Cirsium clavatum var. clavatum
Cirsium clavatum var. americanum
Fish Lake thistle
Rocky Mountain fringe thistle
ovoid to campanulate, 1.5–2 × 1–2 cm, glabrous or thinly arachnoid-tomentose with fine, non-septate trichomes.
ovoid to campanulate, 1.5–3 × 1.5–3 cm, glabrous or thinly arachnoid-tomentose with fine, non-septate trichomes.
in 5–6 series, strongly imbricate, green or with dark subapical patch, lanceolate to ovate, abaxial faces with narrow glutinous ridge;
outer and middle bases appressed, apical appendages erect or ascending, linear-lanceolate, entire, usually not scarious or fringed, acicular-acuminate, spines erect or ascending, 3–6 mm;
apices of inner sometimes flexuous or reflexed, narrow, flat, and entire or minutely toothed to slightly expanded and erose.
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.
leaf faces glabrous to ± tomentose.
leaf faces ± tomentose.
= 34, 36 (as C. centaureae).
Cirsium clavatum var. clavatum
Cirsium clavatum var. americanum
Cirsium clavatum grows from the Colorado Plateau of central Utah eastward into the Rocky Mountains of western Colorado. R. J. Moore and C. Frankton (1965) suggested that C. clavatum (i.e., var. clavatum here) is a derivative of hybridization between C. eatonii and C. centaureae (i.e., C. clavatum var. americanum here). S. L. Welsh (1983) noted that the distribution of var. clavatum is distinct from those of var. americanum and C. eatonii. It is certainly possible that ancient hybridization may have contributed to the origin of var. clavatum, but there is no indication that the modern plants over most of its range are hybrids. The morphology of certain plants from southeastern Utah indicates a possibility of hybridization between C. clavatum and C. eatonii var. eatonii. The close relationship between var. clavatum and var. americanum is evident in the many overlapping vegetative features. The recently described C. clavatum var. markaguntense S. L. Welsh is a minor variant with subentire glabrous leaves.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.)
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