Conyza canadensis

"Notes: Western Ghats, Naturalized, Native of North America"

This native annual plant is 1-7' tall and unbranched, except for the flowering stems near the apex. The stout central stem is ridged and covered with long white hairs. The leaves alternate all around this stem (appearing almost whorled) and differ little in length, except beneath the inflorescence, creating a columnar effect. They are about 3-4" long and ½" across, narrowly lanceolate or oblanceolate, with a few teeth toward the outer tips, and fine white hairs along their margins. The smaller leaves near the inflorescence are more linear and less likely to have any teeth. When mature, several flowering stems appear at the apex, which branch frequently and spread upward and outward, terminating in a multitude of tiny composite flowers. These composite flowers are individually less than 1/8" across, but subtended by smooth green bracts that are somewhat longer. In each composite flower, there are numerous yellow disk florets in the center, which are surrounded by tiny white ray florets that remain erect, rather than spreading outward. There is no noticeable floral scent. The blooming period can occur any time from mid-summer to the fall, lasting about 2-3 weeks for individual plants. The small slender achenes are light brown and have tufts of white or light brown hair. Seed distribution is by wind. The root system consists of a branching taproot.

Initially, Horseweed may appear to be a tall, columnar goldenrod with hairy stems, and leaves that tend to angle upward from their bases. However, it dull inflorescence sets it apart. Upon close inspection, the tiny flowers have some resemblance to the more attractive flowers of the Erigeron spp. (Fleabanes), to which genus this plant was assigned in the past. Return

Erect annual herb. Stems simple or sparingly-branched, up to 1.2 m. Leaves linear to linear-lanceolate. Inflorescence a large terminal compound panicle. Capitula numerous, small, funnel-shaped with minute white ray-florets and yellow disk-florets.

canadensis: of Canada

"Karnataka: Mysore Tamil Nadu: Dindigul, Nilgiri, Theni"

"

Global Distribution

India, Nepal, Pakistan and North America

Indian distribution

State - Kerala, District/s: Kottayam, Kollam, Pathanamthitta, Palakkad, Thiruvananthapuram, Kozhikkode, Wayanad, Idukki

"

"Kerala: Kollam, Kottayam, Kozhikode, Palakkad, Pathanamthitta, Thiruvananthapuram"

Horseweed is a very common plant that occurs in every county of Illinois (see Distribution Map). In black soil prairies, it may appear in dry disturbed areas, particularly near the margins of more developed areas, such as fields. It can also be found in dry disturbed areas of gravel prairies, clay prairies, hill prairies, clay banks along rivers, and meadows near woodlands. In more developed areas, Horseweed often appears in abandoned fields, pastures, fence rows, vacant lots, garbage dumps, areas along railroads and roadsides, or in gardens and lawns. This plant is more common in disturbed areas. It has become an adventive weed in Europe.

Sinai.

Native to north and south America, widely naturalized in temperate regions.

Erigeron canadensis var. pusillus (Nutt.) B. Boivin:
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Erigeron canadensis var. glabratus A. Gray:
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Erigeron canadensis var. canadensis :
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Leptilon pusillum (Nutt.) Britton:
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Leptilon canadense (L.) Britton:
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Erigeron pusillus Nutt.:
Honduras (Mesoamerica)
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Conyza canadensis var. canadensis :
Argentina (South America)
Australia (Oceania)
Belize (Mesoamerica)
Bolivia (South America)
Brazil (South America)
Canada (North America)
Chile (South America)
Colombia (South America)
Costa Rica (Mesoamerica)
Ecuador (South America)
United States (North America)
Mexico (Mesoamerica)
Guatemala (Mesoamerica)
El Salvador (Mesoamerica)
Panama (Mesoamerica)
Venezuela (South America)
Peru (South America)
Uruguay (South America)
Paraguay (South America)
Caribbean (Caribbean)
New Zealand (Oceania)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Conyza parva Cronquist:
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Conyza canadensis var. pusilla (Nutt.) Cronquist:
Belize (Mesoamerica)
Costa Rica (Mesoamerica)
El Salvador (Mesoamerica)
Guatemala (Mesoamerica)
Honduras (Mesoamerica)
Mexico (Mesoamerica)
Nicaragua (Mesoamerica)
Panama (Mesoamerica)
United States (North America)
Caribbean (Caribbean)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Conyza canadensis var. glabrata (A. Gray) Cronquist:
Canada (North America)
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Conyza canadensis (L.) Cronquist:
Argentina (South America)
Australia (Oceania)
Belize (Mesoamerica)
Bolivia (South America)
Brazil (South America)
Canada (North America)
Mexico (Mesoamerica)
Honduras (Mesoamerica)
Costa Rica (Mesoamerica)
Guatemala (Mesoamerica)
Colombia (South America)
Ecuador (South America)
El Salvador (Mesoamerica)
French Guiana (South America)
Nicaragua (Mesoamerica)
Chile (South America)
New Zealand (Oceania)
United States (North America)
Panama (Mesoamerica)
South Africa (Africa & Madagascar)
Suriname (South America)
Venezuela (South America)
Peru (South America)
Uruguay (South America)
Paraguay (South America)
Caribbean (Caribbean)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Erigeron canadensis L.:
Bolivia (South America)
Honduras (Mesoamerica)
Canada (North America)
United States (North America)
China (Asia)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Originating from temperate North America, but now a widespread weed.

