Erigeron canadensis var. canadensis

Distribution Map: Based on vouchered plant specimens only. View county names by placing the mouse cursor over a particular county.

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Family:	Asteraceae
Species:	Erigeron canadensis L.
Infraspecies:	Erigeron canadensis L. var. canadensis
Common Name:	common horseweed
Habitat:	Clearings in forests, open banks of streams, successional fields (where the soils are exposed or thin), cultivated ground, roadsides, disturbed areas, and waste areas.
Associated Ecological Communities:	**
Growth Habit:	Herbaceous
Duration:	Annual
Category:	Vascular
Plant Notes:	**
Taxonomic Notes:	**
Status:	Native, FACU (NCNE), FACU (EMP), S5 (State Rank), CoC: 0
References:	**

** Not applicable or data not available.

Classification

Supraordinal	Eudicots
Order	Asterales
Family	Asteraceae
Genus	Erigeron
Species	Erigeron canadensis
Infraspecies	Erigeron canadensis L. var. canadensis - common horseweed

Citation

Citation	Erigeron canadensis L. var. canadensis
Basionym:	**
Type:	**

** Not applicable or data not available.

Source

County	Year	Herbaria	Notes	Submission Info
Albany		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Bronx		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Cattaraugus		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Cattaraugus	1991	BUF – Herbarium # 77908 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Cattaraugus	1960	BUF – Herbarium # 58147 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Cattaraugus	1943	BUF – Herbarium # 74834 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Cattaraugus	1943	BUF – Herbarium # 74838 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Chemung		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Delaware		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Dutchess		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Erie		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Erie	1990	BUF – Herbarium # 73699 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Erie	1988	BUF – Herbarium # 67674 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Erie	1988	BUF – Herbarium # 68476 Herbarium Name Used: Conyza canadensis var. canadensis		12/18/2009 - BUF (Ed Fuchs)
Erie	1987	BUF – Herbarium # 74835 Herbarium Name Used: Conyza canadensis var. canadensis		12/18/2009 - BUF (Ed Fuchs)
Erie	1999	BUF – Herbarium # 77099 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Erie	1942	BUF – Herbarium # 74837 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Erie	1930	BUF – Herbarium # 53410 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Erie	1924	BUF – Herbarium # 74832 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Essex		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Fulton	2007	NYS – 363 Herbarium Name Used: Conyza canadensis var. canadensis		12/22/2009 - Donna Vogler
Fulton	2007	FMCC – 363 Herbarium Name Used: Conyza canadensis var. canadensis		12/22/2009 - Donna Vogler
Greene		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Hamilton		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Jefferson		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Lewis		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Livingston		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Montgomery	2005	NYS Herbarium Name Used: Conyza canadensis	Town of Amsterdam	8/30/2009 - Connie Tedesco
Montgomery	2005	FMCC Herbarium Name Used: Conyza canadensis	Town of Amsterdam	8/30/2009 - Connie Tedesco
Niagara	1976	BUF – Herbarium # 53378 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Niagara	1895	BUF – Herbarium # 67675 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Niagara	1895	BUF – Herbarium # 67676 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Niagara	1884	BUF – Herbarium # 67677 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Niagara	1986	BUF – Herbarium # 55652 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Niagara	1986	BUF – Herbarium # 55653 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Niagara	1987	BUF – Herbarium # 55838 Herbarium Name Used: Conyza canadensis var. canadensis		12/18/2009 - BUF (Ed Fuchs)
Niagara	1987	BUF – Herbarium # 58353 Herbarium Name Used: Conyza canadensis var. canadensis		12/18/2009 - BUF (Ed Fuchs)
Oneida		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Onondaga		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Ontario		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Orleans	1986	BUF – Herbarium # 74833 Herbarium Name Used: Conyza canadensis	Identification needs confirmation as the submitted data is different than where this record is place in the Atlas	12/18/2009 - BUF (Ed Fuchs)
Oswego		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Oswego	2007	RCFS – accession # 13164 Herbarium Name Used: Conyza canadensis var. canadensis		11/17/2009 - RCFS (Andy Nelson)
Otsego	2005	SUCO Herbarium Name Used: Conyza canadensis	Town of Exeter
Rensselaer		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Saratoga		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Schenectady	1950	NYS Herbarium Name Used: Erigeron canadensis var. canadensis	collector: T. Baim	3/28/2025 - Steve Young
Schoharie		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
St. Lawrence		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Suffolk	1992	CONN Herbarium Name Used: Conyza canadensis
Suffolk	1975	CONN Herbarium Name Used: none Conyza canadensis var. canadensis
Suffolk		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Suffolk	1964	BKL – BKL00080801 Herbarium Name Used: Conyza canadensis var. canadensis		2/8/2012 - BKL (Steve Glenn)
Suffolk	1962	BKL – BKL00080309 Herbarium Name Used: Conyza canadensis var. canadensis		2/8/2012 - BKL (Steve Glenn)
Ulster		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Washington		NYFA_1990 Herbarium Name Used: none Conyza canadensis var. canadensis
Westchester	1935	BH Herbarium Name Used: Erigeron canadensis var. canadensis	Werier (2017) voucher!; G. Voetsch & R.T. Clausen 2009	3/6/2018 - David Werier

