Erigeron primulifoliumJuss. ex Cass.

primroseleaf horseweed

WFO wfo-0000035490 Accepted WFO 2026-06 8 photographs CC0 / CC BY

Plate 1 figs. a–h · 8 separate observations

Erigeron primulifolium, photographed by Matthew Fainman
fig. a Matthew Fainman, CC BY 4.0 / 2021-12-13 / obs. 172552526

Every figure is a research-grade observation under CC0, CC BY or CC BY-SA, rehosted with the photographer’s name, the licence and the observation it came from. Photographs under a NonCommercial licence are excluded from this site and are never stored, which costs us a great many pictures and is not negotiable.

Native range 31 botanical countries

Regions where Erigeron primulifolium is native: Mexico Central, Mexico Gulf, Mexico Southeast, Argentina Northeast, Argentina Northwest, Argentina South, Bolivia, Brazil North, Brazil Northeast, Brazil South, Brazil Southeast, Brazil West-Central, Chile Central, Chile South, Colombia, Costa Rica, Dominican Republic, Ecuador, El Salvador, Guatemala, Guyana, Haiti, Honduras, Nicaragua, Panamá, Paraguay, Peru, Puerto Rico, Suriname, Uruguay, Venezuela Mexico CentralMexico GulfMexico SoutheastArgentina NortheastArgentina NorthwestArgentina SouthBoliviaBrazil NorthBrazil NortheastBrazil SouthBrazil SoutheastBrazil West-CentralChile CentralChile SouthColombiaCosta RicaDominican RepublicEcuadorEl SalvadorGuatemalaGuyanaHaitiHondurasNicaraguaPanamáParaguayPeruPuerto RicoSurinameUruguayVenezuela
Native distribution of Erigeron primulifolium, after Kew’s World Checklist of Vascular Plants. Introduced, extinct and doubtful records are excluded, so this is where the plant is from, not everywhere it now grows.
RegionTDWG codeContinent
Argentina Northeast AGE SOUTHERN AMERICA
Argentina Northwest AGW
Argentina South AGS
Bolivia BOL
Brazil North BZN
Brazil Northeast BZE
Brazil South BZS
Brazil Southeast BZL
Brazil West-Central BZC
Chile Central CLC
Chile South CLS
Colombia CLM
Costa Rica COS
Dominican Republic DOM
Ecuador ECU
El Salvador ELS
Guatemala GUA
Guyana GUY
Haiti HAI
Honduras HON
Nicaragua NIC
Panamá PAN
Paraguay PAR
Peru PER
Puerto Rico PUE
Suriname SUR
Uruguay URU
Venezuela VEN
Mexico Central MXC NORTHERN AMERICA
Mexico Gulf MXG
Mexico Southeast MXT

Region boundaries approximated from Natural Earth (public domain) and mapped to TDWG World Geographical Scheme for Recording Plant Distributions (WGSRPD) level-3 botanical countries (Brummitt 2001). Indicative, not the official WGSRPD geometry.

Flowering 31 in flower of 35 examined

Proportion of examined Erigeron primulifolium in flower, by month
Month In flower Examined Share 95% interval
Jan 8 9 89% 56% to 98%
Feb 1 1 too few examined
Mar 3 3 too few examined
Apr 1 1 too few examined
May 1 2 too few examined
Jun 0 0 too few examined
Jul 1 1 too few examined
Aug 0 1 too few examined
Sep 1 1 too few examined
Oct 3 3 too few examined
Nov 5 6 83% 44% to 97%
Dec 7 7 100% 65% to 100%

Peak flowering in Dec. Each bar is the share of Erigeron primulifolium observations in which someone actually recorded the reproductive state and found the plant in flower, not the raw number of flowering records. That distinction matters: people observe plants far more in spring than in winter, so a bare count of flowering records partly measures when people go outside. Dividing by the number examined removes that. 31 of 35 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 9 months have fewer than 5 examined observations, so no proportion is drawn for them. This is still a global aggregate and not a forecast for your garden: the same species flowers on different dates in different hemispheres. Where a species has fewer than 30 flowering records we do not draw this chart at all. Computed from 10.15468/dl.cgje2x.

Where it actually grows measured, from 232 observations

Condition 5th percentile Median 95th percentile
Coldest month, mean daily low 1.8 °C 7.7 °C 16.3 °C
Warmest month, mean daily high 22.5 °C 26.7 °C 30.5 °C
Annual rainfall 713 mm 1,115 mm 2,882 mm
Rainfall in the driest quarter 21 mm 121 mm 351 mm

It is found where winters are cool but frost is light or absent. This is not care advice and it is not a forecast. It is a measurement: we sampled the climate at every one of the 232 research-grade observations of Erigeron primulifolium that carry a coordinate, and this is the range those places actually span. The 5th and 95th percentiles are used rather than the minimum and maximum, because a single cultivated specimen in a heated conservatory should not widen a tropical plant's range to the Arctic.

This is not a hardiness zone. A USDA zone is the average annual extreme minimum temperature. The figure above is the mean daily minimum of the coldest month, which is a different quantity and is typically far warmer. Reading one as the other would place a plant several zones too warm, so we do not publish a hardiness zone, because we do not have one. Climate from CHELSA V2.1 (Karger et al. 2017); occurrences from 10.15468/dl.cgje2x.

Also published as 23 synonyms

A synonym is not an error. It is a record of botanists disagreeing, in print, about where this plant belongs. Each of these was somebody’s considered answer.

  • Conyza chilensis Spreng.
  • Conyza chilensis var. carnea Chodat
  • Conyza chilensis var. chilensis
  • Conyza chilensis var. guaranitica Chodat
  • Conyza chilensis var. integrifolia Phil.
  • Conyza chilensis var. monocephala DC.
  • Conyza diversifolia Weinm.
  • Conyza longifolia Desf.
  • Conyza myosotifolia Kunth
  • Conyza primulifolia (Lam.) Cuatrec. & Lourteig
  • Conyza scabiosifolia J.Rémy
  • Conyza yungasensis Rusby
  • Dimorphanthes procera Cass.
  • Erigeron chilensis (Spreng.) D.Don ex Loudon
  • Erigeron longifolius Baill.
  • Erigeron pinetorum Urb.
  • Erigeron primulifolius (Lam.) Greuter
  • Erigeron scabiosifolius (J.Rémy) Herter
  • Erigeron strictissimus Wender.
  • Erigeron sulcatus Meyen
  • Erigeron sulcatus var. sulcatus
  • Inula primulifolia Lam.
  • Marsea chilensis (Spreng.) V.M.Badillo

Sourcesevery claim on this page

  1. World Flora Online Plant List. accepted name, authority, classification. CC0. Retrieved 2026-07-12.
  2. iNaturalist. photographs and flowering annotations, CC0 / CC BY / CC BY-SA only. per photograph. Retrieved 2026-06-27.
  3. USDA PLANTS Database. common name, checklist symbol COPR5. public domain. Retrieved 2026-07-13.
  4. Kew, World Checklist of Vascular Plants (WCVP v16). native distribution by TDWG level-3 botanical country, and life form. CC BY 3.0. Retrieved 2026-06-04.

We publish what we can source and we say so when we cannot. This page has no care advice and no toxicity claim, because we do not yet have those from a source we can cite.