Weed Information: Ambrosia trifida (ragweed, giant)
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Ambrosia trifida (ragweed, giant)

Family: Asteraceae

Description

Plants variable, but often up to 10 feet tall. The leaves have 3 fairly even lobes. This is the classic hay-fever plant, releasing massive amounts of windblown pollen from the small, pendulous heads of male flowers.

Characteristics

Flower Color
  • Green
Inflorescence Type (How the flowers are arranged on the plant)
  • Axillary racemes
  • Head
  • Terminal raceme
Number of Petals
  • 0 (no petals)
  • 5 petals
Petal Separation
  • United > 75% of length
Petal Tip
  • Pointed
Flower Symmetry
  • Flowers regular
Flower Length (Head length in the Asteraceae)
  • 3 mm (.12 inch)
  • 4 mm (.16 inch)
  • 5 mm (.20 inch)
  • 6 mm (.24 inch)
  • 7 mm (.28 inch)
  • 8 mm (.32 inch)
  • 9 mm (.36 inch)
  • 1.0 cm (.40 inch)
Flower Width (Head width in the Asteraceae)
  • 2 mm (.08 inch)
  • 3 mm (.12 inch)
  • 4 mm (.16 inch)
  • 5 mm (.20 inch)
Number of Sepals
  • sepals lacking
  • 5 sepals
  • 6 sepals
  • 7 sepals
  • 8 sepals
  • 9 sepals
  • 10 sepals
  • more than 10 sepals
Sepal Separation
  • Completely free to base
Sepal Tip
  • Rounded
  • Square
Flower Sex
  • Unisexual (monoecious or dioecious)
Number of Styles
  • Styles lacking (male flowers only)
  • 1 style
Number of Stamens
  • stamens lacking (female flowers only)
  • 5 stamens
Stamens Attached to the Petals
  • Stamens attached to the petals
Stamens Connate (united)
  • Anthers united, syngynoecious

Carpel Separation
  • Carpels united (or one)
Number of Carpels
  • 0 (male flowers only or plants producing spores)
  • 1 carpel
Ovary Position
  • Inferior (epigynous)
Fruit Type
  • Achene
Fruit Length at Maturity
  • 4 mm (.16 inch)
  • 5 mm (.20 inch)
  • 6 mm (.24 inch)
Fruit Width at Maturity
  • 2 mm (.08 inch)
  • 3 mm (.12 inch)
  • 4 mm (.16 inch)
Burs
  • Fruit or seed NOT bur-like

Leaf Arrangement
  • Opposite
Leaf Type
  • Simple (including lobed leaves)
Stipules
  • Lacking
Tendrils
  • Tendrils absent
Venation
  • Palmate
Petiole (leaf stem) Blade Ratio
  • Petiole < 25% total length
  • Petiole 25% - 75% total length
Leaf Length (blade PLUS petiole)
  • 4 - 10 cm (1.60 - 4.0 inches)
  • 1 - 2 dm (4.0 - 8.0 inches)
  • 2 - 4 dm (8.0 - 16.0 inches)
Leaf Width
  • 2 - 4 cm (.80 - 1.6 inches)
  • 4 - 10 cm (1.6 - 4.0 inches)
  • 1 - 2 dm (4.0 - 8.0 inches)
Leaf Shape (simple leaves only)
  • Elliptic
  • Orbicular (round)
  • Ovate
  • Palmately 3 lobed
  • Palmately 4 - 5 lobed
Leaf or Leaflet Margin
  • Lobed
  • Parted
  • Serrate
Leaf or Leaflet Blade Base
  • Acute (cuneate)
  • Acuminate (attenuate)
Leaf or Leaflet Tip
  • Acuminate (attenuate)
  • Acute
Leaf or Leaflet Blade Surface
  • Scabrous (like sand paper)
Succulence
  • Not succulent

Milky Juice
  • Juice NOT milky (watery)
Woodiness
  • Herbaceous
Spines or Thorns
  • Spines or Thorns ABSENT
Aromatic (vegetative structures)
  • Not aromatic
  • Aromatic
Life Cycle
  • Annual
Growth Habit (while flowering)
  • Erect, columnar (narrow)
Plant Height at Maturity
  • 1 - 1.5 meters (3.3 - 5.0 feet)
  • 1.5 - 2.0 meters (5.0 - 6.6 feet)
  • 2 - 2.5 meters (6.6 - 8.3 feet)
  • 2.5 - 5 meters (8.3 - 16.6 feet)
Wind Dissemination
  • Not wind disseminated
Moisture Regime
  • Seasonally saturated
  • Mesic
Chlorophyll
  • Present

Stem Cross Section
  • Round
Flowering Stem Leaves
  • Stem uniformly leafy
Main Stem Branches
  • Main stem branched

Root or Vegetative Propagule
  • Tap Root

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
  • Indiana
  • Maryland
  • Rhode Island
  • Vermont
  • Arizona
  • California
  • Colorado
  • Iowa
  • Idaho
  • Minnesota
  • Montana
  • North Dakota
  • New Mexico
  • 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
  • District of Columbia

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  • 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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