I find the flavor of cooked Dryopteris dilatata (broad buckler fern) rhizome, to be good, not excellent. It's a bit like sweet potato as reported by Turner et al (1) but not quite as good or sweet I'd say, I did not think it was much like coconut as reported. It also reminded me of salmon a little, I don't think it was just that it is the same color as salmon. I've only tried one rhizome, I think a taste could well be acquired for it.
I harvested the rhizome in late autumn (in New Zealand), the plant still had leaves, apparently Dryopteris species are usually harvested in late autumn or early spring before the leaves have developed (2) it's possible the time of harvest affects quality.
Turner & co report Dryopteris rhizomes are boiled for a long time until tender. I boiled them for one hour, they were quite soft, probably they could be cooked for shorter periods I think.
It is worth noting that all the reports of edibility for this species come form North America/Canada, yet all modern authorities I can find say this plant is not native to the Americas, rather Europe and Asia (3). Experts note how Dryopteris dilatata is very hard to distinguish from several American native Drypoteris such as Dryopteris expansa (definitely used as food) and is closely related, if not a cross with this plant and Dryopteris intermedia (4). It is not at all clear to me that Dryopteris dilatata is the species described as edible in the ethnobotanical and historical accounts, though I found the taste basically matches the description.
Toxicity is also an issue. The related male fern, Dryopteris filix-mas, is extremely toxic raw (5), though reportedly was eaten cooked by American Indians (6). Other Dryopteris have only been found to contain the milder toxin thiaminase (7) which is destroyed by five minutes boiling (8). There are no reports of poisoning from Dryopteris dilatata in the International Poisonous Plants Checklist. An Evidence-Based Reference (2008), which includes livestock poisoning, there are many for Dryopteris filix-mas. I noticed no ill effects after ingesting one cooked rhizome of dilatata.
It is probably not significant that there is no ethnobotanical record of Dryopteris dilatata being eaten outside of America. Most if not all of the many Dryopteris eaten by American Indians are also present all over Europe and Asia but are not recorded as having been used as food outside of America.
I would say this very neglected crop is one of the best for growing in heavy shade/understory (9) but have not yet tried growing it in these conditions here in New Zealand. The rhizome is also basically on the surface so is easy to harvest, requiring little or no digging. Peeling the rhizome, as the American Indians do (or did), is a bit fiddly. The plant is clump forming so propagates itself to an extent, it has gone wild in parts of New Zealand so may also self sow. It is reportedly vigorous (10) so it sounds like it may somehow be reasonably productive even with very little direct sunlight, although Lukasz Luczaj says fern rhizomes take many years to reach full size (11).
References:
1) EDIBLE WOOD FERN ROOTSTOCKS OF WESTERN NORTH AMERICA: SOLVING AN ETHNOBOTANICAL PUZZLE. N Turner et al J. Ethnobiol. 12(1):1-34 Summer 1992
2) Edible and Medicinal Plants of Canada. MacKinnon et al. 2009.
3) e.g., Kew Gardens https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:30117034-2
4) Unraveling reliculate evolution in North America Dryopteris (Dryopteridacea). E Sessa, E Zimmer, G Givish. BMC Evolutionary Biology 12, 2012
DRYOPTERIS DILATATA (HOFFM.) A. GRAY IN NORTH AMERICA Donald M. Britton Rhodora
5) https://www.sciencedirect.com/topics/immunology-and-microbiology/dryopteris
6) Native American Food Plants. An ethnobotanical dictionary. D Moerman. 2010.
7) https://pfaf.org/user/Plant.aspx?LatinName=Dryopteris+dilatata#:~:text=Dryopteris%20dilatata%20is%20a%20FERN,ripen%20from%20July%20to%20September.
8) https://spo.nmfs.noaa.gov/sites/default/files/pdf-content/mfr2883.pdf
9) "may sometimes be dominant or the only species in deep shade" Biological Flora of the British Isles: Dryopteris carthusiana, D. diatata and D. expansa. K Runk et al. 2012
10) https://plants.ces.ncsu.edu/plants/dryopteris-dilatata/#:~:text=Broad%20Wood%20Fern%20is%20a,tall%20with%20a%20similar%20spread.
11) Lukasz Luczaj. Edible Ferns of the World. 2022. (page 100).