Synonyms

Synonym	Full Citation	Basionym	Type	Notes
Conyza canadensis	Conyza canadensis (L.) Cronquist
Conyza canadensis var. glabrata	Conyza canadensis (L.) Cronquist var. glabrata (A. Gray) Cronquist
Leptilon canadense	Leptilon canadense (L.) Britton

Listed Status: New York

Listed Status:	(New York): Rare plants are protected under New York State Environmental Conservation Law section 9-1503. Part (f) which reads as follows: "It is a violation for any person, anywhere in the state to pick, pluck, sever, remove, damage by the application of herbicides or defoliants, or carry away, without the consent of the owner, any protected plant. Each protected plant so picked, plucked, severed, removed, damaged or carried away shall constitute a separate violation." At this time, the Atlas only identifies those species listed as threatened or endangered.
Endangered: 5 or fewer extant sites, or fewer than 1,000 individuals, or restricted to fewer than 4 U.S.G.S. 7 1/2 minute topographical maps, or species listed as endangered by the U. S. Department of Interior, as enumerated in the Code of Federal Regulations 50 CFR 17.11.
Threatened: 6 to fewer than 20 extant sites, or 1,000 to fewer than 3,000 individuals, or restricted to not less than 4 or more than 7 U.S.G.S. 7 1/2 minute topographical maps, or listed as threatened by the U. S. Department of the Interior, as enumerated in the Code of Federal Regulations 50 CFR 17.11.
Rare: 20 to 35 extant sites, or 3,000 to 5,000 individuals statewide.
Exploitably vulnerable:	species which are likely to become threatened in the near future throughout all or a significant portion of their range within the state if causal factors continue unchecked.

Listed Status: US

Listed Status: US	(U.S.) Source - List of Endangered and Threatened Wildlife and Plants under the provisions of the Endangered Species Act of 1973, as amended.
Endangered:	Any species which is in danger of extinction throughout all or a significant portion of its range.
Threatened:	Any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range.

WAP: Wetland AssessmentProcedure

Wetland Assessment Procedure (WAP): Source - Southwest Florida Water Management District, Wetland Assessment Procedure Instruction Manual for Isolated Wetlands (March 2005).

AD:	Adaptive Species. Plant species designated as FAC or Upland by DEP, but commonly seen in the transition zone in limited numbers.
D:	Deep Species. Plant species commonly found in the deep zone, and designated either FAC or OBL by DEP.
OD:	Outer Deep Species. Plant species commonly found in the outer deep zone, and designated either FACW or OBL by DEP.
T:	Transition Species. Plant species commonly found in the transition zone, and designated either FACW or OBL by DEP.
U:	Upland Species. Plant species that are not expected to be seen in wetlands.

ANY - WAP critieria is not taken into consideration
Yes - Show results with WAP designations
No - Show results without WAP designations

EPPC: Exotic Pest Plant Council

EPPC:

Source - Florida Exotic Pest Plant Council's 2007 List of Florida's Most Invasive Species

Category I - Species that are invading and disrupting native plant communities in Florida. This definition does not rely on the economic severity or geographic range of the problem, but on the documented ecological damage caused.

Category II - Species that have shown a potential to disrupt native plant communities. These species may become ranked as Category I, but have not yet demonstrated disruption of natural Florida communities.

DEP: Department of Environmental Protection

Wetland Status, Department of Environmental Regulation (DEP): Source - Delineation of the Landward Extent of Wetlands and Surface Waters, Chapter 62-340, Florida Administrative Code. 1994.

OBL:	Obligate wetland. Occurs almost always under natural conditions in wetlands.
FACW:	Facultative Wetland. Usually occurs in wetlands, but occasionally found in non-wetlands
FAC:	Facultative. equally likely to occur in wetlands or non-wetlands.

NWPL: National Wetland Plant List

National Wetland Plant List (NWPL): Source - Lichvar, R.W., M. Butterwick, N.C. Melvin, and W.N. Kirchner. 2014. The National Wetland Plant List: 2014 Update of Wetland Ratings. Phytoneuron 2014-41: 1-42.

