Cirsium foliosum
Cirsium canescens
elk thistle, Evert's thistle, foliose thistle, leafy or foliose or elk thistle, leafy thistle
Platte thistle, prairie thistle
usually 1, erect, stout, ± fleshy, simple, very leafy, densely villous or tomentose with septate trichomes.
usually 1, erect, ± densely gray-tomentose with fine, non-septate trichomes;
branches 0 or few, usually above middle in distal 1/2, ascending.
blades linear-oblong to oblanceolate (elliptic), 5–20(–25) × 1–4(–7) cm, subentire to dentate or pinnatifid, lobes lance-oblong to triangular, spinulose to spiny-dentate or shallowly lobed, main spines slender, 2–5(–10) mm, abaxial faces often thinly gray- or white-tomentose with felted arachnoid trichomes, ± villous along major veins with septate trichomes, adaxial green, glabrous to thinly arachnoid, often ± villous with septate trichomes;
basal usually present at flowering, spiny winged-petiolate or sessile;
principal cauline well distributed, proximally winged-petiolate, distally sessile, not or only slightly reduced;
distal often narrower than proximal.
blades oblong to elliptic or obovate, 10–25(–40) × 2–6(–12) cm, coarsely dentate or shallowly lobed to deeply pinnatifid, lobes well separated, triangular to linear or oblong, often revolute-margined, ascending to spreading, spinulose to spinose-dentate, main spines 2–3(–10) mm, faces gray-tomentose, more densely abaxially, sometimes glabrate adaxially;
basal usually present at flowering, winged-petiolate;
principal cauline progressively reduced distally, bases decurrent as spiny wings 1–5 cm, sometimes with expanded auricles;
distal cauline usually much reduced, less lobed.
0–1 cm.
0–10 cm.
broadly ovoid, 2–2.5 × 1.5–2 cm, green, glabrous to densely villous with septate trichomes on margins.
hemispheric to broadly campanulate, usually truncate or indented at base, 3–4 × 2.5–4 cm in first-formed heads, often smaller (1.5–2 cm) in later ones, loosely arachnoid on phyllary margins or glabrate.
white to pale pink, 21–25 mm, tubes 12–14 mm, throats (very slender, scarcely larger than tubes) 6–7 mm, lobes 3–4 mm;
style tips 2.5–3 mm, short exserted.
dull white or lavender-tinged, 20–35 mm, tubes 10–17 mm, throats 6–11 mm, lobes 4–9 mm;
style tips 5–8 mm.
in 4–6 series, imbricate, lanceolate or ovate (outer) to linear-lanceolate (inner), bases appressed, margins of outer entire, abaxial faces without glutinous ridge, apices appressed to ascending, spines straight, slender, 2–3 mm;
apices of inner erect, straight.
in 6–9 series, imbricate, ovate-lanceolate (outer) to linear-lanceolate (inner), abaxial faces with prominent glutinous ridge;
bodies of outer and middle appressed, acute, spines ascending to spreading, 2–4(–8) mm;
apices of inner expanded and flat, often twisted, scabrid-margined, and erose, spineless.
few–many, erect, sessile or subsessile, crowded in dense, woolly, leafy-bracted, subcapitate arrays, closely subtended and overtopped by crowded leafy bracts.
1–10+, terminal on branches or in distal axils, in openly corymbiform to racemiform arrays.
light brown, 4–5.5 mm, apical collars yellow, narrow;
pappi 23–29 mm, exceeding corollas.
light brown, 5–7 mm, sometimes with darker streaks, apical collar very narrow, lighter colored;
pappi 18–30 mm, usually noticeably shorter than corolla.
= 34.
= 34, 36.
Cirsium foliosum
Cirsium canescens
Cirsium foliosum occurs in the northern Rockies from Wyoming to the Yukon and eastward to the Slave River area in the Northwest Territories and northeastern Alberta. Reports for Alaska are unconfirmed (R. Lipkin, Alaska Natural Heritage Program, pers. comm.). The name Cirsium foliosum has been misapplied to a wide range of plants across the western United States that now are treated as one or another variety of the polymorphic C. scariosum. The only documented occurrences of C. foliosum in the lower 48 states are in the mountains of northern Wyoming. Somewhat similar plants from other mountain areas of the western United States are treated as C. scariosum var. scariosum. During Pleistocene glaciations the ancestors of C. foliosum undoubtedly occupied a more southerly distribution and very likely came into direct contact with ancestral populations of C. scariosum. The observed similarities between C. foliosum and C. scariosum var. scariosum may be a relic of hybridization in that ancient contact zone. On the other hand, the corolla features of C. foliosum suggest that this is a self-pollinating species, perhaps derived from an ancestral population similar to the modern C. scariosum var. scariosum.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Cirsium canescens grows in the northern Great Plains from eastern Montana and Wyoming to eastern Colorado and Nebraska; an upland race occurs in the Rocky Mountains of eastern Colorado. It has been reported from Iowa, North Dakota, and Ohio; I have not seen specimens from those states. It is adventive in northeastern California.
Cirsium canescens hybridizes locally with C. scariosum and C. parryi. Further investigations may reveal that high-elevation forms of C. canescens from the mountains of Colorado are worthy of taxonomic recognition. These plants flower later than the low elevation forms of the Great Plains and occur in rather different ecologic conditions, but I have found no features that readily distinguish them. Populations of C. canescens have been particularly affected by the seedhead weevil Rhinocyllus conicus, introduced to North America to control weedy species of Carduus (S. M. Louda et al. 1997; Louda 1998).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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OR
Flora NW
PNW Herbaria
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USDA Plants Database
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