A nutritional analysis of Hosta is reported in the enclosed open access article from Japan (2017):  “Analysis of essential macro-micro mineral content of twelve Hosta taxa” by Mehraj, Nishimura and Shimasaki.  The good news is that the overall conclusion is that Hostas are  excellent sources of a number of minerals important in human nutrition!
Various Hosta species were collected from the wild as well as from commercial vegetable growers (it is indicated that the Hosta were simply collected from the wild and are not selected otherwise), they were grown for a year in the open before being moved to pots for the analysis.

A few quotes:

“Hosta plant leaves have higher K and P content than that of the other (common) leafy vegetables.”

“We found one species (H.  sieboldii) among the studied 12 species containing 1.15% of Ca, higher than STFC-2015, Japan and all levels found in other studies conducted in different countries for various wild edible plants. Data from our study indicated that H. sieboldii could be an excellent daily diet source of Ca. It appears that Japanese people used to consume this species as a source of calciums. The results of this study indicate that hosta taxa are a good source of Mg and Mn.”

“The Zn content of hosta leaves was higher than other fresh vegetable reported”

“Hosta plant leaves contained higher minerals than that of asparagus. From the results and discussion, it is clear that hosta leaves are a very good dietary source of minerals.”

“H. alismifolia, H. sieboldii, H. nakaiana, H. longissima, H. montana can be considered excellent sources of some minerals and can be recommended for their K, Ca, Fe, P, Mg, Zn content.”  (NB! H. montana is often considered as a synonym or subspecies of H. sieboldiana)

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