Etrog sliced

Do we need evidence in books about plants?

Without a source are facts really facts, or just factoids?

Etrog sliced
Image: Canva.

We rightly require evidence – usually appropriate reference to the work of others (e.g. Bart Penders (2018) PLoS Comput Biol 14(4): e1006036) – to support arguments or claims made in scientific articles. We also request that our students provide references to support statements made in their essays or practical write-ups, etc. – both as part of their apprenticeship in learning the art and craft of scientific writing, and to avoid a charge of plagiarism. Whether in an increasingly sceptical world or not, we should always ask for proof, or at least, appropriate evidence, to support assertions made by others. We shouldn’t just accept facts ‘on trust’ – however well-meaning or otherwise worthy we may consider the source to be.* So much for traditional science writing, what about non-fiction books, particularly those dealing with plants?

I’ve had the good fortune to read many factual botanical books and share my musings on the Botany One site (e.g. here, here, and here). With my botany teaching hat on I usually consider the educational value of those books. As a result of that scrutiny I’ve noticed a trend that needs to be aired, and maybe challenged, but certainly discussed. I’ll use The Story of Trees by Kevin Hobbs and David West as the example. Not because it’s the worst ‘offender’ of the issue I raise, but purely because it’s the most recent book I’ve appraised and so is freshest in my mind.

The Story of Trees is a factual book – about trees and how they’ve changed the way we live – but does not include any references. Why should it? The book does not claim to be an academic text, and is probably aimed at the intelligent lay reader, so there’s probably no expectation that it should include any references. Furthermore, incorporation of references in-text would interrupt any narrative flow the authors seek to maintain and spoil the reading experience.

But, The Story of Trees is jam-packed full of statements [“facts”] about trees and human exploitation of, and interaction with, them. Being so fact-filled makes it a really useful book and I’ll have great fun incorporating the odd snippet of tree ethnobotany into my own writings and talks. However, the absence of any sources for the statements made – lack of any in-text references aside, it doesn’t have any foot-notes, list(s) of sources used by the authors, nor any suggestions of further reading – not only makes it difficult for interested readers to pursue their own investigations into the information provided, but also means that they have to take the authors’ word for the information contained within. Whilst I have no reason to doubt the good intentions of the authors in neither wishing nor intending to mislead or misinform the readers, this creates an issue…

The issue in question is highlighted by the etymology of the binomial Citrus medica, the scientific name of the citron. On p. 83 of The Story of Trees, the authors state that the specific epithet ‘medica’ refers to the fruit’s medicinal claims and uses – which are many (e.g. here, here, and here). And that assertion seems reasonable on the basis that medica is similar to words such as ‘medicine’, a word in Modern English derived “directly from the Latin medicina, which means “the healing art, medicine; a remedy””, ‘medical’, from the Latin word medicus meaning a “physician, surgeon, medical man”, and the “Medieval Latin medicālis, equivalent to Latin medic(us) medical (adj.), physician (noun)”.

However, in his monograph devoted to the etrog – another common name for the fruit of C. medica – author David Moster is quite clear [on p. 27 of his book] that medica relates to the Greek word for Media, an “ancient country of northwestern Iran, generally corresponding to the modern regions of Azerbaijan, Kurdistan, and parts of Kermanshah”. Media is one of the regions associated with the journey of etrog to the Holy Land, which ancient connection is acknowledged in Median apple, a common name in antiquity for the fruit of C. medica.

Seemingly anticipating the surprise that may be occasioned by that revelation, Moster specifically states that it is a common misunderstanding that medica relates to the fruit’s medical qualities [also on p. 27 of his book]. Is this a solid piece of evidence in favour of the geographical interpretation, or merely a strongly-held view by the author of Etrog? In support of Moster’s statement, several sources are cited in his book – in-text on p. 27 – which could be consulted if required. So, on the one hand we have Hobbs and West’s claim, which is unsubstantiated** and, on the other, there’s Moster’s evidence-based – and contradictory – explanation.

As a ‘seeker after truth’ – nowadays as a would-be botanical educator and plant science communicator, and in former careers as a financial auditor and research scientist – I was taught that, if two pieces of evidence contradict each other, you need to seek other, additional, evidence to resolve the matter because both cannot be right. This I duly did and the only source I could readily uncover – by Googling*** – was the OxfordPlants400 item on the citron which stated “Carolus Linnaeus’s use of ‘medica’ in the species epithet does not refer to citron’s medicinal use but rather its association with the classical empires of Persia and Media”. Unfortunately, the ultimate source of that ‘fact’ is not clear. Although that blog item lists two references as further reading, neither is explicitly cited as the source of the classical empire origin of the specific epithet. However, inspired by that further reading, some more internet searching unearthed two more sources relevant to untangling the etymological conundrum.

