# horseweed

*Erigeron canadensis*

Horseweed was the first weed species to document widespread evolutionary resistance to the common herbicide glyphosate (Roundup).

- **Taxonomy:** Plantae › Tracheophyta › Magnoliopsida › Asterales › Asteraceae › Erigeron
- **IUCN Red List status:** Least Concern
- **Population trend:** increasing
- **Biome:** urban
- **Habitat:** Disturbed soils, agricultural fields, roadsides, railways, and urban vacant lots.
- **Diet:** Photosynthetic (sunlight, water, carbon dioxide, and soil minerals).
- **Range:** North America, Europe, Asia, South America, Australia
- **Size:** 10 cm to 2 meters (0.3 to 6.5 feet) in height
- **Lifespan:** 1 year (annual or winter annual)
- **Active:** diurnal
- **Threats:** Intensive agricultural tilling and targeted mechanical weeding, though it is highly resilient.
- **Safe to approach?:** Harmless. This plant is safe to approach and handle, though its foliage contains essential oils that can cause mild contact dermatitis or skin irritation in sensitive individuals. Wash skin with soap and water if contact occurs.

## About

Erigeron canadensis (synonym Conyza 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.

## Sources

- Plate: https://gaia-dex.com/species/a8002081-a026-4e3f-9def-e3fb665aa93b
- iNaturalist: https://www.inaturalist.org/taxa/76907
- Wikipedia: https://en.wikipedia.org/wiki/Erigeron canadensis
- Conservation status: IUCN Red List category, as recorded by Gaia-Dex
- Photo: https://inaturalist-open-data.s3.amazonaws.com/photos/93166894/medium.jpeg (Zihao Wang, CC-BY, via iNaturalist)

Habitat, diet, size and similar notes are AI-written summaries; check them against the linked sources before relying on them.