Flora of North America species comparison

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Cirsium engelmannii

Cirsium eatonii

blackland thistle, Engelmann's thistle

Eaton's thistle, mountaintop thistle, Peck's thistle, Steens Mountain thistle
Habit Biennials or monocarpic perennials, 40–200 cm; taproots and clusters of coarse fibrous roots that often have tuberlike thickenings. Perennials, 10–150 cm; taprooted caudices.
Stems

single, erect, often branched above middle, thinly arachnoid-tomentose, ± glabrate;

branches few, ascending.

1–several, (fleshy), erect or ascending, simple to sparingly branched in distal 1/2, sometimes openly branched, glabrous to villous or tomentose with septate trichomes, sometimes ± glabrate;

branches on distal stems 0–many, ascending.
Leaves

blades elliptic or ovate, 5–20 × 1–10 cm, usually deeply pinnatifid, lobes narrowly to broadly triangular, sinuses broad, rounded (basal and distal cauline sometimes less divided, lobes linear-lanceolate), margins revolute, spreading, entire or spinulose to remotely few-toothed or sharply lobed, main spines slender, 1–5 mm, abaxial faces white-tomentose, adaxial green, villous with septate trichomes or glabrate;

basal usually absent at flowering, winged-petiolate, bases tapered;

principal cauline well distributed, gradually reduced, bases narrowed, sometimes weakly clasping;

distal reduced, widely separated, distalmost bractlike.

blades oblong, 10–30 × 1–5 cm, margins usually strongly undulate, unlobed and spiny-dentate or shallowly to deeply pinnatifid with 10–20 pairs of lobes, teeth or lobes closely spaced, often overlapping, lance-oblong to broadly triangular, deeply 3-lobed, ± spiny-dentate, main spines 2–12 mm, abaxial faces glabrous or villous with septate trichomes along midveins to densely arachnoid-tomentose, adaxial glabrous or villous with septate trichomes along midveins;

basal often present at flowering, spiny winged-petiolate or sessile;

principal cauline many, well distributed, proximally ± winged-petiolate, distally sessile, gradually reduced;

distal not much reduced, often closely subtending heads.
Peduncles

2–20+ cm, essentially naked with much reduced bracts.

0–14+ cm.
Involucres

ovoid to broadly cylindric or campanulate, 2.5–3.5 × 2–3 cm, thinly arachnoid.

green or suffused with dark purple, broadly ovoid to campanulate, 2–5 × 1.5–5 cm (appearing wider when pressed), loosely to densely villous or tomentose with septate trichomes and/or arachnoid-tomentose with finer, non-septate trichomes.
Corollas

pink to purple (white), 32–38 mm, tubes 15–20 mm, throats 6–9 mm, lobes 8–11 mm;

style tips 5–6 mm.

ochroleucous or yellow to lavender, pink, or purple, 15–35 mm, tubes 3.5–10 mm, throats 5–14 mm, lobes (linear), 4–12.5 mm;

style tips 3–6 mm, conspicuously exserted beyond corolla lobes.
Phyllaries

in 10–12 series, strongly imbricate, greenish with subapical darker central zone, ovate (outer) to lanceolate (inner), abaxial faces with narrow glutinous ridge;

outer and middle entire, bodies appressed, spines abruptly spreading to deflexed, slender, 2–4 mm;

apices of inner phyllaries narrow, flexuous, flattened, entire or finely erose.

in 4–5 series, subequal, bases short-appressed, abaxial faces without or with very narrow glutinous ridge, apices usually stiffly ascending to spreading, linear-acicular, tapering to spines 7–35 mm;

outer usually pinnately spiny, sometimes entire;

apices of inner straight, plane or spine-tipped.
Heads

1–10+, borne at tips of main stem and branches.

1–many, erect or nodding, closely subtended by spiny-fringed bracts, usually sessile or short-pedunculate and crowded in subcapitate, spiciform, or racemiform (less commonly in openly branched) arrays.
Cypselae

brown, 5–6 mm, apical collars yellow, ca. 1 mm;

pappi 25–30 mm.

dark brown, 5.5–7 mm, apical collars stramineous or not differentiated;

pappi 12–25 mm.
2n

= 18 (as C. terrae-nigrae), 20 + 1B.

Cirsium engelmannii

Cirsium eatonii
Phenology Flowering spring–summer (May–Jul).
Habitat Tallgrass prairies, old fields, roadsides, oak savannas, forest edges, in calcareous clay or rarely sandy soils
Elevation 50–200 m (200–700 ft)
Distribution
from FNA
LA; OK; TX
[BONAP county map]
from FNA
CO; ID; MT; NM; NV; OR; UT; WY; Rocky Mountains and high peaks of Great Basin desert region
[WildflowerSearch map]
[BONAP county map]
Discussion

Cirsium engelmannii occurs mostly in the blackland prairies of eastern Texas. It ranges northward into southeastern Oklahoma and eastward to northwestern Arkansas.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Varieties 7 (7 in the flora).

