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Asteraceae family

Canadian Horseweed Conyza canadensis

Native
Late-season nectar — Flowers in a late-autumn window when few other plants in our catalog bloom — valuable late forage for pollinators (relative to our catalog's bloom coverage).
Also known as: canadian fleabane

Canadian Horseweed is an annual wildflower native to Canada, the lower 48 states, and U.S. outlying islands. It grows to 5 ft and blooms Jul – Oct in part shade – shade, with brown fruit.

More about this plant

Erigeron canadensis is an annual plant native throughout most of North America and Central America. It is also widely naturalized in Eurasia and Australia. Common names include horseweed, Canadian horseweed, Canadian fleabane, coltstail, marestail, and butterweed. It was the first weed to have developed glyphosate resistance, reported in 2001 from Delaware. Wikipedia →

Growing & care

USDA PLANTS · TRY
Conditions
Sources · Conditions
USDA PLANTS — Sun · Soil & moisture
USDA — SoilPH — Soil pH
USDA PLANTS (DwCA, Zenodo 17903503) — Fertility Requirement / Soil Adaptation — Fertility need · Adapts to
USDA — Temp-Min °F — Hardiness
Sun
Part shade – shade
Soil & moisture
Medium moisture
Soil pH
4.8–7.2
Fertility need
Medium
Adapts to
Coarse (sandy), Medium (loam), Fine (clay)
Hardiness
USDA zone 13+
Size & form
Sources · Size & form
USDA PLANTS (DwCA, Zenodo 17903503) — Height, Mature — Height
USDA PLANTS (DwCA, Zenodo 17903503) — Growth Rate / Spread / Growth Form / Lifespan / Active Growth Period / Seed Period — Spread · Growth rate · Growth form · Active growth
USDA PLANTS — Lifespan
TRY Plant Trait Database (CC BY 4.0) · USDA PLANTS — Foliage
USDA PLANTS (DwCA, Zenodo 17903503) — Fruit/Seed Color / Fruit Persistence — Fruit
Height
5 ft
Spread
None — clumping
Growth rate
Rapid
Growth form
Single crown
Lifespan
Annual
Foliage
Broadleaf · coarse texture
Active growth
Spring through autumn
Fruit
Brown
In the garden
Sources · In the garden
USDA PLANTS (DwCA, Zenodo 17903503) — Propagation Method / Commercial Availability — Propagate by · In the trade
USDA PLANTS (DwCA, Zenodo 17903503) — Germination (cold stratification) — Seed starting
USDA PLANTS (DwCA, Zenodo 17903503) — Foliage Texture / Browse Palatability / Resprout — Resprouts if cut
Propagate by
Seed
Seed starting
No stratification needed
In the trade
No known commercial source
Resprouts if cut
No
Shrub layer — Sits in the shrub of a layered food forest or polyculture.Open guide →
derived roles
The garden year bloom → fruit → fall colour
J
F
M
A
M
J
J
A
S
O
N
D
Bloom
Bloom (the flower's colour)
Bloom · Jul – Oct — 1,520 obs · Herbarium specimens — Park et al. 2023 (CC BY 4.0)
When to sow · for your area

Sow timing keys off your local last- and first-frost dates.

Species characteristics from USDA PLANTS (public domain) + TRY (CC BY) — general guidance, not a guarantee for your exact site. Deer "browsing" is documented palatability, not a deer-proof claim.

Wildlife & pollinators

How pollinator value is scored →
❧ Caterpillar hosts ~11 caterpillar species

Conyza supports ~11 caterpillar species.

Native butterfly & moth caterpillars are the base of the terrestrial food web — most songbirds rear their young almost entirely on them. As a host for native Lepidoptera this is a moderate genus.

Recorded feeding on Conyza in North America, including:

Charidryas nycteis · brush-footed butterfly ✦ Chlorochlamys chloroleucaria · geometer (inchworm) moth ✦ Ctenoplusia oxygramma · Sharp-Stigma Looper Moth ✦ Cucullia florea · Gray Hooded-Owlet ✦ Cucullia speyeri · owlet moth ✦ Eupithecia miserulata · Common Eupithecia ✦
+ 5 more species →
Peridroma saucia · Pearly Underwing ✦ Sparganothis sulfureana · Sparganothis Fruitworm ✦ Spodoptera ornithogalli · Yellow-Striped Armyworm Moth ✦ Synchlora aerata · Wavy-Lined Emerald ✦ Thyridopteryx ephemeraeformis · Evergreen Bagworm Moth ✦
Keystone count (genus-level) from Warren II 2026 (CC0) · Tallamy host-use records. Named species (a documented Nearctic sample, not exhaustive) from NHM HOSTS (CC0). ✦ = recorded on this exact species.
Species thumbnails re-hosted from iNaturalist — Creative Commons, credited per image (hover for credit). Click any species to see it on iNaturalist. Not exhaustive; many taxa have no openly-licensed photo yet.
How we know this (1) Methods & honest limits
Photosynthesis Direct fact

A recorded categorical fact: each species is tagged C3 (standard), C4 (heat/water-efficient) or CAM (succulent, night-time CO₂ uptake) — or a facultative combination. We only show a trait card for the noteworthy C4/CAM cases; C3 is the unremarkable majority, kept in the data but not surfaced as a card.

Kattge, J. et al. TRY plant trait database — Categorical Traits Dataset (2012).
Derived values are computed from open data by a published method — labelled, cited, and never shown as a direct observation. Full methodology →
Sources for this entry (27) Open & cited
[01] Scientific name & family — USDA PLANTS (DwCA, Zenodo 17903503)
[02] Growth habit & duration — USDA PLANTS (DwCA, Zenodo 17903503)
[03] Native status & distribution — USDA PLANTS (DwCA, Zenodo 17903503)
[04] Common name — USDA PLANTS (via GBIF)
[16] Invasive / introduced status — US-RIIS v2.0 (USGS)
[18] Description — Wikipedia (CC BY-SA)
[19] Ecological value — Warren II 2026 (CC0) · Tallamy host-use counts
[21] Conservation rank — NatureServe Explorer (CC BY)
[23] Photosynthetic pathway — TRY Plant Trait Database (CC BY 4.0)
[25] Other common names — Wikidata (CC0)
[26] Caterpillar host count — Warren II 2026 (Dryad, CC0) · Tallamy host-use counts
[27] Caterpillar species — NHM HOSTS (CC0)
Spot an error or have a better photo? Every field links to its source, and the whole dataset is open.
Cite this page Open data, please attribute

PlantKey’s data is open under CC BY-SA 4.0 — free to reuse and adapt, with attribution and the same licence. Photos keep their own per-image licence + credit (see Sources above).

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