Acmispon tomentosus(Hook. & Arn.) Govaerts

Heermann's bird's-foot trefoil

WFO wfo-0001423501 Accepted WFO 2026-06 8 photographs CC0 / CC BY

Plate 1 figs. a–h · 8 separate observations

Acmispon tomentosus, photographed by Kyle Nessen
fig. a Kyle Nessen, CC0 1.0 / 2019-06-22 / obs. 42756561

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 2 botanical countries

Regions where Acmispon tomentosus is native: California, Mexico Northwest CaliforniaMexico Northwest
Native distribution of Acmispon tomentosus, 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
California CAL NORTHERN AMERICA
Mexico Northwest MXN

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 168 in flower of 195 examined

Proportion of examined Acmispon tomentosus in flower, by month
Month In flower Examined Share 95% interval
Jan 3 6 50% 19% to 81%
Feb 1 6 17% 3% to 56%
Mar 22 30 73% 56% to 86%
Apr 23 24 96% 80% to 99%
May 33 35 94% 81% to 98%
Jun 33 35 94% 81% to 98%
Jul 15 16 94% 72% to 99%
Aug 8 8 100% 68% to 100%
Sep 13 14 93% 69% to 99%
Oct 10 10 100% 72% to 100%
Nov 6 7 86% 49% to 97%
Dec 1 4 too few examined

Peak flowering in Aug. Each bar is the share of Acmispon tomentosus 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. 168 of 195 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. One month has fewer than 5 examined observations, so no proportion is drawn for it. 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 430 observations

Condition 5th percentile Median 95th percentile
Coldest month, mean daily low -1.1 °C 7.3 °C 9.9 °C
Warmest month, mean daily high 18.2 °C 27.1 °C 35.7 °C
Annual rainfall 294 mm 458 mm 983 mm
Rainfall in the driest quarter 4 mm 7 mm 25 mm

It is found where winters bring light frost. This is not care advice and it is not a forecast. It is a measurement: we sampled the climate at every one of the 430 research-grade observations of Acmispon tomentosus 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 18 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.

  • Acmispon heermannii (Durand & Hilg.) Brouillet
  • Acmispon heermannii var. orbicularis (A.Gray) Brouillet
  • Drepanolobus lanatus Nutt.
  • Drepanolobus lanatus Nutt. ex Torr. & A.Gray
  • Hosackia decumbens var. glabriuscula Hook. & Arn.
  • Hosackia heermannii Durand & Hilg.
  • Hosackia heermannii var. orbicularis A.Gray
  • Hosackia tomentosa Hook. & Arn.
  • Hosackia tomentosa subsp. glabriuscula (Hook. & Arn.) Abrams
  • Lotus eriophorus Greene
  • Lotus eriophorus var. heermannii Ottley
  • Lotus heermannii Greene
  • Lotus heermannii var. eriophorus (Greene) Ottley
  • Lotus heermannii var. orbicularis (A.Gray) Isely
  • Lotus tomentosus (Hook. & Arn.) Greene
  • Syrmatium eriophorum (Greene) A.Heller
  • Syrmatium heermannii (Durand & Hilg.) Greene
  • Syrmatium tomentosum (Hook. & Arn.) Vogel

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 LOHE. 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.