pseudacorus – pseudo meaing ‘false’ + Acorus (sweet flag common in wetlands of Asia) because the rhizomes and flattened leaves resemble one another

Native range: Europe, W. Asia, NW Africa

Leaves:

• basal leaves
• stiff
• narrowly linear
• 5–9 dm. long
• 10–15 mm. broad
• cauline leaves reduced upward
• mostly basal, folded and clasp the stem at the base in a fan-like fashion
• leaves sometimes die back over winter, but persist if winters are mild

Flowers:

• showy yellow flowers
• several flowers can occur on each stem, along with one or two leafy bracts
• inflorescence:
  • branched
  • few to several flowered
  • 1.5-5 dm. long
• pale to deep yellow
• purple-lined
• pedicles up to 5 cm. long
• perianth parts fused in a tube at the base, the tube about about 12 mm. long
• 3 obovate, spreading, ~5 cm long sepals
• 3 upright petals, much shorter and narrower than the sepals
• 3 stamens, opposite the sepals
• 3 branched style, about 22 mm. long with 2 terminal lobes less than as long
• triangular stigma
• inferior ovary

Fruit:

• capsule
• triangular
• 3-celled
• leathery
• 5–8 cm. long
• seeds are corky

Other characteristics:

• monocot
• herbaceous perennial from short, thick rhizomes
• forms dense expanding clumps (3–4’ (~ to 5’) tall and to 30” wide)
• simple, leafy flowering stem up to 1 m. tall

Ecology & Adaptations:

• native to Europe to western Siberia, Caucasus, northern Africa
• garden “escape” widely distributed throughout much of Washington
• widely distributed throughout much of North America in temperate climates
• found in ditches and ponds at low elevations; forms large colonies along streams, ponds and marshes
• rows in water to 25 cm deep, or very near water, such as lakeside muds
• pollinated by bumble-bees and long-tongued flies
• seed dispersal – seeds that mature and drop into water can float to other locations, aided by a corky constitution
• vegetative reproduction:
  • via underground rhizomes, forms very dense monotypic stands, outcompeting other plants
  • able to re-sprout if top damaged or killed
• tolerant of anoxia – oxygen transported through spongy tissue (aerenchyma) to rhizomes below water
• tolerant of drought – underground rhizomes remain viable
• herbivore defense:
  • tissues contain compounds that deter feeding (although muskrats will eat the rhizomes)
  • contact with the resins can cause skin irritation in animals
• control:
  • dig up small isolated patches with pick-axes or hatchets, making sure to get the entire rhizome
  • repeated mowing or cutting may keep yellow flag iris contained and can potentially kill it by depleting the energy in the rhizomes after several years of intensive mowing
  • herbicides for use in aquatic systems may be the most effective and cost-effective option for eradication of large infestations