Iris tenax

From Puget Prairie Plants

Common name: Oregon Iris or Tough Leaved Iris

Iris tenax flower in bloom

Abbreviation code (Codon): IRTE


  • Kingdom: Plantae
  • (unranked): Angiosperms
  • (unranked): Monocots
  • Order: Asparagales
  • Family: Iridaceae
  • Subfamily: Iridoideae
  • Genus: Iris
  • Subgenus: Limniris
  • Species: I. tenax


A tufted perennial with narrow, grass-like leaves and showy flowers on thin, wand-like stems to 14 in. tall. Leaves slightly exceed the flower stem in height. The flower of this species shows considerable variation in color, from white to deep purple. Large, delicate, lavender to deep purple (sometimes white, rarely yellow) flowers, commonly with dark violet veins, grow at top of short stalks in dense clumps. Flowers usually occur singly but sometimes in pairs.

  • Leaves: Leaves mostly basal, narrowly linear, up to 4 dm. long and 2-6 mm. broad; cauline leave few, reduced upward.
  • Flowers: Lavender or blue to purple, but occasionally white to yellow or pinkish, subtended by a pair of involucral leaves which may be 2 cm. apart; pedicels 1-4 cm. long; perianth parts fused in a tube at the base, the tube 6-10 mm. long; sepals 3, oblanceolate to obovate, 5.5-6.5 cm. long, spreading; petals 3, oblanceolate, 3.5-6 cm. long, erect; style branches 25-30 mm. long with 2 terminal lobes 8-12 mm. long; stigmas triangular; ovary inferior.
  • Fruit: Capsule 3-celled, leathery, 25-35 mm. long

Bloom Period

June - August


West of the Cascades, Thurston and Grays Harbor Counties, Washington, south to southwest Oregon


Prairies and pastures, open oak and coniferous forests, low elevations


  • A tincture of the whole plant, or the bulbous stems, is given in the treatment of bilious vomiting and is recommended for treating depression. A fiber from the leaves is used in weaving and making ropes. The fiber is buoyant, strong and durable. Tenax, Latin for tenacious, refers to the tough leaves.
  • Warning: Some Iris species are known to be poisonous to humans and animals if eaten (especially the rhizome, or root), and it is likely that all irises contain toxins. Plant juices can cause blisters on the skin. POISONOUS PARTS: Rhizomes (thickened roots) and rootstocks, fresh or dry. Minor skin irritation when touched, low toxicity if ingested. Symptoms include nausea, vomiting, abdominal pain, diarrhea, elevated temperature following ingestion; skin irritation upon contact with seeds, rootstock, or cell sap. Toxic Principle: Irisin, iridin, or irisine.


Iris tenax does not spread quickly, but will form large clumps of underground bulbous stems. It requires wet soil in the spring time and well drained soil during the drier months.

Iris tenax seeds
photo by Lisa Hintz


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