I've found Polygontum multiflorum (Common Solomon's Seal) is exceptionally tolerant of deep shade. Here it is growing with only a little dappled light in the understory of the New Zealand native tree Mahoe, Melicytus ramiflorus (very common in Wellington suburbs where native bush has been allowed to recover). It is possible there is slightly more indirect light available to this plant than in some dense Mahoe groves but you can see in the background nothing else is growing naturally nearby. This plant is also on a very steep slope, almost vertical.
The young shoots are edible (1) with a pleasant taste. The shoots are available in spring, it is not a very productive crop, you'd need a lot of plants for a good feed. Couplan says the roots are fibrous but edible starch can be extracted from them, requiring cooking to make them safe to eat and have also been used in making bread (2). Another reports says they are eaten raw (3), Moerman (4) and Gibbons (5) say the rhizomes can be cooked and eaten without mention of fibers or toxicity, I've not tried them yet.
The rhizomes of many other shade loving Polygonatum species are eaten in China with little or no preparation (6). Some are sold in Chinese supermarkets and online, including those of Polygonatum odoratum, which is widely available as an ornamental in the West.
1. https://pfaf.org/user/Plant.aspx?LatinName=Polygonatum+multiflorum
2. Couplan F. The Encyclopedia of Edible Plants of North America. Nature's Green Feast. 1998.
3. Wild edible plant resources of the Lobha Range of Kedarnath Forest Division (KDF), Garwhal Himalaya, India. Radha et al. International Journal of biological sciences V2(11) 2013
4. Moerman D.E. Native American Food Plants. An Ethnobotanical Dictionary. 2010.
5. Gibbons. E. & Tucker G. Euell Gibbons Handbook of Edible Wild Plants. 1979.
6. e.g., Ethnobotanical review of food uses of Polyonatum (Convallariaceae) in China Wujisguleng Wujisguleng, Yujing Liu, Chunlin Long Vol 81, No 4 (2012) > Wujisguleng
