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Native Plant Trust: Go Botany Discover thousands of New England plants

Ambrosia trifida — giant ragweed

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Facts

Giant ragweed inhabits many of the same disturbed sites as common ragweed, but the two can be easily distinguished, as giant ragweed is very much larger and its leaves are far less dissected. It shares with common ragweed the allergenicity of its wind-dispersed pollen. It was used medicinally by Native American tribes including the Cherokee, Iroquois, Lakota and Meskwaki, and in former times the seeds may have been a food source, as seed caches have been found in ancient settlements.

Habitat

Anthropogenic (man-made or disturbed habitats)

New England distribution

Adapted from BONAP data

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North America distribution

Adapted from BONAP data

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Characteristics

Habitat
terrestrial
New England state
  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Rhode Island
  • Vermont
Leaf type
leaves are simple (i.e., lobed or unlobed but not separated into leaflets)
Leaf arrangement
opposite: there are two leaves per node along the stem
Leaf blade edges
  • the edge of the leaf blade has lobes, or it has both teeth and lobes
  • the edge of the leaf blade has no teeth or lobes
  • the edge of the leaf blade has teeth
Flower type in flower heads
the flower head has disk flowers only, and lacks the strap-shaped flowers
Ray flower color
NA
Tuft or plume on fruit
NA
Spines on plant
the plant has no spines
Leaf blade length
40–250 mm
Flower head width
2–4 mm
Disk flower number
  • 1-5
  • 11-20
  • 21-50
  • 6-10
Show all characteristics

  • Flowers

    Bases of bract appendages
    NA
    Bract color
    the bracts are not colored or tinged with pink, red or purple
    Bract cycle number
    there is one main cycle of bracts
    Bract outer side hair type
    the bracts are hairy, with simple hairs on their outer surface
    Bract outer side hairs
    the bracts are hairy on their outer surfaces
    Bract separation
    at least some flower heads have bracts connected to one another at or near their bases
    Bract texture
    the bracts appear leathery or hardened
    Bract tip extension edge
    there are no projections from the bract tips
    Bracts
    there are at least two distinct forms of bracts in different cycles
    Disk flower color
    green to brown
    Disk flower lobe number
    5
    Disk flower number
    • 1-5
    • 11-20
    • 21-50
    • 6-10
    Disk flower reproductive parts
    the disk flower has either only pollen- or only seed-producing parts
    Disk flower shape
    the disk flower is tube-shaped (cylindrical), or gradually widening like a funnel
    Flower head number
    • each flowering stem has four or more flower heads on it
    • each flowering stem has only one to three flower heads on it
    Flower head outer flowers
    at the outer edge of the flower head, the flowers have no enlarged lobe or strap, and are of similar size as those in the center of the disk
    Flower head platform
    the base has no bristles or papery scales
    Flower head position
    some or all the flower heads are grouped in clusters of two or more
    Flower head profile
    the disk is flat or nearly flat across the top
    Flower head shape
    the flower head is cup-shaped (the sides diverge, then curve upwards and become parallel)
    Flower head width
    2–4 mm
    Flower type in flower heads
    the flower head has disk flowers only, and lacks the strap-shaped flowers
    Height of flower head base
    7–12 mm
    Inflorescence branching (Solidago)
    NA
    Inflorescence shape
    • the flower heads grow in clusters from the axils of the branches or leaves
    • the inflorescence is not flat-topped but appears rounded, with some flower heads distinctly higher than others
    Inflorescence stem
    hairs are present on the stem of the inflorescence
    Ovary beak
    there is a beak on the ovary
    Ovary cross-section
    the ovary is roughly square or with four corners
    Ovary hair type
    the ovary has no hairs on it
    Ovary hairs
    the ovary has no hairs on it
    Ovary profile
    • in profile, the ovary is roughly egg-shaped, but widest above the middle
    • in profile, the ovary is roughly elliptical (widest in the middle, tapering to both ends)
    Peduncle length
    2–7 mm
    Ray flower color
    NA
    Ray flower reproductive parts
    NA
    Ray flowers
    0
    Ray length
    0 mm
    Reproductive system
    the flowers on the plant may have either carpels or stamens, but always in separate flowers
    Smaller bracts at base of bracts
    there is no smaller, outer cycle of bracts
    Style branch number
    the style has one branch
    Width of flower head base
    5–10 mm

  • Fruits or seeds

    Number of pappus parts
    0
    Ovary length in developed fruit
    5–10 mm
    Seed hair tuft bases
    NA
    Seed hair tuft color
    NA
    Seed hair tuft details
    NA
    Seed hair tuft length
    0 mm
    Seed hair tuft tips
    NA
    Seed hairs uniform
    NA
    Seed tuft scale number
    0
    Seed tuft type
    there is no pappus on the ovary
    Top of disk flower ovary
    NA
    Tuft or plume on fruit
    NA

  • Glands or sap

    Leaf blade glands
    the leaf blades have glandular (translucent) dots or scales
    Sap
    the sap is clear and watery

  • Growth form

    Growth form
    the plant has one or more free-standing stems
    Plant lifespan
    the plant is annual, it lacks evidence of previous years' growth
    Spines on plant
    the plant has no spines
    Underground organs
    there is a thickened taproot on the plant

