We are in the process of writing to the plant portraits forthcoming book on forest gardening and it's set position with a small post about source criticism. At the beginning of work on the book we used much of the extensive database Plants for a Future (PFAF). It is very good in many ways but what we realized is that one should be careful, at least in the edibility of less known plants halesia carolina (Halesia carolina), Siberian ärtbuske (Caragana arborescens), idegransplommon (Cephalotaxus spp.) and flower chestnut (Xanthoceras sorbifolium). All these I have written about on this blog and had the aforementioned database and Martin Crawfords fantastic book Creating a Forest Garden [1] as a source of information about their edibility.

If we take as an example snödroppsträdet, writes PFAF that it is possible to eat fruits. The sources that support this, it is enormously comprehensive encyclopedia Cornucopia II [2] och Sturtevant’s Edible Plants of the World [3]. Cornucopia II itself refers back to Sturtevant's and another book called Edible Wild Plants of Eastern North America [4]. What do Sturtevant's time, a book that came out 1919 and that is a summary of the work that was done mainly in the 1870s? Already, so here it is: ”The ripe fruit is eaten by some people and when green is sometimes made into a pickle."No source, no further information. Does that sound like a plant description you would trust? The last straw is when the book of wild plants in the eastern US. There is halesia carolina under the category of "thirst quencher" with the description that you can "move around the fruit in the mouth for its sourness ". Nothing more and certainly nothing about it would be a good idea to chew on the fruit or swallow it. In other words, PFAF based their information on the edibility of our eyes very dubious information and a rather sloppy source management.

Snödroppsträdets fruit tastes like cucumber salad, but it is to our knowledge no evidence that they really are harmless.

Unfortunately, it seems to be generally a bad habit in this context, citing secondary sources without going back to the original source. We can take another example, The much publicized and acclaimed Siberian ärtbusken (Caragana arborescens). The I myself have planted dozens of copies of the order to reap a multi-year alternative to peas or lentils. The plant is mentioned so often in the literature that I never even questioned its edibility. Specifies PFAF the already mentioned Sturtevant's and Cornucopia II as the main sources. Also mentions another source, Tanaka’s Cyclopedia of Edible Plants of the World från 1976 [5], a standard work cited constantly, but that is almost impossible to come by. We made ourselves the trouble to travel all the way to Uppsala to browse Sweden's only publicly available copy of this mythical book. It turns out that it is constructed in much the same way that Cornucopia II, with very brief information about each plant and references to where the information is coming from. * And what we find? Already, a reference to the old Sturtevant's and other reference books that we did not know already, boken Dictionary of Economic Plants av J. Uphof from 1968 [6]. Where the latter get their information from being shrouded in gloom, but where it is possible to read the ”Young pods are eaten as a vegetable in some parts of Siberia.”, while Sturtevant's writing often quoted sentence ” The seeds are of culinary value but are used particularly for feeding poultry.”. No further source specified in any of the books. PFAF should therefore not be quoted Tanaka in this context, but only Uphof and Sturtevant.

Sibirisk ärtbuske – edible or not?

To verify this kind of shaky references we use Google Scholar, which is a search engine for scientific publications. There was not a single reference to snödroppsträdets edibility. The same applies Siberian ärtbuske, entirely surprising seems to be an almost unexplored crop. Likewise with the flower chestnut. Certainly, one can extract an edible oil from the, but not without a lot of processing. Most of the publications we found about its potential as a crop for biofuel in dry climates. The "pretty sweet" taste quoted in Cornucopia II, we can not confirm our own experience. The nuts we tasted was rather bitter and evoked in me some nausea, which confirmed that the plant belongs to the family Sapindaceae, characterized by fleshy saponininnehåll. And idegramsplommon examined today most of its active substances against cancer, not as edible crops, although we found many quotations in the botanical encyclopaedia about the fruit of Cephalotaxus harringtonia was. nana would be edible [5-7]. In our experience gives fruits an unpleasant taste of resin that etch themselves to the whole mouth, and that does not go away for several hours.

Blomsterkastanj (Xanthoceras sorbifolium) may become a biofuel crop in dry, chilly climate, but if it is suitable for human consumption is extremely uncertain.

Since our after increases among the scientific publications produced no fruit, we contacted including even the experts Stephen Barstow, Eric Toensmeier and Martin Crawford, but none of them had no other sources available. The lack of scientific research on the plant edibility need not of course mean that they are not edible. We hope for more research on these crops. Until we dare not recommend them as food crops and have put them into our “blacklist” in the book of plants we opted out on purpose.

