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Conyza canadensis

(Canada Horseweed)

Overview

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Interesting Facts

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Common Names

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Click on the language to view common names.

Common Names in English:

Canada Horseweed, Butterweed, Canadian Horseweed, Canadian-Fleabane, Dwarf Horseweed, Fleabane, Hogweed, Horseweed, Horseweed Fleabane, Mares Tail, Marestail

Common Names in French:

Vergerette Du Canada

Common Names in German:

Kanadisches Berufkraut

Description

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Genus Conyza

Annuals [perennials ], 10-120(-350+) cm. Stems usually erect , branched mostly distally (spreading and branched throughout in C. ramosissima), glabrous or hispid , hispidulous , strigillose , or strigose . Leaves basal and cauline (mostly cauline at flowering) ; alternate; petiolate or sessile; blades mostly lanceolate to oblanceolate or linear , margins rarely lobed , ultimate toothed or entire, faces usually hispid, hispidulous, strigillose, or strigose (eglandular ). Heads radiate or disciform , usually in spreading to strict , paniculiform or corymbiform arrays (borne ± singly in C. ramosissima). Involucres ± turbinate , 2-5[-7+] mm diam. Phyllaries 20-40+ in 2-4 series, appressed (usually reflexed in fruit), the larger usually 3-nerved (midnerves orange to brownish; not notably keeled ), lanceolate to linear, unequal, ± herbaceous medially, margins membranous, abaxial faces glabrous or hirsutulous , hispidulous, or strigose. Receptacles ± flat, pitted or smooth , epaleate. Peripheral ("ray") florets pistillate , fertile : either 20-45+ in 1-2+ series, corollas white to purplish (filiform with laminae filiform to elliptic , 0.1-1[-1.5+] mm), or 20-150+ in 2-5+ series, corollas ochroleucous (filiform, laminae lacking, distally truncate or 2-5-toothed). Disc florets 3-30+, bisexual , fertile; corollas yellowish (nerves sometimes prominently resinous ), tubes shorter than narrowly funnelform throats , lobes 5, erect or spreading, deltate; style-branch appendages deltate. Cypselae compressed , oblong to elliptic, 1-nerved on each edge , faces glabrous or strigillose (hairs 0.05-0.1+ mm), eglandular; pappi persistent , of 15-25+ pinkish, sordid , tawny , or white, ± equal, barbellulate , apically attenuate bristles in 1 series. x = 9.

Species 25-40+: widespread, mostly in subtropical and warm-temperate zones.

Distinctions between Conyza and Erigeron, as usually circumscribed in the past 50+ years, are not always clear. Usually, conyzas have unequal (graduated ) phyllaries and 2-20+ times as many pistillate florets as bisexual florets in each head (rarely more bisexual than pistillate), and corollas of pistillate florets either lack laminae or have laminae usually less than 1(-1.5) mm. Erigerons usually have subequal phyllaries and more bisexual than pistillate florets (rarely more pistillate than bisexual) and corollas of pistillate florets (if any) usually have laminae 2-10+ mm.

In studies by R. D. Noyes (2000) and by Noyes and L. H. Rieseberg (1999), Conyza, as traditionally circumscribed, was found to be nested within Erigeron and to be para- and/or polyphyletic. Here, absent an alternate taxonomy, four species traditionally treated in Conyza are retained in Conyza and a separate suite of six species that have usually been included in Conyza are treated in Laënnecia.[1]

Physical Description

Species Conyza canadensis

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. [source]

Plants with stems glabrous and phyllaries red-tipped are sometimes treated as var. pusilla; similar plants with stems glabrous and phyllaries stramineous (not red-tipped) are sometimes treated as var. glabrata. [source]

Habit: Forb/herb • Growth Form: Single Crown • Shape and Orientation: Erect

Flowers: Bloom Period: January, February, March, April, May, June, July, August, September, October, November, December. • Flower Color: White • Flower Conspicuous: Yes

Seeds: Seed per Pound: 700000 • Seed Spread Rate: Rapid • Seedling Vigor: High • Fruit/Seed Abundance: High • Fruit/Seed Color: Brown • Fruit/Seed Conspicuous: No • Cold Stratification Required: No

Foliage: Foliage Color: Green • Foliage Porosity Summer: Porous • Foliage Porosity Winter: Porous • Foliage Texture: Coarse • Fall Conspicuous: No • Leaf Retention: No

Size/Age/Growth

Active Growth Period: Spring , Summer, Fall • Growth Rate: Rapid • After Harvest Regrowth Rate: Slow • Mature Height (feet): 5.0 • Size: 12-18" tall. • Vegetative Spread Rate: None • Lifespan: Lifespan

Habitat

Disturbed places; 0-2000 m [2].

