønsteby, Anita [Show all 7 contributors for this article] (2015). Genomic Survey Sequences and the Structure of the Rubus chamaemorus L. and Rubus arcticus L. Genomes As Determined By Double Digest Restriction Associated Digest-(ddRAD) Tags.
• Marcussen, Thomas; Nordal, Inger & Jonsell, Bengt (2001). Phylogeography in the Viola rupestris and V. riviniana complexes ¿ a preliminary study. Show summary

  As widely distributed, Viola rupestris has probably recolonised the deglaci-ated areas of Europe from numerous refugia. Viola riviniana, on the other hand, with its relatively restricted distribution and notable absence from the Caucasus, seems to have recolonised Europe from considerably fewer refugia. There is evidence that the alloploid Viola riviniana has been substantially affected by postglacial introgression from one of its parental species, V. reichenbachiana. More generally, introgression from parental taxa is an important, if not crucial, factor increasing the variability of (nascent) allo-ploids.

• Marcussen, Thomas (2000). Phylogeography in Viola elucidated by allozymes. Show summary

  The three taxa Viola alba, V. odorata, and V. suavis are closely related. In spite of much similar present distributions (South Europe and West Asia), allozymic analyses have revealed their phylogeographical histories to be widely dissimilar. The Viola alba complex is usually divided in several more or less geographical races. The mostly white-flowered morphs from Central Europe (ssp. alba and ssp. scotophylla) and the purple-flowered Caucasian morph ("V. besseri") proved identical and must all be included in ssp. alba. The Mediterranean morph (ssp. dehnhardtii) is, however, distinct. Higher levels of variation in the Caucasus indicate recruitment of European ssp. alba from glacial refuges in this region. The Mediterranean ssp. dehnhardtii was also variable, suggesting a separate refuge for this taxon. The transition zone between the two subspecies across southern Europe may be considered a persistent hybrid zone. Viola odorata. Allozymes suggested that the European and Caucasian materials of this species were recruited from different refugia. The Macaronesian V. maderensis was not recognised, and any original geographical patterns within Europe may have been homogenised by extensive cultivation. Viola suavis is critical and has been divided into numerous morphs, which are not supported by allozymes nor by chromosome counts. However, the investigated materials from Europe and the Caucasus proved widely different, both in allozymic composition and in ploidal levels (2n=40 vs. 2n=20). Conclusively, these represent two quite distinct species: Either (i) the Caucasian materials belong to the true V. suavis (type from Kiew) and the European taxon must take the newer name V. sepincola, or (ii) they represent a new and yet undescribed species.

• Nordal, Inger; Marcussen, Thomas & Berg, Tore (1999). Fagerfiol Viola suavis - ny, men likevel gammel i norsk flora! Blyttia : Norsk botanisk forenings tidsskrift. ISSN 0006-5269. 57(3), p. 109–116. Show summary

  This paper is a popular presentation of data from Marcussen & Nordal (1998) and previously unpublished data on Viola suavis M. Bieb. from France. The identity of a Viola population from SE Norwat (Kragerø) is established by data from isoenzymes, morphometry and chromosome number, which points to V. suavis. The Norwegian name"fagerfiol" is proposed for V. suavis. The species, which was introduced to Norway more than 100 years ago, is fully naturalized. It grows in close proximity to V. hirta and V. odorata without any signs of hybridization, even though such hybrids are reproted from Central Europe.

• Henriksen, Olaf; Corey, Linda A.; Pellock, John M.; Berg, Kåre; Solaas, Marit Hornberg & Refsland, Grethe B. [Show all 7 contributors for this article] (1999). The roleof genetics in epilepsy is demonstrated through studies of Norwegian and Virginian twins.
• Marcussen, Thomas & Borgen, Liv (1999). Variation and relationships within Viola, subsect. Viola.
• Marcussen, Thomas (1998). Viola L. subsection Viola: Variation, hybridization, and relationships among taxa. Biologisk institutt, UiO. Show summary

  Morphological and allozyme (AAT, AMP, GPI, IDH, PGM, SKD) variation was investigated from a total of 64 European populations (547 individuals) of Viola alba Bess. (2n=20), V. ambigua Waldst. & Kit. (2n=40), V. collina (2n=20), V. hirta L. (2n=20), V. jaubertiana Marès & Vigin. (2n=20), V. odorata L. (2n=20), V. suavis M.Bieb. (2n=40), and several hybrid generations. Allozymes revealed that the 2n=20 taxa should be regarded as tetraploids, hence a new basic chromosome number (x=5) is revealed for Section Viola. Most taxa were enzymatically distinct and only little intraspeciefic variation was revealed. However, high amounts of morphological variation and regoional differentiation was found , especially in V. alba, V. hirta, and V. suavis. Multiple introductions of V. odorata into southern Norway is suggested. Considerable morphological and enzymatical overlap was found between V. alba ssp. alba and ssp. scotophylla, which seem to differ only in pigmentation. Ssp. dehnhardtii, on the other hand, was distinct. Viola jaubertiana seemed isolated from the other European species, at least morphologically, and also differed slightly from descriptions from the type locality. Hybrids were generally intermediate betwen the parental species, displaying low fertility and variable amounts of heterosis. Whereas stabilized individuals of V. alba x odorata and V. collina x hirta were found in the European material, hybrids of further generations could not be positively identified in the Norwegian populations. However, several F2 and F3 hybrid generations could be raised. Hybrids of further generations generally displayed reduced heterozygosity accompanied by increased fertility. Reticulation seemed to have played a certain role in the past evolution of subsection Viola. A large proportion of alleles were mosaically shared among taxa, indicating hybrid satbilization at the 2n=20 level. Viola ambigua and V. suavis were best interpreted as allo-octoploids having originated from tetraploid taxa. Their parentages were, however, difficult to trace, but V. ambigua seemed particularly closely related to V. hirta, and V. suavis to both V. odorata, V. collina, and somewhat to V. jaubertiana.

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