Common Name: Zenmai

General Information

Osmunda japonica is a herbaceous fern with an erect, ascending, or shortly creeping rhizome. It produces a cluster of fronds, each up to 150cm tall and 50cm wide[].
The plant is harvested from the wild for local use as a food and sometimes also cultivated[]. The young fronds are commonly sold in local food markets in Korea[].

Known Hazards

Although we have found no reports of toxicity for this species, a number of ferns contain carcinogens so some caution is advisable[].
Many ferns also contain thiaminase, an enzyme that robs the body of its vitamin B complex. In small quantities this enzyme will do no harm to people eating an adequate diet that is rich in vitamin B, though large quantities can cause severe health problems. The enzyme is destroyed by heat or thorough drying, so cooking the plant will remove the thiaminase[].

Botanical References

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Range

E. Asia - Russian Far East, Japan, Korea, central and southern China, Pakistan, northern India, Bhutan, Myanmar, Thailand, Vietnam

Habitat

Moist places all over Japan[, ]. Forests, by streams, exposed hillsides, grasslands; at elevations from 100 - 3,000 metres[].

Properties

Edibility Rating
Habit	Fern
Height	1.00 m
Cultivation Status	Ornamental, Wild

Cultivation Details

Osmunda japonica is cold-hardy to at least -20°c, they are evergreen in warm winter areas but deciduous elsewhere[].
Likes a soil of swamp mud and loamy or fibrous peat, sand and loam[]. Succeeds in most moist soils, preferring acid conditions[]. Requires a constant supply of water, doing well by ponds, streams etc[]. Plants thrive in full sun so long as there is no shortage of moisture in the soil and also in shady situations beneath shrubs etc[].
Members of this genus are rarely if ever troubled by browsing deer[].
This species is closely related to Osmunda regalis[].

Edible Uses

Young fronds - cooked[, , ].

An edible starch is obtained from the rhizome[, ].

Medicinal

None known

Other Uses

None known

Propagation

Spores - they very quickly lose their viability (within 3 days) and are best sown as soon as they are ripe on the surface of a humus-rich sterilized soil in a lightly shaded place in a greenhouse. Keep the compost moist, preferably by putting a plastic bag over the pot. Plants develop very rapidly, pot on small clumps of plantlets as soon as they are large enough to handle and keep humid until they are well established. Do not plant outside until the ferns are at least 2 years old. Cultivars usually come true to type[].
Division of the rootstock in the dormant season. This is a very strenuous exercise due to the mass of wiry roots[].