Cirsium altissimum
Cirsium inamoenum
roadside thistle, tall thistle
Davis' thistle, Greene's thistle, intermountain thistle, Jackson hole thistle
single, erect, villous with septate trichomes, sometimes ± glabrate, sometimes distally thinly tomentose;
branches few–many, ascending.
1–several, erect, thinly to densely gray-tomentose with fine, non-septate trichomes;
branches 0–many, ascending.
blades oblanceolate to elliptic or ovate, 10–40 × 1–13 cm, margins flat, finely spiny-toothed and otherwise undivided to coarsely toothed or shallowly pinnatifid, lobes broadly triangular, main spines 1–5 mm, abaxial faces white-tomentose, adaxial faces green, glabrate to villous with septate trichomes;
basal usually absent at flowering, winged-petiolate, bases tapered;
principal cauline well distributed, gradually reduced, bases narrowed, sometimes weakly clasping;
distal cauline well developed.
blades oblanceolate or elliptic, 10–35 × 1–7 cm, unlobed and spinulose to dentate or deeply pinnatifid, usually 5–8 pairs of lobes, well separated, linear to lance-triangular, spinulose to few toothed or lobed, main spines 2–7 mm, abaxial faces densely gray-tomentose or sometimes ± glabrate, adaxial gray to ± green, thinly tomentose or ± glabrate;
basal sometimes present at flowering, narrowly winged-petiolate;
principal cauline well distributed, gradually reduced, sometimes spinier than basal;
proximal winged-petiolate, mid sessile, bases spiny-winged, decurrent 1–3 cm;
distal becoming bractlike, often unlobed or less deeply divided than proximal.
0–5 cm (leafy-bracted).
0–25 cm.
ovoid to broadly cylindric or campanulate, (2–)2.5–3.5(–4) × (1.5–)2–3(–4) cm, thinly arachnoid.
ovoid or hemispheric to campanulate, 2–3 × 1.5–5 cm, glabrous or loosely floccose to densely arachnoid.
tips 4–6 mm.
pink to purple (white), 20–35 mm, tubes 10–16 mm, throats 5–12 mm, lobes 5–9 mm.
dull white or faintly lavender-tinged to bright pink-purple, 19–31 mm, tubes 7–13 mm, throats 6.5–9.5 mm, lobes 4–8 mm;
style tips 3.5–7 mm.
in 10–20 series, strongly imbricate, greenish with subapical darker central zone, ovate (outer) to lanceolate (inner), abaxial faces with a narrow glutinous ridge (milky when fresh, dark when dry), outer and middle entire, bodies appressed, spines slender, abruptly spreading, 3–4 mm;
apices of inner phyllaries spreading, narrow, flattened, entire, spines spreading, slender, 3–4 mm;
apices of inner phyllaries spreading, narrow, flattened, ± dilated, ± erose or finely serrulate.
in 6–10 series, strongly imbricate or sometimes subequal, greenish to brown, ovate to linear-lanceolate (outer) to linear (inner), entire, abaxial faces with narrow or scarcely developed glutinous ridge;
outer and mid appressed or apices ascending to spreading, linear, bodies entire, spines ascending to abruptly spreading, usually fine, 2–6 mm;
apices of inner narrow, spine-tipped or spineless.
1–many, in corymbiform or paniculiform arrays, (± elevated above principal cauline leaves), not subtended by ring of spiny bracts.
1–many, in open corymbiform arrays or crowded near stem tips.
tan to dark brown, 4–5.5 mm, apical collars stramineous, 0.5–1 mm;
pappi 12–24 mm.
brown, 5–8 mm, apical collars not differentiated;
pappi 12–25 mm.
= 18.
= 32, 34, 36.
