Giant Holly Fern, Western swordfern

Polystichum munitum

Physical Characteristics

Polystichum munitum is an evergreen Fern growing to 1 m (3ft 3in) by 0.3 m (1ft). See above for USDA hardiness. It is hardy to UK zone 4. It is in leaf all year. Suitable for: light (sandy) and medium (loamy) soils. Suitable pH: mildly acid, neutral and basic (mildly alkaline) soils. It can grow in full shade (deep woodland) or semi-shade (light woodland). It prefers dry or moist soil.

Distribution

Western N. America - Alaska to California.

Habitats

Woodland Garden Dappled Shade; Shady Edge; not Deep Shade; Ground Cover;

Edible Uses

Edible Parts: Root Edible Uses: Root - roasted[2, 105, 118, 161]. Peeled and then baked like potatoes[213]. The roots were generally viewed by the native North American Indians mainly as a famine food for use when little else was available[256]. The roots were generally harvested in the spring, before the plant came into growth then cooked and peeled before being eaten[256].

Medicinal Uses

Antidandruff Birthing aid Poultice An infusion of the fronds has been used as a wash or poultice to treat boils and sores[213, 257]. The young shoots have been chewed and eaten as a treatment for cancer of the womb and to treat sore throats and tonsillitis[257]. The leaves have been chewed by women to facilitate childbirth[257]. The sporangia have been crushed and applied as a poultice to burns, sores and boils[213, 257]. A decoction of the rhizomes has been used in the treatment of dandruff[213, 257].

Known Hazards

Although we have found no reports of toxicity for this species, a number of ferns contain carcinogens so some caution is advisable[200]. 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[172].