OBL:	Obligate Wetland. Occurs almost always (estimated probability 99%) under natural conditions in wetlands.
FACW:	Facultative Wetland. Usually occurs in wetlands (estimated probability 67%-99%), but occasionally found in non-wetlands.
FAC:	Facultative. Equally likely to occur in wetlands or non-wetlands (estimated probability 34%-66%).
FACU:	Facultative Upland. Usually occurs in non-wetlands (estimated probability 67%-99%), but occasionally found in wetlands (estimated probability 1%-33%).
UPL:	Obligate Upland. Occurs in wetlands in another region, but occurs almost always (estimated probability 99%) under natural conditions in non-wetlands in the regions specified.

NWPL: National Wetland Plant List (NCNE and EMP Regions)

National Wetland Plant List (NWPL): Source - U.S. Army Corps of Engineers 2020. National Wetland Plant List, version 3.5 https://wetland-plants.sec.usace.army.mil/nwpl_static/v34/home/home.html U.S. Army Corps of Engineers, Engineer Research and Development Center, Cold Regions Research and Engineering Laboratory, Hanover, NH.

Indicator status rating definitions according to Lichvar et al. 2012.

OBL:	Obligate Wetland Plants - almost always occur in wetlands.
FACW:	Facultative Wetland Plants - usually occur in wetlands, but may occur in non-wetlands.
FAC:	Facultative Plants - occur in wetlands and non-wetlands.
FACU:	Facultative Upland Plants - usually occur in non-wetlands, but may occur in wetlands.
UPL:	Upland Plants - almost always occur in uplands.

Wetland indicator status ratings are provided for each of the two regions that exist in NY, the Northcentral and Northeast Region (NCNE) and the Eastern Mountains and Piedmont Region (EMP). See the Atlas guide for further details.

NWPL: National Wetland Plant List (NCNE and EMP Regions)

Indicator status rating definitions according to Lichvar et al. 2012.

OBL:	Obligate Wetland Plants - almost always occur in wetlands.
FACW:	Facultative Wetland Plants - usually occur in wetlands, but may occur in non-wetlands.
FAC:	Facultative Plants - occur in wetlands and non-wetlands.
FACU:	Facultative Upland Plants - usually occur in non-wetlands, but may occur in wetlands.
UPL:	Upland Plants - almost always occur in uplands.

Persisting

Identifying species that appear as waifs or only periodically appear in the flora for a few seasons.

Any - Persisting critieria is not taken into consideration
Yes - Show results with a Persisting value of Y
No - Show results without Persisting value of N

Duration

Annual:	Plants that perform their entire lifecycle within a single growing season. All roots, stems, and leaves die at the end of the growing season. Over wintering seeds allow the next generation to appear.
Biennial:	A plant that is typically vegetative its first year and blooms the following season. Once it has bloomed and set seed, the plant dies. Garlic mustard is an example of a biennial.
Perennial:	These plants live for three or more seasons. Many perennials may not be mature enough to bloom during its first year. Perennial wildflowers re-grow each season from overwinter root material.

Category

Vascular:	Any of various plants that have the vascular tissues xylem and phloem. The vascular plants include all seed-bearing plants (the gymnosperms and angiosperms) and the pteridophytes (including the ferns, lycophytes, and horsetails). Also called tracheophyte.
Bryophyte:	A large group of seedless green plants including the mosses, liverworts, and hornworts. Bryophytes lack the specialized tissues xylem and phloem that circulate water and dissolved nutrients in the vascular plants. Bryophytes generally live on land but are mostly found in moist environments, for they have free-swimming sperm that require water for transport. In contrast to the vascular plants, the gametophyte (haploid) generation of bryophytes constitutes the larger plant form, while the small sporophyte (diploid) generation grows on or within the gametophyte and depends upon it for nutrition.
Lichen:	The mutualistic symbiotic association of a fungus with an alga or a cyanobacterium, or both. The fungal component of a lichen absorbs water and nutrients from the surroundings and provides a suitable environment for the alga or cyanobacterium. These live protected among the dense fungal hyphae and produce carbohydrates for the fungus by photosynthesis. Owing to this partnership, lichens can thrive in harsh environments such as mountaintops and polar regions. The more familiar lichens grow slowly as crusty patches, but lichens are found in a variety of forms, such as the tall, plantlike reindeer moss. The association between the different organisms in a lichen is so close that lichens are routinely referred to as a single organism, and scientists classify lichens using the name of the fungal component.

(Definitions from: American Heritage Science Dictionary)

Growth Habit

Intro paragraph to be provided by New York.