Cirsium eatonii is a polymorphic species widely distributed in a high elevation archipelago across the central Rocky Mountains and the Intermountain Region. During Pleistocene glacial episodes, the progenitors of this species complex undoubtedly occupied lower elevation sites and likely had more contiguous populations. Post-glacial isolation of these populations in allopatric high elevation sites has allowed them to differentiate to a greater or lesser extent. Prehistoric or recent introgressive hybridization with other thistle species probably has contributed to the diversification of the complex (R. J. Moore and C. Frankton 1965). Several of the races recognized here as varieties have been treated in the past as species (e.g., C. clokeyi, C. peckii). Their current geographic isolation and more or less distinctive features might support such recognition, but application of this approach across the complex would result in a proliferation of microspecies.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Involucres densely tomentose, individual phyllaries ± obscured by pubescence
→ 2
1. Involucres glabrous or thinly tomentose, individual phyllaries evident
→ 5
2. Arrays nodding; corollas yellow or pink to pale purple
var. eriocephalum
2. Arrays erect; corollas white or pink to deep purple
→ 3
3. Corolla throats 8–11.5 mm; se Oregon, nw Nevada
var. peckii
3. Corolla throats 3.5–8 mm
→ 4
4. Plants 50–150 cm, strictly erect; corollas pink or pale to deep purple; s Colorado
var. hesperium
4. Plants 10–65 cm, ascending to erect; corollas white to pink or lavender; Idaho and Montana to Utah and n Colorado
var. murdockii
5. Corollas usually 25–35 mm
→ 6
5. Corollas usually 17–25 mm
→ 7
6. Longest pappus bristles 16–18 mm
var. clokeyi
6. Longest pappus bristles 20–25 mm
var. viperinum
7. Most outer phyllaries with lateral spines; Nevada and Utah
var. eatonii
7. Most outer phyllaries without lateral spines; nw Nevada and se Oregon
var. peckii
Source FNA vol. 19, p. 117. FNA vol. 19.
Parent taxa Asteraceae > tribe Cardueae > Cirsium Asteraceae > tribe Cardueae > Cirsium
Sibling taxa
C. altissimum, C. andersonii, C. andrewsii, C. arizonicum, C. arvense, C. barnebyi, C. brevifolium, C. brevistylum, C. canescens, C. carolinianum, C. ciliolatum, C. clavatum, C. crassicaule, C. cymosum, C. discolor, C. douglasii, C. drummondii, C. eatonii, C. edule, C. flodmanii, C. foliosum, C. fontinale, C. grahamii, C. helenioides, C. hookerianum, C. horridulum, C. hydrophilum, C. inamoenum, C. joannae, C. kamtschaticum, C. lecontei, C. longistylum, C. mohavense, C. muticum, C. neomexicanum, C. nuttallii, C. occidentale, C. ochrocentrum, C. ownbeyi, C. palustre, C. parryi, C. perplexans, C. pitcheri, C. praeteriens, C. pulcherrimum, C. pumilum, C. quercetorum, C. remotifolium, C. repandum, C. rhothophilum, C. rydbergii, C. scariosum, C. texanum, C. tracyi, C. turneri, C. undulatum, C. vinaceum, C. virginianum, C. vulgare, C. wheeleri, C. wrightii
C. altissimum, C. andersonii, C. andrewsii, C. arizonicum, C. arvense, C. barnebyi, C. brevifolium, C. brevistylum, C. canescens, C. carolinianum, C. ciliolatum, C. clavatum, C. crassicaule, C. cymosum, C. discolor, C. douglasii, C. drummondii, C. edule, C. engelmannii, C. flodmanii, C. foliosum, C. fontinale, C. grahamii, C. helenioides, C. hookerianum, C. horridulum, C. hydrophilum, C. inamoenum, C. joannae, C. kamtschaticum, C. lecontei, C. longistylum, C. mohavense, C. muticum, C. neomexicanum, C. nuttallii, C. occidentale, C. ochrocentrum, C. ownbeyi, C. palustre, C. parryi, C. perplexans, C. pitcheri, C. praeteriens, C. pulcherrimum, C. pumilum, C. quercetorum, C. remotifolium, C. repandum, C. rhothophilum, C. rydbergii, C. scariosum, C. texanum, C. tracyi, C. turneri, C. undulatum, C. vinaceum, C. virginianum, C. vulgare, C. wheeleri, C. wrightii
Subordinate taxa
C. eatonii var. clokeyi, C. eatonii var. eatonii, C. eatonii var. eriocephalum, C. eatonii var. hesperium, C. eatonii var. murdockii, C. eatonii var. peckii, C. eatonii var. viperinum
Synonyms C. virginianum var. filipendulum, C. terrae-nigrae Cnicus eatonii
Name authority Rydberg: Fl. Rocky Mts., 1069. (1917) (A. Gray) B. L. Robinson: Rhodora 13: 240. (1911)
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).



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