Taxon Report

Eriogonum argillosum J.T. Howell

clay buckwheat

Print Report

Taxon Summary

Eriogonum argillosum, commonly known as clay buckwheat, is a annual herb in the Polygonaceae that is found only in California. It occurs within Cismontane woodland, and Valley and foothill grassland, growing at elevations from 75 to 930 meters. Eriogonum argillosum is ranked 1B.2, Plants Rare, Threatened or Endangered in California and Elsewhere; Moderately threatened in California.

Classification


Scientific Name:	Eriogonum argillosum J.T. Howell
Common Name:	clay buckwheat
Family:	Polygonaceae
Element Code:	PDPGN080J0
USDA Plants Symbol:	ERAR9
Synonyms/Other Names:

Ecology and Life History


Lifeform:	annual herb
Blooming Period: Mar-Jun	Mar-Jun
Elevation:	75-930 (245-3050)
General Habitats:	Cismontane woodland, Valley and foothill grassland
Microhabitat:	Clay (usually)
Microhabitat Details:	Clay endemic, found in areas where competition with non-native plants is reduced, such as landslides (clayslides). Sometimes on sandy clays.

Conservation Status


CA Rare Plant Rank:	1B.2
Global Rank:	G3G4
State Rank:	S3S4
State List:	None
Fed List:	None
Other Status:
CRPR Changes:	changed from 4.3 to 1B.2 on 2026-06-12

Occurrence Data from the CNDDB


Total Occurrences:	0
Element Occurrence Ranks:
Excellent (A)	0
Good (B)	0
Fair (C)	0
Poor (D)	0
None (X)	0
Unknown (U)	0

Location


California Endemic: True
California Counties and Islands: Name (Code)

Quads: Name (Quad Code)

Threat List Data from the CNDDB


Threat List Total:	0
EOs with Threat Listed:	Total EOs	% of EOs
	0	0 %

Notes



Serpentine previously included in general habitat based on one specimen record from SCL Co. collected "on a clay slope that is related to serpentine" (Clifton 23190, DAV); now considered extirpated from SCL Co. and no other occurrences have been documented on serpentine or serpentine-derived soils.
Threats:
Threatened by development, urbanization, agriculture, and competition from non-native plants.
Taxonomy:
Sometimes confused with E. angulosum (which has an un-ribbed, hairy involucre and glandular hairy perianth vs a ribbed, glabrous involucre and glabrous perianth in E. argillosum) and E. ordii (which has a densely hairy perianth vs a glabrous perianth in E. argillosum).

Selected References

Proposed change from CRPR 4.2 to 1B.2, G2G3 / S2S3 (2026)

Leaflets of Western Botany 1: 11-14 (1932)

Phytologia 66(4): 376 (1989)

Citation California Native Plant Society, Rare Plant Program. 2026. Rare Plant Inventory (online edition, v9.5.1). Website https://www.rareplants.cnps.org [accessed 19 June 2026].