Typically found at an altitude of 0 to 4,653 meters (0 to 15,266 feet).[3]

Biology

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Reproduction

Duration: Annual , Biennial • Coppice Potential: No • Progagated by Bulbs: No • Propagated by Bare Root: No • Propagated by Container: No • Propagated by Corms: No • Propagated by Cuttings: No • Propagated by Seed: Yes • Propagated by Sod: No • Propagated by Sprigs: No • Propagated by Tubers: No • Fruit/Seed Persistence: No

Growth

Culture: Space 24-36" apart.

Soil: Adapted to Medium Textured: Adapted to Medium Textured Soils • Adapted to Coarse Textured Soils: Yes • Anaerobic Tolerance: Low • Salinity Tolerance: None • CaCO3 Tolerance: Low • Minimum pH: 4.8 • Maximum pH: 7.2 • Fertility Requirement: Medium

Sunlight: Sun Exposure: Full Sun . • Shade Tolerance: Intolerant

Moisture: Drought Tolerance: Low • Minimum Precipitation: 14 • Maximum Precipitation: 55 • Moisture Use: Medium

Temperature: Minimum Temperature (F): 52 • Minimum Frost Free Days: 60

Taxonomy

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Synonyms

C. canadensis var. pusilla (Nuttall) Cronquist • C. parva Cronquist • Conyza canadensis var. glabrata (A. Gray) Cronquist • E. canadensis var. pusillus (Nuttall) B. Boivin • Erigeron canadensis Linnaeus

Notes

Name Status: Accepted Name .

Comment: Data Providers: Biological Diversity of the Guiana Shield , CONABIO, Caribbean Checklist , African Flowering Plants Database , SANBI, New Zealand Plant Name Database, Flora of Japan, Flora Malesiana, Flora of Taiwan, LCR Editor, Govaerts World Compositae Ch. GCC LSID: urn :lsid:compositae.org:names:44AAE4D8-3715-414A-8CE4-84FEF16F6C9F

Last scrutiny: 02-Nov-09

Similar Species

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Members of the genus Conyza

ZipcodeZoo has pages for 16 species, subspecies, varieties, forms, and cultivars in this genus:

C. albida (Broad-Leaved Fleabane) · C. anthelmintica (Ironweed) · C. apurensis (Manzanilla Horseweed) · C. balsamifera (Nagi Camphor) · C. bilbaoana (Fleabane) · C. bonariensis (Asthmaweed) · C. bonariensis var. bonariensis (Asthmaweed) · C. britannica (Xuan Fu Hua) · C. canadensis (Canada Horseweed) · C. canadensis var. canadensis (Canadian Horseweed) · C. canadensis var. glabrata (Canadian Horseweed) · C. canadensis var. pusilla (Canadian Horseweed) · C. floribunda (Asthmaweed) · C. primulifolia (Primroseleaf Horseweed) · C. ramosissima (Branching Conyza) · C. sagittalis (Wingstem Camphorweed)

More Info

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Further Reading

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Notes

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Contributors

Data Sources

Accessed through GBIF Data Portal November 17, 2007:

Identifiers

Footnotes

  1. John L. Strother "Conyza". in Flora of North America Vol. 20 Page 3, 9,11, 36, 257, 348, 349. Oxford University Press. Online at EFloras.org. [back]
  2. "Conyza canadensis". in Flora of North America Vol. 20 Page 347,349, 350. Oxford University Press. Online at EFloras.org. [back]
  3. Mean = 185.870 meters (609.810 feet), Standard Deviation = 277.330 based on 8,019 observations. Altitude information for each observation from British Oceanographic Data Centre. [back]
Last Revised: 7/15/2012