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Canada

Origin: Exotic

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

United States

Origin: Unknown/Undetermined

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

A cosmopolitan weed of N. American origin.

Plants erect, (3–)50–200(–350+) cm, branched mostly distally. Leaves: faces usually glabrate (proximal margins ± ciliolate, hairs usually stiff, spreading and hispid on nerves, hairs erect); proximal blades oblanceolate to linear, 20–50(–100+) × 4–10(–15+) mm, toothed to entire; distal similar, smaller, entire. Heads usually in paniculiform, sometimes corymbiform arrays. Involucres 3–4 mm. Phyllaries usually glabrous, sometimes sparsely strigose (margins chartaceous to scarious); outer greenish to stramineous, lanceolate to linear, shorter; inner stramineous to reddish, lance-attenuate to linear. Receptacles 1–1.5(–3) mm diam. in fruit. Pistillate florets 20–30(–45+); corollas ± equaling or surpassing styles, laminae 0.3–1 mm. Disc florets 8–30+. Cypselae uniformly pale tan to light gray-brown, 1–1.5 mm, faces sparsely strigillose; pappi of 15–25, white bristles 2–3 mm. 2n = 18.

450-2500 m

"Slender erect herbs, 50 cm to more than 2 m in height, nearly smooth or bristly hairy, unbranched at base, branched near top with many small flower heads. Leaves alternate, often appearing opposite, basal and lower stem leaves 2.5 - 10 x 1 cm, strap-shape, entire or toothed, medium and upper stem leaves smaller, sessile, entire, very narrow, soft hairy at first but becoming harsh on older leaves. Flower heads small, numerous on many short branches at top of stem, about 5 mm in diameter; involucre of 2 or 3 series of very small, pointed, greenish bracts 2.5 to 5 mm long; receptacle flat, 1.2 to 2.5 mm broad when bare. Ray florets very short, usually concealed by slightly longer involucral bracts around each flower, greenish white to lavender, pistillate, more than 100 per head, about as long as disk florets; disk florets numerous, bisexual. Achene, cylindrical, elongated, broadest above the middle, somewhat tapering toward scar that has attached light-colored collar, apex truncate, surface is longitudinally grooved and has scattered white hairs, 1.3 x 0.3 mm, pappus of 10 or up to 200 hairs, brownish yellow, 1.5 to 3 times longer than achene."

Erigeron canadensis Linnaeus, Sp. Pl. 2: 863. 1753 (as canadense); Conyza canadensis var. glabrata (A. Gray) Cronquist; C. canadensis var. pusilla (Nuttall) Cronquist; C. parva Cronquist; E. canadensis var. pusillus (Nuttall) B. Boivin

Horseweed is a very common plant that occurs in every county of Illinois (see Distribution Map). In black soil prairies, it may appear in dry disturbed areas, particularly near the margins of more developed areas, such as fields. It can also be found in dry disturbed areas of gravel prairies, clay prairies, hill prairies, clay banks along rivers, and meadows near woodlands. In more developed areas, Horseweed often appears in abandoned fields, pastures, fence rows, vacant lots, garbage dumps, areas along railroads and roadsides, or in gardens and lawns. This plant is more common in disturbed areas. It has become an adventive weed in Europe.

Waste ground, edges of cultivation.

Wasps and flies are the most common visitors of the flowers, where they seek nectar. Among the wasp visitors, this includes Sphecid wasps, Vespid wasps, and Ichneumonid wasps. Among the flies, this includes Syrphid flies, Thick-headed flies, Tachinid flies, Flesh flies, Blow flies, and Muscid flies. A few small bees may also visit the flowers. Fertile seed can be produced without cross-pollination. Some insects have been observed feeding on this plant, including the caterpillars of Agrapha oxygramma (Sharp-Stigma Loop Moth), and Nysius niger (Black Seed Bug). Mammalian herbivores usually leave this plant alone because the foliage is bitter. Rabbits may eat the tops off of young plants occasionally. The ecological value of this plant to wildlife is low, except to some flower-visiting insects.

