Cirsium clavatum var. americanum

(A. Gray) D. J. Keil

Sida 21: 211. 2004.

Common names: Rocky Mountain fringed thistle
Endemic
Basionym: Cnicus carlinoides var. americanus A. Gray Proc. Amer. Acad. Arts 10: 48. 1874
Synonyms: Cirsium centaureae (Rydberg) K. Schumann Cirsium griseum (Rydberg) K. Schumann Cirsium laterifolium (Osterhout) Petrak Cirsium modestum (Osterhout) Cockerell Cirsium scapanolepis Petrak Cirsium spathulifolium Rydberg
Treatment appears in FNA Volume 19. Treatment on page 128. Mentioned on page 126, 127.

Abaxial leaf faces ± tomentose. 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. 2n = 34, 36 (as C. centaureae).


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

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.

Selected References

None.

Lower Taxa

None.

"fine" is not a number.

green +  and gray +
villous +, glabrate +, glabrous or +  and thinly densely arachnoid-tomentose +
short-tailed +
spineless +  and twisted +
dentate +, entire +  and spine-tipped +
erect +  and spreading +
innermost +
scarious +
ascending +  and erect +
erose-toothed +  and fringed acicular-acuminate +
racemiform +, paniculiform +  and corymbiform +
indeterminate +  and determinate +
David J. Keil +
(A. Gray) D. J. Keil +
petiolate +  and sessile +
lacerate-dentate +  and entire +
decurrent +
Cnicus carlinoides var. americanus +
compound +  and simple +
5 cm50 mm <br />0.05 m <br /> (40 cm400 mm <br />0.4 m <br />) +
pinnatifid;unlobed;oblong;oblanceolate or elliptic +
3cm;11cm +
10-nerved or 20-nerved +  and rugose +
ascending;arising +
slender +
tawny +  and white +
? (?) +  and ? (?) +
Rocky Mountain fringed thistle +
actinomorphic +
creamy white +  and pale pinkish +
1.6 cm16 mm <br />0.016 m <br /> (2 cm20 mm <br />0.02 m <br />) +
tan +  and dark-brown +
compressed +  and ovoid +
fertile +  and bisexual +
Colo. +, Utah +  and Wyo. +
2100–3100 m +
gray-canescent +  and glabrous +
lacerate-dentate +  and entire +
pistillate +, staminate +  and neuter +
winged +  and beaked +
dispersed +
Oak scrub, sagebrush scrub, grasslands, juniper-pine woodlands, aspen groves, openings in montane coniferous forests +
clustered +  and or +
indeterminate +
each +  and sessile +
1.5 cm15 mm <br />0.015 m <br /> (3 cm30 mm <br />0.03 m <br />) +
arachnoid-tomentose +  and glabrous +
ovoid;campanulate +
1.5 cm15 mm <br />0.015 m <br /> (3 cm30 mm <br />0.03 m <br />) +
sessile +  and petiolate +
cauline +  and basal +
bristle-tipped +
ascending-spreading;retrorse +
linear +  and triangular-ovate +
slender +
0.5 cm5 mm <br />0.005 m <br /> (0.7 cm7 mm <br />0.007 m <br />) +
few-lobed +  and dentate +
0.2 cm2 mm <br />0.002 m <br /> (0.5 cm5 mm <br />0.005 m <br />) +
entire +  and dentate +
usually lobed +  and dissected +
with maroon to dark-brown subapical patch or appendage +  and green +
linear +  and ovate +
2-carpellate +
persistent +
1.4 cm14 mm <br />0.014 m <br /> (1.6 cm16 mm <br />0.016 m <br />) +
0 cm0 mm <br />0 m <br /> (30 cm300 mm <br />0.3 m <br />) +
Flowering summer (Jun–Sep). +
middle +  and outer +
papillate +  and smooth +
bearing subulate enations +, hairy +  and bristly +
flat;convex +
glutinous +
tawny;white +
setiform +  and plumose +
exalbuminous +
subequal +
ascending +  and erect +
flattened +
0.1 cm1 mm <br />0.001 m <br /> (0.6 cm6 mm <br />0.006 m <br />) +
spiny-winged +, simple +  and branched +
ascending +  and erect +
1 +  and several +
appendaged +  and truncate +
dilated +  and swollen +
enlarged +
0.35 cm3.5 mm <br />0.0035 m <br /> (0.5 cm5 mm <br />0.005 m <br />) +
maroon +  and dark-brown +
Cirsium centaureae +, Cirsium griseum +, Cirsium laterifolium +, Cirsium modestum +, Cirsium scapanolepis +  and Cirsium spathulifolium +
Cirsium clavatum var. americanum +
Cirsium clavatum +
variety +
cylindric +
expanded +
0.4 cm4 mm <br />0.004 m <br /> (0.75 cm7.5 mm <br />0.0075 m <br />) +
bristly-dentate to coarsely +
slender +
0.65 cm6.5 mm <br />0.0065 m <br /> (0.9 cm9 mm <br />0.009 m <br />) +
perennial +  and biennial +
polycarpic +  and monocarpic +
20 cm200 mm <br />0.2 m <br /> (100 cm1,000 mm <br />1 m <br />) +
tree +, vine +, shrub +  and subshrub +
1 cm10 mm <br />0.01 m <br /> (3 cm30 mm <br />0.03 m <br />) +