Dafna Langgut proposed that “The word medica in the Latin name (Citrus medica) may also suggest its Persian (Median) origin rather than its use for medical purposes” (p. 816) (HortScience 52: 814-822, 2017;). David Mabberley, on the other hand, muddies the water somewhat in saying that “The naming of the citron as Citrus medica by Linnaeus perhaps indicates the early recognition of the pharmaceutical importance of the genus, though the epithet may refer to the Medes [i.e. the plant’s Median connection – see above], or, of course, to both” (p. 491) (Blumea 49: 481-498, 2004;).

The result of my internet interrogation is two and a half sources that substantiate Moster’s interpretation, and half a source supporting Hobbs and West’s. Although the jury is probably still out, the balance of probabilities favours the Moster – geographical – interpretation of the meaning of medica, which is contrary to the one stated in The Story of Trees.

So, with two different interpretations of the meaning of ‘medica’, which is correct? Or, are both wrong, and there’s a third – as yet unearthed – correct one? Had I not been aware of the ‘Moster interpretation’ before reading The Story of Trees, I’d have been happy to accept Hobbs and West’s statement as fact. I suspect that will be the case for the majority of the readers of that book. And, had a reference been supplied for their medicinal interpretation, we’d at least have that as support for the statement – however contentious Hobbs and West’s interpretation has turned out to be – and I may not have done any digging of my own to try and establish the truth.

An important question from this is: Where does the onus lie regarding the veracity of statements [see the item by Emma Copley Eisenberg on this point] in non-fiction botany (and other science subjects) books? Must it rely on the vigilance of sceptical readers who won’t necessarily accept something as true just because it’s in a book? Should we insist on authors revealing their sources in the book? After all, published science facts are matters of public record; they’re not secrets and are meant to be shared; they’re not privileged information from confidential conversations with individuals whose identity needs to be protected as may be the case with investigative journalism. I have sympathy with the view that references in-text might appear be too heavy-going for non-academic books intended for a general audience. After all, one doesn’t wish to turn readers away! But, if those books are to be accepted as factually correct (or at least accurate as far as is supported by the source supplied, but accepting that alternative interpretations supported by other sources might exist…), shouldn’t we require an indication of the author’s sources to be included somewhere in the book?**** Maybe we need two versions of the book – the one that’s published in a format suitable for the intended audience, and another with full inclusion of evidence? Even then, can one accept the references supplied as being the last word on the truth of what’s written?

Is this really a problem? Am I over-reacting? Yes; and I don’t think so (respectively). As highlighted in this item regarding Citrus medica, without any mention of sources to refer to to check the accuracy of published statements – or the author(s)’ own interpretations thereof [another potential minefield of misunderstanding, misinformation, and misdirection….] – inaccuracies can be perpetuated but accepted as correct that which may not be. If we cherish scientific literacy (and we all should!), this is a problem that needs to be acknowledged, and addressed. If authors don’t provide evidence, how can we as would-be educators demand evidence-based work from our students?

At the risk of making this blog item too long, I feel I should also mention plant science textbooks here because they share my concerns highlighted above for non-fiction books. Arguably, because these fact-based, academic books are specifically intended to inform and provide the knowledge base for the next generation of Botanists, they are even more problematic than more populist books. In my experience, many – most? – Botany textbooks do not include in-text references to support the facts they contain, e.g. Buchanan et al’s Biochemistry and Molecular Biology of Plants, 2e (but does have a chapter-by-chapter list of further reading at the end of the book), Taiz et al’s Plant Physiology and Development, 6e (but does have a list of suggested reading at the end of each chapter), Evert & Eichhorn’s Raven Biology of Plants, 8e (but which includes an end-of-book listing of chapter-by-chapter suggestions for further reading), Chrispeels & Gepts’ Plants, Genes & Agriculture (which has suggestions of further reading at the end of each chapter), Mauseth’s Botany: An Introduction to Plant Biology, 6e (and which doesn’t contain any suggestions of further reading either), and Jones et al’s The Molecular Life of Plants (which is also devoid of any suggested reading).

