Illinois Natural History Survey - University of Illinois

Ambrosia trifida
Horseweed, Giant ragweed, Great ragweed
Taxonomy

Synonyms: Ambrosia trifida texana, Ambrosia trifida var. texana

Subspecific taxa:

Classification:

Other taxonomic & nomenclature sources: USDA Plants;  ITIS;  The Plant List;  IPNI

Images

   
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Species Distribution
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More about map & occurrence records

County Map Legend
Absent:
Not known from county
Medium confidence:
Medium or unknown confidence;
often old records or unverifiable observations
Medium-high confidence:
Often observations by expert botanists
High confidence:
Often vouchered herbarium records
Planted / introduced:
Native species introduced outside historic range,
or only in planted locations within county (e.g., restorations)
Historic / extirpated:
Only historic records for the species; likely extirpated
(Note that this category is not yet functional)

North American distribution maps for this species: FLNA;  USDA Plants;  BONAP;  BISON

Collections, Observations & Flowering by Month [?]

J
0
F
0
M
0
A
0
M
0
J
0
J
0
A
0
S
0
O
0
N
0
D
0

Collections & Observations by Decade [?]

Species Status

Status/Listing: No Information

Notes:

Origin:

Species Description

General: Dicot-herb, annual

Roots:

Shoots: opposite leaf arrangment; simple leaf type; Pinnate leaf venation; lanceolate leaf shape

Inflorescence:

Flowers: unisexual, monoecious; 5 merous; incomplete, not sepals; yellow, green; epigynous ovary position

Fruit: achene

Physiology: autotrophic; C3 C02 fixation

Reproduction: sexual

Ecology & Natural History

Habitat: Waste places, rich alluvial soils in thickets, sloughs, roadsides, and along railroads. Likes moister sites than A. artemesiifolia. Rich alluvial soils in sloughs, waste grounds, roadsides, along railroads.

ILPIN Notes: Often forms extensive acres of thousands of plants. This plant is probably one of the commonest causes of hayfever. As a hayfever source, it far outnumbers A. artemestiifolia; plant was used as an astringent in chronic catarrhal infections. Early bluff-dwellers of Ozarks used cultivated strains with large achenes for food. Herbicides and brush poisons, pulling. Sterile heads, short pedunculate, leaves palmately 3 to 5 lobed or undivided. Typical variety has petioles of at least upper leaves wing-margined, larger fruits, and ribs of fruit ending in short spines. SCS V.2 = Ambrosia aptera DC. - these two names have been used for the same plant by at least one source. The typical variety has: wingless petioles; fruits, mostly smaller and ribs of fruit ending in blunt or almost obsolete tubercles. Adventive from S.W. USA.

Functional Relationships:

  • Pollinators: wind
  • Dispersal:
  • Mycorrhizae:
  • N2 fixation:

Human Relationships:

  • Edibility [?] :
  • Showy Flowers:

Wildlife and Livestock Information:

  • Food Value:
  • Cover Value:

Coefficient of Conservatism (C-value) [?] :

  • Entire State: 0
  • Chicago Area: 0

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