Cirsium altissimum
Cirsium inamoenum
Plants of Cirsium altissimum ranging from southern Minnesota to Texas often have more deeply divided leaves than do populations in other portions of the species’ range. Some botanists (e.g., R. J. Moore and C. Frankton 1969; D. S. Correll and M. C. Johnston 1970) have treated those plants as C. iowense. Others (e.g., R. E. Brooks 1986; H. A. Gleason and A. Cronquist 1991; G. B. Ownbey and T. Morley 1991) have treated them as C. altissimum. Still others considered them to be derivatives of hybridization between C. altissimum and C. discolor (J. T. Kartesz and C. A. Meacham 1999) and treated them as C. ×iowense. Indeed the existence of these plants blurs the distinction between C. altissimum and C. discolor, and herbarium specimens are often difficult to assign.
Natural hybrids between Cirsium altissimum and C. discolor are well documented (R. A. Davidson 1963; G. B. Ownbey and Hsi Y.-T. 1963; Ownbey 1964; S. Dabydeen 1997). Ownbey and Dabydeen both reported that apparent F1 hybrids between the two species have low seed set in comparison with the parental taxa. W. L. Bloom (1977) reported that the chromosomes of the two species differ by several rearareaments. Dabydeen reported a count of 2n = 19 with multiple meiotic irregularities for an apparent F1 hybrid. However, the presence of numerous individuals and populations seemingly intermediate between C. altissimum and C. discolor indicates that although F1 hybrids have low fertility, long-term processes may have stabilized hybrid derivatives of higher fertility. Ownbey and Hsi reported mitotic counts of 2n = 18 and 20 from a population that they treated as C. altissimum. In their discussion they noted that their plants represented “the segregate called C. iowense” and had been collected a short distance from that taxon’s type locality. R. J. Moore and C. Frankton (1969) reported a chromosome number of 2n = 18 for a plant from Texas that they considered to be C. iowense. Further investigation of morphologic variation, chromosome number, meiotic behavior, and fertility is needed of populations named as C. iowense to determine how those plants should be treated.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Varieties 2 (2 in the flora).
Cirsium inamoenum is a variable complex across the northern Great Basin and adjacent mountains. A. Cronquist (1994) treated this complex as a single species under the name C. subniveum without infraspecific taxa and including taxa that formerly had been assigned to C. utahense (e.g., J. T. Howell 1960b). Some populations consist of small-headed, white-flowered plants with strong involucres and short, appressed phyllaries. Others have larger heads, white or lavender to pink-purple corollas, and phyllaries with longer, ascending to spreading tips. My treatment of this complex as C. inamoenum is similarly inclusive as was Cronquist’s treatment of C. subniveum, except that I believe C. humboldtense, which Cronquist included, is probably a derivative of hybridization between C. subniveum and C. eatonii var. peckii. I have observed such hybrids on the slopes of Steens Mountain in Harney County, Oregon, and the type of C. humboldtense closely resembles some of the introgressants. I have examined several other specimens that are likely the products of hybridization of C. inamoenum with other varieties of C. eatonii.
I have chosen to recognize racial differentiation within Cirsium inamoenum at the rank of variety. The main difference between Cirsium inamoenum var. inamoenum and var. davisii is corolla color. Unfortunately this feature is sometimes difficult to determine on herbarium specimens, and many collectors fail to include corolla color on specimen labels. Some geographic overlap occurs between var. davisii, which has a distribution centered in northeastern Utah, southeastern Idaho, and adjacent southwestern Wyoming, and the more widespread var. inamoenum.
Plants of northeastern Oregon, southeastern Washington, and adjacent western Idaho often have large heads and densely tomentose foliage. These were named Cirsium wallowense by Peck. Similar plants occur sporadically in other portions of the range of Cirsium inamoenum var. inamoenum and I chose not to recognize these northwestern populations as a third variety. Additional study might clarify the relationships of these plants.
Some specimens of Cirsium inamoenum in central Nevada and Utah approach C. neomexicanum. It seems likely that these species have interacted in the past.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Corollas white or pale lavender | var. inamoenum |
1. Corollas lavender to rich pink-purple | var. davisii |
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