  • Leaves

    Final leaf segment width (compound lvs only)
    20–70 mm
    Hairs on underside of leaf blade
    the underside of the leaf is fuzzy or hairy
    Hairs on upper side of leaf blade
    the upper side of the leaf is fuzzy or hairy
    Leaf arrangement
    opposite: there are two leaves per node along the stem
    Leaf blade base
    the leaf has a distinct petiole
    Leaf blade base shape
    • the base of the leaf blade is cuneate (wedge-shaped, tapers to the base with relatively straight, converging edges), or narrow
    • the base of the leaf blade is truncate (ends abruptly in a more or less straight line as though cut off)
    Leaf blade bloom
    the underside of the leaf has no noticeable bloom
    Leaf blade edges
    • the edge of the leaf blade has lobes, or it has both teeth and lobes
    • the edge of the leaf blade has no teeth or lobes
    • the edge of the leaf blade has teeth
    Leaf blade hairs
    • the leaf blade has hairs with glands at their tips
    • the leaf blade has simple hairs with no glands, and not tangled or wooly
    Leaf blade length
    40–250 mm
    Leaf blade shape
    • the leaf blade is elliptic (widest near the middle and tapering at both ends)
    • the leaf blade is lanceolate (lance-shaped; widest below the middle and tapering at both ends)
    • the leaf blade is ovate (widest below the middle and broadly tapering at both ends)
    • the leaf blade is triangular, with the stalk or attachment point on one of the sides
    Leaf blade surface colors
    there is no noticeable color variation on the upper surface of the leaf
    Leaf blade tip
    the tip of the leaf blade is acuminate (tapers to a long, thin point)
    Leaf blade veins
    the leaf blade has one main vein running from the base towards the tip
    Leaf blade width
    30–200 mm
    Leaf disposition
    the leaves are nearly similar in size, prominence of teeth, and length of stalks throughout the stem
    Leaf spines
    there are no spines on the leaf edges
    Leaf stalk
    the leaves have leaf stalks
    Leaf stalk length
    10–70 mm
    Leaf tip extension
    NA
    Leaf type
    leaves are simple (i.e., lobed or unlobed but not separated into leaflets)
    Leaflet number
    0
    Specific leaf type
    • the leaf has a row of two or more lobes on each side of the central axis
    • the leaf has a row of two or more lobes on each side of the central axis, and each lobe itself has rows of lobes on each side of the lobe's central axis
    • the leaf has lobes that radiate from the base, somewhat like a hand
    • the leaves are simple (i.e., lobed or unlobed but not separated into leaflets
    Teeth per side of leaf blade
    At least 0

  • Place

    Habitat
    terrestrial
    New England state
    • Connecticut
    • Maine
    • Massachusetts
    • New Hampshire
    • Rhode Island
    • Vermont
    Specific habitat
    man-made or disturbed habitats

  • Scent

    Plant odor
    the plant does not have much of an odor

  • Stem, shoot, branch

    Flowering stem cross-section
    the flowering stem is circular, or with lots of small angles
    Leaves on stem
    there is at least one full leaf above the base of the flowering stem
    Stem bloom
    there is no powdery or waxy film on the stem
    Stem internode hair direction
    the hairs point mostly upwards to outwards
    Stem internode hair length
    At least 0 mm
    Stem internode hair type
    • the hairs on the stem are plain, without glands or branches, and not tangled
    • the stem has no hairs between the nodes
    Stem internode hairs
    • the stem has hairs between the nodes
    • the stem has no hairs between the nodes
    Stem wings
    the stem does not have wings on it

Wetland status

Occurs in wetlands or non-wetlands. (Wetland indicator code: FAC)

In New England

Distribution

Connecticut
present
Maine
present
Massachusetts
present
New Hampshire
present
Rhode Island
present
Vermont
present

Conservation status

Exact status definitions can vary from state to state. For details, please check with your state.

var. trifida

Massachusetts
widespread (S-rank: S5)
New Hampshire
unrankable (S-rank: SU), Ind (code: Ind)

Subspecies and varieties

Our variety is Ambrosia trifida L. var. trifida.

From Flora Novae Angliae dichotomous key

4.  Ambrosia trifida L. var. trifida N

giant ragweed. Ambrosia trifida L. var. integrifolia (Muhl. ex Willd.) Torr. & Gray • CT, MA, ME, NH, RI, VT. Edges of cultivated fields, barnyards, railroads, disturbed soil.

1×4. Ambrosia artemisiifolia × Ambrosia trifida → Ambrosia ×‌helenae Rouleau is an extremely rare ragweed hybrid known only from CT in New England. It ismost likely to be confused with A. trifida due to the palmately or subpalmately lobed leaf blades. However, the upper leaves (i.e., those subtending branches of the capitulescence) are frequently alternate, the lobes on the blades are often with additional lobes, and the staminate involucres have relatively weak veins (vs. leaves opposite throughout, lobes on leaf blades without additional lobes, and staminate involucres with 3 (–4) strong veins on one side in A. trifida).

Native to North America?

Yes and no (some introduced)

Synonyms

  • Ambrosia trifida var. integrifolia (Muhl. ex Willd.) Torr. & Gray

Family

Asteraceae

Genus

Ambrosia