Citation Classics are key papers in a research field. They are characterised by having citations to them above a threshold number. Those who know me, even just a little, will know that I’m fascinated by such papers. This fascination began as a student with my pleasure in reading the personal recollections of authors of Citation Classics that were published in Current Contents between 1977 and 1993.
Recently, I came across a paper by MA Martínez, M Herrera, J López-Gijón and E Herrera-Viedma describing a simple method to identify Citation Classics using the Web of Science database, and I thought I would try it.
I decided to identify the Citation Classics that were published during my ‘tenured’ scientific career in my research field. So, on 14th January 2018, I searched the Web of Science Core Collection using the subject “SU=(Plant Sciences)” for the period 1992-2017. This search yielded 548,066 papers with an H-index of 517 (Figure 1). The definition of the H-index is the largest number of papers in the search (n) that have been cited by other papers at least n times. Thus, by the definition of Martínez and colleagues, there were 517 H-Classics in my search and the threshold for a Citation Classic using this criterion was 517 citations.
My list of Citation Classics included 275 reviews, 235 articles (of which one had been retracted) and 7 other articles. As might be expected, the ten most cited papers were either seminal reviews or described widely-applied methods. In order of their citation abundance they were:
- Clough SJ, Bent AF (1998) Floral dip: a simplified method for Agrobacterium-mediated transformation of Arabidopsis thaliana. Plant Journal 16, 735-743. [10,111 citations]
- Apel K, Hirt H (2004) Reactive oxygen species: Metabolism, oxidative stress, and signal transduction. Annual Review of Plant Biology 55, 373-399. [4,262 citations]
- Mittler R (2002) Oxidative stress, antioxidants and stress tolerance. Trends in Plant Science 7, 405-410. [4,067 citations]
- Maxwell K, Johnson GN (2000) Chlorophyll fluorescence – a practical guide. Journal of Experimental Botany 51, 659-668. [3,443 citations]
- Barthlott W, Neinhuis C (1997) Purity of the sacred lotus, or escape from contamination in biological surfaces. Planta 202, 1-8. [3,153 citations]
- Munns R, Tester M (2008) Mechanisms of salinity tolerance. Annual Review of Plant Biology 59, 651-681. [3,047 citations]
- Noctor G, Foyer CH (1998) Ascorbate and glutathione: Keeping active oxygen under control. Annual Review of Plant Physiology and Plant Molecular Biology 49, 249-279. [2,970 citations]
- Zhu JK (2002) Salt and drought stress signal transduction in plants. Annual Review of Plant Biology 53, 247-273. [2,481 citations]
- Angiosperm Phylogeny Group (2009) An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III. Botanical Journal of The Linnean Society 161, 105-121. [2,406 citations]
- Dixon RA, Paiva NL (1995) Stress-induced phenylpropanoid metabolism. Plant Cell 7, 1085-1097. [2,347 citations]
What surprised me most was, with the exception of the Angiosperm Phylogeny Group (APG III), they were all single or two-author papers. It was also interesting, following the discussion of the recent paper by Courchamp and Bradshaw (Nature Ecology & Evolution 2, 395–401, 2018) “100 Articles Every Ecologist Should Read” which listed only two articles with female first authors, that three of the top ten contemporary Citation Classics in Plant Sciences had female first authors (Kate Maxwell, Rana Munns, and Birgitta Bremer for APG III). This might reflect the contrasting methods of compiling the lists, the different subject areas, or the periods represented by each list.
How long does it take to become a Citation Classic in Plant Sciences?
I then calculated the number of Citation Classics in each year to answer the naïve question: How long does it take to become a Citation Classic in Plant Sciences? The most recent papers on my list were from 2012 and the number per year gradually increased as one went back in time to about 2004 after which it became roughly constant (Figure 2A). In doing this analysis I noticed that between 1992 and 2004 the average number of Citation Classics was about 0.2% of the total number of papers published each year, or 1 in 500 papers (Figure 2B). This is one fifth of the 1% of papers that are designated “Highly Cited” on Web of Science.
Finally, on a purely personal note, I was pleased that two reviews I co-authored: White PJ, Broadley MR (2003) Calcium in plants. Annals of Botany 92, 487-511. [718 citations] and Broadley MR, White PJ, Hammond JP, Zelko I, Lux A (2007) Zinc in plants. New Phytologist 173, 677-702. [605 citations] appeared at #241 and #349 in the ranked list.
Should anyone wish to know more about the authors, journals or organisations represented in the 517 Citation Classics in Plant Sciences, perhaps I’ll disclose these in another blog article.