Do you know more about these plants than we? Please contact us at skogstradgard@gmail.com!

* Unfortunately a large part of the references in Tanaka only in Japanese and many of them are from the early 1900s.


[1] Crawford, M., Creating a forest garden : working with nature to grow edible crops. Totnes: Green Books, 2010.
[2] Facciola, S., Cornucopia II: A Source Book of Edible Plants. Kampong Publications, 1998.
[3] Hedrick, U. P., Cyclopedia of Hardy Fruits. 1938.
[4] Fernald, M.L., A.C. Kinsey, and R.C. Rollins, Edible wild plants of eastern North America. New York: Dover Publications, 1996.
[5] Tanaka, T. and S. Nakao, Tanaka’s Cyclopedia of Edible Plants of the World Cyclopedia of Edible Plants of the World. Yugaku-sha, Tokyo, 1976.
[6] Uphof, J.C.T., Dictionary of economic plants. Dehra Dun, India; Ruggell, Germany; Koenigstein, Germany: Bishen Singh Mahendra Pal Singh ; A.R.G. Gantner ; Koeltz Scientific Books [distributor], 1968.
[7] Huxley, A., M. Griffiths, and S. Royal Horticultural, The new Royal Horticultural Society dictionary of gardening. New York: Grove’s Dictionaries Inc., 1992.

14 thoughts on “Källkritik”

  • Mycket bra artikel! Jag hoppas ni är lika källkritiska när det gäller allt material i boken. Det finns få områden med så mycket myter, tyckande som blir till sanningar och cirkelreferenser som inom trädgårdsodling. Jag ser fram emot att läsa boken när den kommer! : )

    • Tack! Vi gör vårt bästa även med övriga innehållet i boken. Jag tror vi är uppe i 300 vetenskapliga referenser nu och det blev en hel del överraskningar, även trevliga sådana.

  • Tack, thanks, thanks. I can not imagine anything more important for permaculture circuits than to begin to source criticism seriously. Really amazing how much authority many would give to hear-say and how persistent rumors like that can be. Reminds me of the concept of 'Dynamic rechargeable batteries', which has also flourished in permaculture circuits, but that has no scientific basis (and if you go back to the original source, you will find the Robert Kourik who then rejects the notion, but it still continues).

    • Thanks! And, det där med de dynamiska ackumulatorerna är knepigt. Even though the concept is wrong and not accepted, there is a lot of research that supports the basic idea. I wrote about the dynamic accumulators when I had just started blogging and copied basically just what it says in all the books. No source criticism where! But then I also realized that the reality is more complex than that. However, I believe that it is wrong to hook up on the concept of "dynamic accumulator" and believe that it could explain some of the mineral content of different plant leaf. It says nothing about where the minerals come from, Thus, if they are recovered from the topsoil or raised from deeper horizons. I have briefly looked a bit on the concept that "the mineral uplift from deep soil horizons" and gotten a bunch of interesting studies on that. It seems accepted that vegetation changes the mineral distribution in the soil and the minerals that are most lack is enriched in the topsoil where they can quickly recirculated: https://link.springer.com/article/10.1023%2FA%3A1010760720215?LI=true. Some plants seem to be better at redistributing nutrients and apparently they do it because they simply have a greater need of these substances: http://onlinelibrary.wiley.com/doi/10.1890/03-0245/full. I have not been able to find any listings of this, men den här studien tolkar jag som att kanadensiskt gullris kan kicka igång ett ekosystem för att den är mycket bra på att göra mer fosfor tillgängligt i de övre jordlagren: https://link.springer.com/article/10.1007/s00374-005-0039-4. Ännu bättre på det verkar den fruktade parksliden vara: http://www.bioone.org/doi/abs/10.2980/1195-6860(2007)14%5B230:IBFJIT%5D2.0.CO;2. När jag läser sammanfattningen av den här studien får jag en idé att man under kontrollerade former skulle kunna introducera aggressiva invasiva arter för att höja bördigheten på ett ställe, men det kanske är en dum idé: https://link.springer.com/article/10.1007/s00442-008-1054-6. Ser fram emot att borra ner mig mer i det här 🙂

  • Chemical Investigation of Caragana arborescens Shoots (https://www.researchgate.net/publication/243458710_Chemical_Investigation_of_Caragana_arborescens_Shoots) med hänvisning till rysk källa: The decoction of flowering shoots of this species is used in traditional medicine of the Buryatia Republic as an antiinflamatory and immunostimulant.

