Ageratum houstonianumMill.

Plate 1 figs. a–h · 8 separate observations

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.

The specimen a real sheet, in a real collection

A real pressed plant, in a real collection, under the accession number above. Not an illustration of one. The holding institution does not serve this sheet’s image to third parties, so there is no photograph here. The record is real and the link goes to it. Where we hold no openly licensed sheet for a species this section is simply absent, and where a sheet never recorded who determined it, that field stays empty rather than being filled in. Roughly half of all herbarium sheets never recorded a determiner, which is ordinary.

Native range 9 botanical countries

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 1,055 in flower of 1,075 examined

Peak flowering in Jan. Each bar is the share of Ageratum houstonianum 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. 1,055 of 1,075 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 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 1,942 observations

It is barely found anywhere that freezes. This is not care advice and it is not a forecast. It is a measurement: we sampled the climate at every one of the 1,942 research-grade observations of Ageratum houstonianum 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.

Named cultivars 10 recorded

Selections of Ageratum houstonianum that somebody named and propagated. A cultivar is not a botanical taxon: it is governed by the cultivated-plant code rather than the botanical one, so it appears in no taxonomic backbone, and it has no native range and no wild population of its own. These get no page here, because a cultivar has no photographs, no range and no flowering data of its own, and a page with none of those is not a page.

• ‘ʽArtist Blue’’ Q110765923
• ‘ʽArtist Blue Violet’’ Q110765924
• ‘ʽArtist Purple’’ Q110765925
• ‘ʽBlue Blazer’’ Q110765926
• ‘ʽBlue Danube’’ Q110765927
• ‘ʽBlue Horizon’’ Q110765928
• ‘ʽBlue Mink’’ Q110765930
• ‘ʽBlue Puffs’’ Q110765931
• ‘ʽCloud Nine Blue’’ Q110765932
• ‘ʽCloud Nine White’’ Q110765933

From Wikidata (CC0), joined to this species on its World Flora Online identifier, so the link to the parent is exact rather than a name match. This list is what is recorded in an openly licensed register; it is not every cultivar that exists, and for many genera it is not close. Why, and how far short it falls.

Also published as 26 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.

• Ageratum conyzoides subsp. houstonianum (Mill.) Sahu
• Ageratum conyzoides subsp. houstonianum (Mill.) M.Sharma
• Ageratum conyzoides var. houstonianum (Mill.) T.R.Sahu
• Ageratum conyzoides var. mexicanum (Sims) DC.
• Ageratum houstonianum f. houstonianum
• Ageratum houstonianum f. isochroum B.L.Rob.
• Ageratum houstonianum f. luteum B.L.Rob.
• Ageratum houstonianum f. niveum B.L.Rob.
• Ageratum houstonianum f. normale B.L.Rob.
• Ageratum houstonianum f. versicolor B.L.Rob.
• Ageratum houstonianum var. angustatum B.L.Rob.
• Ageratum houstonianum var. houstonianum
• Ageratum houstonianum var. typicum B.L.Rob.
• Ageratum mexicanum Sweet
• Ageratum mexicanum Sims
• Ageratum mexicanum f. caeruleum Voss
• Ageratum mexicanum f. lasseauxii (Carrière) Voss
• Ageratum mexicanum f. mexicanum
• Ageratum mexicanum f. wendlandii Voss
• Ageratum mexicanum var. majus Voss
• Ageratum mexicanum var. mexicanum
• Ageratum mexicanum var. nanum Voss
• Ageratum wendlandii Hort. ex Vilm.
• Ageratum wendlandii Bailly

and 2 more.

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. Wikidata. common name (P1843), joined on the World Flora Online identifier (P7715). CC0. 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.