Vine:	DESCRIPTION TO BE PROVIDED BY NEW YORK.
Shrub:	DESCRIPTION TO BE PROVIDED BY NEW YORK.
Tree:	DESCRIPTION TO BE PROVIDED BY NEW YORK.
Et cetera:	DESCRIPTION TO BE PROVIDED BY NEW YORK.

State Rank

This numeric rank provides the relative rarity for each species based on a scale from 1 (very rare) to 5 (common). These ranks carry no legal status.

S1 - Typically 5 or fewer occurrences, very few remaining individuals, acres, or miles of stream, or some factor of its biology making it especially vulnerable in New York State.
S2 - Typically 6 to 20 occurrences, few remaining individuals, acres, or miles of stream, or factors demonstrably making it very vulnerable in New York State.
S3 - Typically 21 to 100 occurrences, limited acreage, or miles of stream in New York State.
S4 - Apparently secure in New York State.
S5 - Demonstrably secure in New York State.
SE - State exotic or non-native
SH - Historically known from New York State, but not seen in the past 15 years.
SNA - Species for which a rank is not applicable. This is mainly those species which are now excluded from flora for various reasons.
SNR - Not yet ranked
SX - Apparently extirpated from New York State.

Global Rank

Each species' global rank is determined by NatureServe. These ranks carry no legal weight. The global rank reflects the species worldwide rarity.

G1 - Critically Imperiled — At very high risk of extinction or elimination due to very restricted range, very few populations or occurrences, very steep declines, very severe threats, or other factors.
G2 - Imperiled — At high risk of extinction or elimination due to restricted range, few populations or occurrences, steep declines, severe threats, or other factors.
G3 - Vulnerable — At moderate risk of extinction or elimination due to a fairly restricted range, relatively few populations or occurrences, recent and widespread declines, threats, or other factors.
G4 - Apparently Secure — At fairly low risk of extinction or elimination due to an extensive range and/or many populations or occurrences, but with possible cause for some concern as a result of local recent declines, threats, or other factors.
G5 - Secure — At very low risk of extinction or elimination due to a very extensive range, abundant populations or occurrences, and little to no concern from declines or threats.
GH - Possibly Extinct — Known from only historical occurrences but still some hope of rediscovery. Examples of evidence include (1) that a species has not been documented in approximately 20-40 years despite some searching and/or some evidence of significant habitat loss or degradation; (2) that a species has been searched for unsuccessfully, but not thoroughly enough to presume that it is extinct or eliminated throughout its range.
GNA - Not Applicable — A conservation status rank is not applicable because the species is not a suitable target for conservation activities. A global conservation status rank may be not applicable for several reasons, related to its relevance as a conservation target. Typically the species is a hybrid without conservation value, or of domestic origin.
GNR - Global rank not yet assessed.
GX - Presumed Extinct — Not located despite intensive searches and virtually no likelihood of rediscovery.

Filter by County - Counties to Include - ANY versus ALL

Any - An Any search will combine the list of counties to include with a Boolean Or. Plant species returned will be found within at least one of the selected counties.
All - An All search will combine the list of counties to include with a Boolean And. Plant species returned will be found within each of the selected counties.

Filter by County - Counties to Exclude - ANY versus ALL

Any - An Any search will combine the list of counties to exclude with a Boolean Or. Plant species returned will not be found within at least one of the selected counties.
All - An All search will combine the list of counties to exclude with a Boolean And. Plant species returned will not be found within any of the selected counties.

Associated Ecological Communities

View a List of All Ecological Communities

For more information, contact: David Werier or Kyle Webster

Web Development: USF Water Institute

A member of the University of South Florida family of PlantAtlas.org sites

Citation Information:

Werier, David, Kyle Webster, Troy Weldy, Andrew Nelson, Richard Mitchell†, and Robert Ingalls†. 2026 New York Flora Atlas. [S. M. Landry and K. N. Campbell (original application development), USF Water Institute. University of South Florida]. New York Flora Association, Albany, New York.

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Definition: Vouchered Specimen

A voucher specimen is a pressed and thoroughly dried plant sample deposited in a herbarium, and is intended to be a permanent record supporting research purposes. A voucher may be a record of a plant's occurrence in a particular area, or a specific example of a plant used in a scientific investigation.

Proper vouchers display all the necessary attributes for complete identification of the plant, and are to be accompanied by accurate locality, habitat, collection time, and collector data.

Only plant populations vouchered by specimens deposited in Index Herbariorum (http://sweetgum.nybg.org/science/ih/) recognized herbaria are represented on this map.

Erigeron canadensis var. canadensis

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Classification

Citation

Source

Synonyms