    The comparation of drought resistance between Caragana species (Caragana arborescens, C. korshinskii, C. microphylla) and two chickpea (Cicer arietinum L.) cultivars https://www.researchgate.net/publication/287190368_The_comparation_of_drought_resistance_between_Caragana_species_Caragana_arborescens_C_korshinskii_C_microphylla_and_two_chickpea_Cicer_arietinum_L_cultivars) Caragana arborescens, C. korshinskii, C. microphylla, deciduous shrubs, commonly found in desert and semi-desert zones, northwestern China, and have important ecological and economic values: including playing a key role in vegetation succession from shifting sand dune to sandy grassland, helping to restore degraded land and serving as supplemental forage for livestock.

    • Mark Shepard nämner ärtbusken i boken Restoration Agriculture, and that there would be scientists in Canada who have shown interest in cultivating varieties that are suitable for larger-scale farming. Guess these researchers (if they are not interested only), can provide information on sources. Mark may also sources? Much knowledge can exist in books, whose information is not necessarily searchable by journal databases.
      daniil Olennikov, cited above by Eva, may also provide more information about the Russian literature?

      Believes in this context that one should also ask what would happen if the need arises entirely conclusive scientific evidence about the healthiness of everything we eat. Meat debate is of course a swamp eg, in which questionable observational studies have found statistically significant, yet minimal risks around carnivorous, as well blown up to “red-meat-kill-you”-alarm even doubtful headlines — while more recent and better studies completely call off the risk of carnivorous. And yet, today we have the debate that we have in Sweden, where meat is usually said to be bad for health. In light of the nature of the phenomenon, it may be a probability that the stamp “EDIBLE and HEALTHY” for Siberian pea, and other untested in Sweden, becomes very difficult to put.

  • Very interesting.

    Moreover, the taste of ass.
    Personally I like a lot to eat leaves of linden (Tilia cordata), but my wife thinks they are no further… A friend like dandelion greens but I think it's far too bitter.

    And so we have the full range of allergies – Hazelnut is both heavenly and deadly…

    What do you most?

  • Nu har det gått 4 years since this post was written. Does anyone know if there has been any research or study of Siberian pea bush that has shed further light on edibility??

    • After I wrote the post, I contacted basically all the analysis companies that I could find online to get a quote on analysis on a bunch of substances that could be found in the fruits of the pea bush.. None of the companies had the opportunity to analyze these particular topics and after that I gave up. To my knowledge, no one else has investigated the issue further either. An alternative might be to contact a university and try to get a degree project that can examine the pea bush from an edibility perspective..

      • Tack för svar och bra förslag Philipp! Jag hörde faktiskt av mig till Martin Weih, professor i växtekologi på SLU, och fick ett väldigt positivt svar 🙂 Han ställer några följdfrågor, som jag inte riktigt kan svara på, eftersom jag än inte själv odlat sibirisk ärtbuske (planerar dock till våren). Kanske kan jag få hjälp med bra svar? 🙂

        Hej Sara!

        Tack för ditt meddelande och ditt spännande förslag på ett exjobb!
        I princip tycker jag att ditt förslag låter riktigt spännande J
        Jag kan mycket väl tänka mig ett exjobb projekt där du försöker odla upp Caragana och gör ett antal analyser.
        Tre frågor som dyker upp hos mig spontant, and which are important for you to succeed:
        1) Is it possible to grow the bush from seeds (or vegetatively e.g.. bulkheads), and how big plants you would get after a couple of weeks of growing in a greenhouse?
        2) Which plant parts would you like to test with regard to content and "edibility"?
        3) How do you want to test "edibility" (I hardly think you want to expose subjects to the plant and then check if they get sick ;-)?

        Looking forward to your answers!
        Best regards,

        • Hej Sara! What a pleasure to contact Martin Weih, by chance he was my supervisor when I did a project work on energy forest on SLU type 2003, but he certainly does not remember. Answers to his questions: It is absolutely possible to grow the pea bush from seed, but it takes a number of years before they yield. Because it's the seeds and the pods (and the flowers) which are possibly edible, I think it would be better to start from existing shrubs. Sjelin's agriculture outside Uppsala has a number of full-grown shrubs on its land, for example. There it would be easy to get enough material. The edibility then needs to be tested in a first step by examining the material on some alkaloids and other compounds. A gross list of what can be found in legumes can be found in the table 1 in this study: https://www.sciencedirect.com/science/article/pii/S0254629913002858. One would need to go through the list and identify the potentially toxic substances and look for them specifically in them “edible” the parts. Feel free to contact me at skogstradgard@gmail.com if you get more answers from Martin. Best regards, Philipp

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