Taxon Report

Iris thompsonii R.C. Foster

Thompson's iris

Print Report

Taxon Summary

Iris thompsonii, commonly known as Thompson's iris, is a perennial rhizomatous herb in the Iridaceae that is found in California and elsewhere. It occurs within Lower montane coniferous forest, and North Coast coniferous forest, growing at elevations from 90 to 600 meters. Iris thompsonii is ranked 4.3, Plants of Limited Distribution, A Watch List; Not very threatened in California.

Classification


Scientific Name:	Iris thompsonii R.C. Foster
Common Name:	Thompson's iris
Family:	Iridaceae
Element Code:	PMIRI09120
USDA Plants Symbol:
Synonyms/Other Names:

Ecology and Life History


Lifeform:	perennial rhizomatous herb
Blooming Period: (Mar-Apr)May-Jun(Jul-Aug)	(Mar-Apr)May-Jun(Jul-Aug)
Elevation:	90-600 (295-1970)
General Habitats:	Lower montane coniferous forest, North Coast coniferous forest
Microhabitat:	Edges (often), Mesic (usually), Openings, Roadsides (sometimes), Serpentine (often), Streambanks (sometimes)
Microhabitat Details:

Conservation Status


CA Rare Plant Rank:	4.3
Global Rank:	G3
State Rank:	S3
State List:	None
Fed List:	None
Other Status:
CRPR Changes:	added to 4.3 on 2018-07-24

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: False
California Counties and Islands: Name (Code)
Del Norte (DNT), Siskiyou (SIS)
Quads: Name (Quad Code)
Broken Rib Mtn. (4112386), Cant Hook Mtn. (4112368), Gasquet (4112378), Happy Camp (4112374), Hiouchi (4112471), Hurdygurdy Butte (4112377), Klamath Glen (4112358), Shelly Creek Ridge (4112387)

Threat List Data from the CNDDB


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

Notes




Threats:

Taxonomy:
Considered to be a hybrid of I. douglasiana and I. innominata in OR.

Selected References

Proposed Addition to California Rare Plant Rank 4.3, G3 / S3 (2018)

Rhodora 38(450):199-201 (1936)

Madroño 37(2):113-123 (1990)

Iris thompsonii profile for potential Species of Conservation Concern evaluation (2018)

Aliso 4:1-72 (1958) [Hybrid Taxonomic Treatment]

Journal of Botany 83(12):1623-1629 (1996) [Hybrid Taxonomic Treatment]

Citation California Native Plant Society, Rare Plant Program. 2025. Rare Plant Inventory (online edition, v9.5.1). Website https://www.rareplants.cnps.org [accessed 29 October 2025].