Practical
Plants

Osmunda japonica

Zenmai

a member of the Osmunda genus in the family Osmundaceae.

No photo available

Taxonomy and growth

Genus
Osmunda
Height
1 m

Uses

Toxicity

Toxicity warning. The historical record reports a hazard for this plant. Do not use it to decide which parts are safe to eat or use medicinally.

This section contains historical Plants For A Future notes marked noncommercial.

Although we have found no reports of toxicity for this species, a number of ferns contain carcinogens so some caution is advisable[5]. 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[3].

Edible uses

This section contains historical Plants For A Future notes marked noncommercial.

Young fronds - cooked[2][4]. An edible starch is obtained from the rhizome[2][4].

Plant part
Leaves
Plant part
Root

Environment

Range
E. Asia - China, Japan.
Habitat
Moist places all over Japan[7][5].
Light
full sun
Shade tolerance
light shade
Water
high
Hardiness
Zone 6+
Soil textures
sandy, loamy, clay
Soil pH
very acid, acid, neutral, alkaline
Tolerates Nutritionally Poor Soil
No
Drought
intolerant

Propagation

This section contains historical Plants For A Future notes marked noncommercial.

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[5]. Division of the rootstock in the dormant season. This is a very strenuous exercise due to the mass of wiry roots[5].

Cultivation

This section contains historical Plants For A Future notes marked noncommercial.

Likes a soil of swamp mud and loamy or fibrous peat, sand and loam[1]. Succeeds in most moist soils, preferring acid conditions[5]. Requires a constant supply of water, doing well by ponds, streams etc[1]. 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[5]. Plants are hardy to at least -20°c, they are evergreen in warm winter areas but deciduous elsewhere[5]. Members of this genus are rarely if ever troubled by browsing deer[6]. Closely related to O. regalis[1].

References

  1. F. Chittendon. RHS Dictionary of Plants plus Supplement. 1956 Oxford University Press 1951-00-00

    ↩1↩2↩3

  2. Tanaka. T. Tanaka's Cyclopaedia of Edible Plants of the World. Keigaku Publishing 1976-00-00

    ↩1↩2

  3. Schofield. J. J. Discovering Wild Plants - Alaska, W. Canada and the Northwest.

    ↩

  4. Kunkel. G. Plants for Human Consumption. Koeltz Scientific Books 1984-00-00 ISBN 3874292169

    ↩1↩2

  5. Huxley. A. The New RHS Dictionary of Gardening. 1992. MacMillan Press 1992-00-00 ISBN 0-333-47494-5

    ↩1↩2↩3↩4↩5↩6↩7

  6. Thomas. G. S. Perennial Garden Plants J. M. Dent & Sons, London. 1990-00-00 ISBN 0 460 86048 8

    ↩

  7. Ohwi. G. Flora of Japan. (English translation) Smithsonian Institution 1965-00-00

    ↩

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