Conyza canadensis (Horseweed)
(Bees collect pollen or suck nectar; flies feed on pollen or suck nectar; other insects suck nectar; some observations are from Robertson, otherwise they are from Graenicher, Moure & Hurd, and Krombein et al. as indicated below)

Bees (long-tongued)
Anthophoridae (Epeolini): Epeolus pusillus sn

Bees (short-tongued)
Halictidae (Halictinae): Agapostemon sericea sn (Gr), Augochlorella striata sn (Gr), Halictus ligatus (MH), Halictus sp. (Lasioglossum sp.) sn (Gr), Halictus rubicunda sn (Gr), Lasioglossum albipennis sn (Gr), Lasioglossum cinctipes sn (Gr), Lasioglossum connexus sn cp (Gr), Lasioglossum coriaceus sn (Gr), Lasioglossum imitatus sn cp (Gr), Lasioglossum pilosus pilosus sn (Gr), Lasioglossum tegularis sn cp (Gr), Lasioglossum versatus sn cp (Rb, Gr), Lasioglossum zephyrus sn (Gr); Halictidae (Sphecodini): Sphecodes prosphorus sn (Gr); Colletidae (Hylaeinae): Hylaeus mesillae (Kr); Andrenidae (Panurginae): Calliopsis andreniformis cp (Kr)

Wasps
Sphecidae (Crabroninae): Anacrabro ocellatus, Ectemnius dives (Gr), Ectemnius lapidarius (Gr), Lestica confluentus (Gr), Lestica producticollis (Gr); Sphecidae (Larrinae): Larra analis (Gr), Tachytes distinctus; Sphecidae (Philanthinae): Cerceris clypeata (Rb, Gr), Cerceris deserta (Gr), Eucerceris fulvipes (Gr), Eucerceris zonata; Vespidae: Dolichovespula arenaria (Gr), Polistes fuscata; Vespidae (Eumeninae): Ancistrocerus adiabatus (Rb, Gr), Eumenes fraterna (Gr), Euodynerus foraminatus (Gr), Stenodynerus anormis (Gr), Symmorphus cristatus (Gr); Chrysididae: Ceratochrysis perpulchra (Gr); Perilampidae: Perilampus hyalinus sn fq (Gr); Gasteruptiidae: Gasteruption tarsatorius (Gr); Ichneumonidae: Ceratogastra ornata

Flies
Syrphidae: Allograpta obliqua (Gr), Eristalis tenax sn, Paragus bicolor (Gr), Sphaerophoria contiqua (Gr), Syritta pipiens sn (Rb, Gr), Toxomerus geminatus (Gr), Toxomerus marginatus sn (Rb, Gr); Conopidae: Thecophora occidensis sn; Tachinidae: Cylindromyia dosiades (Gr), Cylindromyia fumipennis sn, Leucostoma simplex (Gr); Sarcophagidae: Helicobia rapax (Gr), Sarcophaga sp. (Gr), Sarcophaga sarracenioides (Gr), Sphixapata trilineata sn; Anthomyiidae: Delia platura (Gr); Calliphoridae: Pollenia rudis sn; Muscidae: Musca domestica sn, Neomyia cornicina sn; Sciaridae: Sciara fuliginosus (Gr); Tephritidae: Euraresta bella (Gr); Agromyzidae: Melanagromyza aeneoventris (Gr)

Beetles
Coccinellidae: Coccinella novemnotata sn (Gr)

Plant Bugs
Miridae: Adelphocoris rapidus (Gr), Cimex ruficornis (Gr), Lygus lineolaris (Gr), Metriorrhynchomiris dislocatus (Gr), Plagiognathus sp. (Gr); Thyreocoridae: Corimelaena pulicarius (Gr)

In Great Britain and/or Ireland:
Foodplant / parasite
sporangium of Basidiophora entospora parasitises live Conyza canadensis

Foodplant / sap sucker
adult of Neides tipularius sucks sap of Conyza canadensis

Foodplant / feeds on
larva of Olibrus corticalis feeds on Conyza canadensis

Foodplant / parasite
cleistothecium of Podosphaera fusca parasitises live Conyza canadensis

Hyalites rahira rahira (Marsh acraea)

Frequent

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 5
Specimens with Barcodes: 32
Species With Barcodes: 1

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 4
Species With Barcodes: 1

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: T5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Canada

Rounded National Status Rank: NNA - Not Applicable

United States

Rounded National Status Rank: NNR - Unranked

Rounded Global Status Rank: T4 - Apparently Secure

Reasons: Occurs throughout western North America.

Rounded Global Status Rank: T5 - Secure

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

These species are introduced in Switzerland.

The preference is full sun, moist to dry conditions, and rich fertile soil. However, this plant flourishes in other kinds of soil, including those containing considerable amounts of gravel and clay. This weedy plant is easy to grow, and sometimes forms large colonies in favorable disturbed sites. Drought resistance is very good.