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Osterhout's thistle

Fish Lake thistle, fringe thistle

Habit Biennials or monocarpic or polycarpic perennials, 20–100 cm; taproots sometimes with branched caudices.
Stems

1–several, erect or ascending, glabrous or thinly arachnoid-tomentose;

branches 0–10+, slender, usually arising in distal 1/2, ascending.

Leaves

blades oblong to oblanceolate or elliptic, 5–40 × 3–11 cm, unlobed and merely spinulose-dentate or more commonly regularly deeply pinnatifid, lobes well separated to crowded, linear to triangular-ovate, ascending-spreading to retrorse, merely spinulose to coarsely dentate or proximally few-lobed, main spines 2–5(–7) mm, slender, abaxial faces green to gray, glabrous or thinly to densely arachnoid-tomentose, sometimes glabrate, often villous with septate trichomes along veins, adaxial green, glabrous;

basal usually present at flowering, sessile or petiolate;

principal cauline well distributed, proximal usually winged-petiolate, mid sessile, decurrent as spiny wings 1–3 cm;

distal cauline ± reduced.

Peduncles

0–30 cm.

Involucres

ovoid to campanulate, 2–2.8 × 1.5–3 cm, villous-ciliate with long septate trichomes connecting adjacent phyllaries and/or thinly arachnoid-tomentose.

ovoid to campanulate, 1.5–3 × 1–3 cm, glabrous to thinly arachnoid-tomentose and/or villous-ciliate, with long septate trichomes connecting adjacent phyllaries.

Corollas

creamy white to pale pinkish, 16–20 mm, tubes 6.5–9 mm, throats 4–7.5 mm, lobes 4–6 mm;

style tips 3.5–5 mm.

Phyllaries

in 5–6 series, imbricate or subequal, green or with maroon to dark brown subapical patch or appendage, linear to linear-lanceolate, abaxial faces with narrow glutinous ridge that is often concealed by trichomes;

outer and middle bases appressed, apical appendages erect or stiffly ascending, linear-lanceolate to acicular, entire or spinulose-dentate, spines erect or ascending, 2–5 mm;

apices of inner sometimes flexuous or reflexed, narrow, flat, and entire or expanded, scarious, and lacerate-dentate.

in 5–6 series, imbricate or subequal, outer green or with maroon to dark brown subapical patch or appendage, linear to ovate, abaxial faces with narrow glutinous ridge that may be concealed by trichomes;

outer and middle with bases appressed, apical appendages erect or ascending, ovate to linear-lanceolate or acicular, entire or spinulose to broadly expanded, scarious, and erose-dentate, apical appendages, spines erect or ascending, 1–5 mm, ± flattened;

apices of inner sometimes flexuous or reflexed, narrow, flat, entire or ± expanded, scarious and lacerate-dentate.

Heads

few–many, borne singly or clustered in corymbiform, paniculiform, or racemiform arrays at tips of main stem and branches, sometimes also in distal axils not closely subtended by clustered leafy bracts.

Cypselae

tan to dark brown, 5–6 mm, apical collars not or scarcely differentiated;

pappi 14–16 mm.

Abaxial

leaf faces ± tomentose.

Cirsium clavatum var. osterhoutii

Cirsium clavatum

Phenology Flowering summer (Jul–Aug).
Habitat Openings in montane coniferous forests, subalpine, alpine
Elevation 3000–3600 m (9800–11800 ft)
Distribution
from FNA
CO
[BONAP county map]
from FNA
CO; UT; WY; Central Rocky Mountains
[WildflowerSearch map]
[BONAP county map]
Discussion

The densely pubescent involucre of var. osterhoutii is a feature that links those plants with Cirsium eatonii var. eriocephalum. Some specimens tentatively assigned to C. clavatum var. osterhoutiii may be derivatives of past introgression with C. eatonii var. eriocephalum. Congested heads and strongly undulate leaves with numerous closely spaced lobes are features that suggest such a relationship. Further studies at both population and regional levels are needed to establish the nature of the variation patterns. Where I have observed var. osterhoutii in the field, populations appeared to be morpologically stable, and there was no evidence of current introgression with C. eatonii.

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

Varieties 3 (3 in the flora).

Cirsium clavatum is a polymorphic and variable species.

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

Key
1. Involucres densely villous or tomentose with long, septate trichomes connecting adjacent phyllaries
var. osterhoutii
1. Involucres glabrous or thinly arachnoid-tomentose with fine, non-septate trichomes
→ 2
2. Some or all of the phyllaries usually with dilated, scarious, erose to fringed appendages; mostly Colorado and Wyoming
var. americanum
2. Phyllaries usually entire; w Colorado and Utah
var. clavatum
Source FNA vol. 19, p. 128. FNA vol. 19, p. 126.
Parent taxa Asteraceae > tribe Cardueae > Cirsium > Cirsium clavatum Asteraceae > tribe Cardueae > Cirsium
Sibling taxa
C. clavatum var. americanum, C. clavatum var. clavatum
C. altissimum, C. andersonii, C. andrewsii, C. arizonicum, C. arvense, C. barnebyi, C. brevifolium, C. brevistylum, C. canescens, C. carolinianum, C. ciliolatum, C. crassicaule, C. cymosum, C. discolor, C. douglasii, C. drummondii, C. eatonii, 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. clavatum var. americanum, C. clavatum var. clavatum, C. clavatum var. osterhoutii
Synonyms Carduus osterhoutii, C. osterhoutii, C. araneans Cnicus clavatus
Name authority (Rydberg) D. J. Keil: Sida 21: 212. (2004) (M. E. Jones) Petrak: Beih. Bot. Centralbl. 35(2): 310. (1917)
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