Flora of North America species comparison

The green links below add additional plants to the comparison table. Blue links lead to other Web sites.
enable glossary links

Cirsium clavatum var. americanum
Photo is of parent taxon

Rocky Mountain fringe thistle
Involucres

ovoid to campanulate, 1.5–3 × 1.5–3 cm, glabrous or thinly arachnoid-tomentose with fine, non-septate trichomes.
Phyllaries

in 5–6 series, strongly imbricate to subequal, green or with maroon to dark brown subapical patch or appendage, linear to ovate, abaxial faces with narrow glutinous ridge;

outer and middle bases appressed, apical appendages erect or ascending, linear-lanceolate to obovate, entire or more commonly dilated, scarious, and erose-toothed to fringed, acicular-acuminate to broadly obtuse, spines erect or ascending, 1–6 mm, often flattened;

apices of inner sometimes flexuous or reflexed, narrow, flat, and entire or more commonly ± expanded, scarious, and lacerate-dentate.
Abaxial

leaf faces ± tomentose.
2n

= 34, 36 (as C. centaureae).

Cirsium clavatum var. americanum
Phenology Flowering summer (Jun–Sep).
Habitat Oak scrub, sagebrush scrub, grasslands, juniper-pine woodlands, aspen groves, openings in montane coniferous forests
Elevation 2100–3100 m (6900–10200 ft)
Distribution
from FNA
CO; UT; WY
[BONAP county map]
Discussion

Variety americanum is scattered in the Rocky Mountains of south-central Wyoming and Colorado. The varietal epithet americanum was based upon syntypes from both Colorado and California. The latter are referable to Cirsium remotifolium.

Variations in leaf characteristics, head size, and phyllary features combined with a narrow species concept led Osterhout and Rydberg to propose several species and hybrids for what I am treating as one taxon. Variety americanum certainly is polymorphic and in need of further study focused on local and regional variation. It is possible that some of the local variants in Colorado may deserve taxonomic recognition, but I have been unable to detect consistent patterns in the variation. Some specimens from Route and Jackson counties there closely approach var. clavatum. Others from southeastern Wyoming approach Cirsium pulcherrimum var. pulcherrimum and may be hybrids or derivatives of past hybridization.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 19, p. 128.
Parent taxa Asteraceae > tribe Cardueae > Cirsium > Cirsium clavatum
Sibling taxa
C. clavatum var. clavatum, C. clavatum var. osterhoutii
Synonyms Cnicus carlinoides var. americanus, C. centaureae, C. griseum, C. laterifolium, C. modestum, C. scapanolepis, C. spathulifolium
Name authority (A. Gray) D. J. Keil: Sida 21: 211. (2004)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



Type/paste one or more Latin names into the boxes above; matching taxa will show up below the box as you type. You can use the up/down arrow keys to move through the list.

(If the plant you're looking for doesn't show up in the auto-complete list, that means it either isn't described in Flora of North America yet, or it's listed under a synonym. And please note that Flora of North America is still missing several plant families, including Apiaceae, Boraginaceae, and Polemoniaceae.)

Choose a data source: Flora of North America

The species comparison tool is brought to you by:
Northwest Wildflowers