Pediocactus simpsonii (Simpson's Hedgehog Cactus)

Plate 1 figs. a–h · 8 separate observations

Pediocactus simpsonii, photographed by Grant Chovil — fig. a Grant Chovil, CC BY 4.0 / 2022-05-19 / obs. 199029110

Pediocactus simpsonii, photographed by Jared Shorma — fig. b Jared Shorma, CC BY 4.0 / obs. 197894563

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 9 botanical countries

Native distribution of Pediocactus simpsonii, 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.

Region	TDWG code	Continent
Arizona	ARI	NORTHERN AMERICA
Colorado	COL
Idaho	IDA
Montana	MNT
Nevada	NEV
New Mexico	NWM
South Dakota	SDA
Utah	UTA
Wyoming	WYO

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 210 in flower of 400 examined

40%

77%

38%

Proportion of examined Pediocactus simpsonii in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	0	too few examined
Feb	0	1	too few examined
Mar	6	15	40%	20% to 64%
Apr	79	103	77%	68% to 84%
May	81	105	77%	68% to 84%
Jun	42	111	38%	29% to 47%
Jul	1	11	9%	2% to 38%
Aug	0	11	0%	0% to 26%
Sep	1	35	3%	1% to 15%
Oct	0	3	too few examined
Nov	0	3	too few examined
Dec	0	2	too few examined

Peak flowering in May. Each bar is the share of Pediocactus simpsonii 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. 210 of 400 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 5 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 2,069 observations

Condition	5th percentile	Median	95th percentile
Coldest month, mean daily low	-16.1 °C	-11.2 °C	-8.1 °C
Warmest month, mean daily high	21.2 °C	25.2 °C	30.4 °C
Annual rainfall	244 mm	452 mm	588 mm
Rainfall in the driest quarter	32 mm	61 mm	102 mm

It is found where winters are severely cold. This is not care advice and it is not a forecast. It is a measurement: we sampled the climate at every one of the 2,069 research-grade observations of Pediocactus simpsonii 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 31 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.

Echinocactus simpsonii Engelm.
Echinocactus simpsonii f. minor (Engelm.) Schelle
Echinocactus simpsonii var. minor Engelm.
Echinocactus simpsonii var. robustior J.M.Coult.
Mammillaria purpusii K.Schum.
Mammillaria simpsonii (Engelm.) M.E.Jones
Mammillaria spaethiana Späth
Pediocactus hermannii W.T.Marshall
Pediocactus nigrispinus subsp. indranus (Hochstätter) Hochstätter
Pediocactus robustior (J.M.Coult.) Arp
Pediocactus simpsonii f. acklinii Hochstätter
Pediocactus simpsonii f. campestris Hochstätter
Pediocactus simpsonii f. dinosauriensis Hochstätter
Pediocactus simpsonii f. flaminggorgensis Hochstätter
Pediocactus simpsonii f. flinspachii Hochstätter
Pediocactus simpsonii f. kuenzleri Hochstätter
Pediocactus simpsonii f. montanensis Hochstätter
Pediocactus simpsonii f. muehlii Hochstätter
Pediocactus simpsonii f. prairie Hochstätter
Pediocactus simpsonii f. sandiamontanus Hochstätter
Pediocactus simpsonii subsp. bensonii Hochstätter
Pediocactus simpsonii subsp. idahoensis Hochstätter
Pediocactus simpsonii subsp. indranus (Hochstätter) Hochstätter
Pediocactus simpsonii subsp. robustior (J.M.Coult.) Hochstätter

and 7 more.

Sourcesevery claim on this page

World Flora Online Plant List. accepted name, authority, classification. CC0. Retrieved 2026-07-12.
iNaturalist. photographs and flowering annotations, CC0 / CC BY / CC BY-SA only. per photograph. Retrieved 2026-06-27.
Wikidata. common name (P1843), joined on the World Flora Online identifier (P7715). CC0. Retrieved 2026-07-13.
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.