Weed Information: Spirodela polyrrhiza (duckweed, giant)
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Spirodela polyrrhiza (duckweed, giant)

Family: Lemnaceae

Description

Floating plants with a group of 4 - 12 roots attached to the lower side of the leaves which are 3 - 10 mm across with 5 - 11 prominent arcuate veins. These leaves often occur in groups and are purplish on the lower side.

Characteristics

Flower Color
  • Green
Inflorescence Type (How the flowers are arranged on the plant)
  • Axillary cluster
Number of Petals
  • 0 (no petals)
Flower Symmetry
  • Flowers regular
Flower Length (Head length in the Asteraceae)
  • < 1 mm (< .04 inch)
Flower Width (Head width in the Asteraceae)
  • < 1 mm (< .04 inch)
Number of Sepals
  • sepals lacking
Flower Sex
  • Unisexual (monoecious or dioecious)
Number of Styles
  • Styles lacking (male flowers only)
  • 1 style
Number of Stamens
  • stamens lacking (female flowers only)
  • 1 stamen
  • 2 stamens
Stamens Attached to the Petals
  • Stamens NOT attached to the petals
Stamens Connate (united)
  • Filaments or anthers NOT united

Carpel Separation
  • Carpels united (or one)
Number of Carpels
  • 0 (male flowers only or plants producing spores)
  • 1 carpel
Ovary Position
  • Superior (hypogynous)
Fruit Type
  • Utricle
Fruit Length at Maturity
  • 1 mm (.04 inch) or less
Fruit Width at Maturity
  • 1 mm (.04 inch) or less
Burs
  • Fruit or seed NOT bur-like

Leaf Arrangement
  • All basal
  • Opposite
  • Fascicled
Leaf Type
  • Simple (including lobed leaves)
Stipules
  • Lacking
Tendrils
  • Tendrils absent
Venation
  • Arcuate
Petiole (leaf stem) Blade Ratio
  • Petiole absent (leaf sessile)
Leaf Length (blade PLUS petiole)
  • 5 - 10 mm (.20 - .40 inch)
Leaf Width
  • 1 - 5 mm (.04 - .20 inch)
  • 5 - 10 mm (.20 - .40 inch)
Leaf Shape (simple leaves only)
  • Orbicular (round)
Leaf or Leaflet Margin
  • Entire
Leaf or Leaflet Blade Base
  • Rounded
Leaf or Leaflet Tip
  • Rounded (obtuse)
Leaf or Leaflet Blade Surface
  • Glabrous (NO hairs)
Succulence
  • Not succulent

Milky Juice
  • Juice NOT milky (watery)
Woodiness
  • Herbaceous
Spines or Thorns
  • Spines or Thorns ABSENT
Aromatic (vegetative structures)
  • Not aromatic
Life Cycle
  • Annual
Plant Height at Maturity
  • < 1 cm (< .40 inch)
Wind Dissemination
  • Not wind disseminated
Moisture Regime
  • Aquatic
Chlorophyll
  • Present
Growth Habit (while flowering)
  • Floating

Root or Vegetative Propagule
  • Fibrous

US State
  • Alabama
  • Arkansas
  • Connecticut
  • Delaware
  • Florida
  • Georgia
  • Illinois
  • Kansas
  • Kentucky
  • Louisiana
  • Massachusetts
  • Maine
  • Michigan
  • Missouri
  • Mississippi
  • North Carolina
  • New Hampshire
  • New Jersey
  • New York
  • Ohio
  • Pennsylvania
  • South Carolina
  • Tennessee
  • Texas
  • Virginia
  • Wisconsin
  • West Virginia
  • Hawaii
  • Indiana
  • Maryland
  • Rhode Island
  • Vermont
  • Arizona
  • California
  • Colorado
  • Iowa
  • Idaho
  • Minnesota
  • Montana
  • North Dakota
  • New Mexico
  • Nevada
  • Oklahoma
  • Oregon
  • South Dakota
  • Utah
  • Washington
  • Wyoming
  • Nebraska
Canadian Province or Territory
  • British Columbia
  • New Brunswick
  • Nova Scotia
  • Ontario
  • Prince Edward Island
  • Quebec
  • Alberta
  • Manitoba
  • Saskatchewan
Other
  • Puerto Rico
  • District of Columbia

  • Aquatic and Riparian Plants of the West, 2003 (ISBN# 1-879906-59-7) See page: 49
  • Weeds of the Northern U.S, and Canada, 1999 Royer and Dickinson, (ISBN# 1-55105-221-0) See page: 127
  • Weeds of the United States and Their Control, Lorenzi 1987, ISBN# 0-442-25884-4 See page: 89
  • Listed as a `Weed` by the Biota of North America Program, 2008 x
  • Listed in the WSSA Composite List of Weeds X
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