Whether containing suggestions of ‘further reading’ or not, without in-text references – the mainstay of evidence-based science writing – how is the veracity of a textbook’s content to be judged? Although much of the same information is provided in many texts from different authors and publishers, that doesn’t necessarily make it correct (nor does it necessarily make it wrong, but it is unsupported and unevidenced). And, if not correct, there is a risk of the uncritical repetition – and acceptance – of incorrect information. If that continues for long enough, and without challenge, these statements become accepted as ‘fact’.

Where should the line be drawn? Whilst we probably prefer the idea of readable narrative, it shouldn’t be at the expense of evidence-based, accuracy. Maybe we should treat such texts in the same way we might advise our students to use a page on Wikipedia, as a good starting point but with an important need to go to the original source(s) – for a proper, defensible, evidence-based statement. Without that, what assurance does the reader have that each fact has been checked, is evidence-based, and as correct as the authors can make it? Yes, I’m aware that this legitimate querying risks upsetting those involved in the botany textbook market, but I believe that this matter is important and needs to be aired and discussed. Shouldn’t books written by plant scientists lead by example in showing the best practice of the scientific writing we demand of our students?

* Surely, nobody of any integrity wants to be accused of “ipsedixitism”?

** Irritatingly, an article by ‘JTA’, that appears to be a review of Moster’s book, clouds the issue by presenting this statement; “Eventually, the fruit made its way from East Asia to India, where it was used as a remedy for gastrointestinal issues (hence its Latin name, Citrus medica) and appeared in iconography as a fertility symbol”. Although that article doesn’t cite a source for this statement – and contradicts the information in the book it appears to review(!), it’s arguably a source that could be cited to support Hobbs and West’s contention…

*** The only other source found readily relating to a Google search of ‘etymology of citrus medica’ was the Wikipedia page for citron, which article’s Etymology section states that “The fruit’s English name “citron” derives ultimately from Latin, citrus, which is also the origin of the genus name…”. Not quite the full etymological derivation one required to help resolve the matter in hand.

**** A related consideration is how far back in the literature one should go to obtain the original source of a statement in a scientific paper – something highlighted in a blog item looking at the role of root hairs. But, maybe that’s a ‘can of worms’ best left to another day..?

Nigel Chaffey

I am a botanist and former Senior Lecturer in Botany at Bath Spa University (Bath, near Bristol, UK). As News Editor for the Annals of Botany I contributed the monthly Plant Cuttings column to that august international botanical organ - and to Botany One - for almost 10 years. I am now a freelance plant science communicator and Visiting Research Fellow at Bath Spa University. I continue to share my Cuttingsesque items - and appraisals of books with a plant focus - with a plant-curious audience. In that guise my main goal is to inform (hopefully, in an educational, and entertaining way) others about plants and plant-people interactions, and thereby improve humankind's botanical literacy. Happy to be contacted to discuss potential writing - or talking - projects and opportunities.
[ORCID: 0000-0002-4231-9082]


  • While I agree with your overall thesis regarding the need for reference citations in academic publications, I think you chose a really bad example to illustrate the point.
    I can’t be certain of the origin of Citrus medica, however I support the author’s interpretation on the basis that medica is a widely used term in classical nomenclature, there being no doubt that material medica is a reference to a list of medicines, traditionally mainly derived from plant sources. The term was widely used in the past and is still in use today (I teach a materia medica course currently).
    I admit to not being aware of media as a name for Persia, but if this is the case surely the taxonomic authority would have named the plant Citrus media.
    That’s my take on it anyway, regards Andrew

    • Apologies for a spelling error in my post. Material medica should read material medica, probably an autocorrect gone wrong.

    • Dear Dr Pengelly,

      Thank you for taking the time and trouble to comment on this blog item (and also for your two follow-up comments). It’s always to nice to know that people read my work and are sufficiently moved to respond to it.

      I’m pleased you agree with the need for evidence in respect of plant facts.

      No single example is probably perfect as an illustration of the issues that can arise in the absence of an appropriate citation. Your comments about a medical derivation are noted. However, another commentator has been in touch with me and provided two additional pieces of evidence in support of the geographical interpretation of the scientific name of etrog.

      The intricacies of scientific terminology are nevertheless a fascinating area of study – and can clearly provide fuel for interesting debate.


      Nigel Chaffey

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