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  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  och Sturtevant’s Edible Plants of the World . Cornucopia II itself refers back to Sturtevant's and another book called Edible Wild Plants of Eastern North America . 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.
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 , 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 . 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.
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.
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 firstname.lastname@example.org!
* Unfortunately a large part of the references in Tanaka only in Japanese and many of them are from the early 1900s.
 Crawford, M., Creating a forest garden : working with nature to grow edible crops. Totnes: Green Books, 2010.
 Facciola, S., Cornucopia II: A Source Book of Edible Plants. Kampong Publications, 1998.
 Hedrick, U. P., Cyclopedia of Hardy Fruits. 1938.
 Fernald, M.L., A.C. Kinsey, and R.C. Rollins, Edible wild plants of eastern North America. New York: Dover Publications, 1996.
 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.
 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.
 Huxley, A., M. Griffiths, and S. Royal Horticultural, The new Royal Horticultural Society dictionary of gardening. New York: Grove’s Dictionaries Inc., 1992.