Cirsium scariosum var. americanum

(A. Gray) D. J. Keil

Sida 21: 215. 2004.

Common names: Dinnerplate or sessile or stemless thistle
Illustrated
Basionym: Cirsium acaule var. americanum A. Gray Proc. Acad. Nat. Sci. Philadelphia 15: 68. 1864
Synonyms: Cirsium acaulescens (A. Gray) K. Schumann Cirsium americanum (A. Gray) K. Schumann Cirsium coloradense subsp. acaulescens (A. Gray) Petrak Cirsium coloradense subsp. longissimum (A. Heller) Petrak Cirsium drummondii var. acaulescens (A. Gray) J. F. Macbride Cirsium drummondii subsp. latisquamum Petrak Cirsium drummondii var. oregonense Petrak Cirsium drummondii subsp. vexans Petrak Cirsium tioganum
Treatment appears in FNA Volume 19. Treatment on page 156. Mentioned on page 155.

Plants usually acaulescent or nearly so (with dense rosettes of leaves and cluster of sessile or subsessile heads), less commonly caulescent and to 45 cm. Stems absent or short, stout, fleshy, usually unbranched, very leafy, villous or tomentose with septate trichomes. Leaves: blades linear to oblong, oblanceolate, or narrowly elliptic, pinnately lobed or often unlobed, longer spines slender or stout, usually 1 cm or less, sometimes unpigmented proximally or tinged pink or purplish, abaxial faces gray-tomentose with fine, non-septate trichomes and/or villous with septate trichomes, adaxial glabrous or thinly villous with septate trichomes. Heads 1–many, sessile or subsessile, crowded. Involucres 1.5–3 cm. Phyllaries: outer and mid lanceolate to ovate, spines slender to stout, 1–12 mm; apices of inner acuminate and entire or abruptly expanded into scarious, erose-toothed appendage. Corollas white or pink-tinged (rarely purple), 22–30 mm, tubes 11.5–16.5 mm, throats 5–10.5 mm, lobes 5–6.5 mm; style tips 3.5–6.5 mm. Cypselae 4.5–6 mm; pappi 20–25 mm. 2n = 34 (as C. foliosum).


Phenology: Flowering summer (Jun–Aug).
Habitat: Seasonally damp, sometimes saline soil in meadows, grasslands, open forests, sagebrush scrub
Elevation: 1100–3800 m

Distribution

V19-153-distribution-map.gif

Calif., Colo., Idaho, Nev., Oreg., Utah, Wyo., Mexico (Baja California)

Discussion

Variety americanum is a variable taxon widely distributed in mountains and valleys of the western United States from the eastern slope of the Cascades and Sierra Nevada across the northern Great Basin to the central Rocky Mountains. Within some populations dominated by acaulescent forms, occasional short, caulescent individuals or even taller plants may occur. These approach var. coloradense in the Colorado Rockies and resemble var. scariosum in the valleys of Oregon. Short caulescent individuals within populations of var. coloradense and var. scariosum approach var. americanum. Although the extremes are strikingly different, the genetic differences are apparently slight. Acaulescent individuals from the San Francisco Peaks and White Mountains of Arizona are treated here as var. coloradense. In the mountains of Colorado putative hybrids have been documented between Cirsium scariosum var. americanum and C. canescens and between C. scariosum var. americanum and C. undulatum.

Selected References

None.

Lower Taxa

None.

"fine" is not a number."narrower" is not a number."less" is not a number.

villous +  and glabrous +
short-tailed +
spineless +  and twisted +
erect +  and spreading +
innermost +
expanded +
scarious +
erose-toothed +
subcapitate +, racemiform +  and spiciform +
indeterminate +  and determinate +
David J. Keil +
(A. Gray) D. J. Keil +
winged-petiolate +  and sessile +
decurrent +
Cirsium acaule var. americanum +
compound +  and simple +
linear to elliptic +
5 cm50 mm <br />0.05 m <br /> (20 cm200 mm <br />0.2 m <br />) +
unlobed;lobed;linear;oblong oblanceolate or narrowly elliptic +
3cm;7cm +
10-nerved or 20-nerved +  and rugose +
tawny +  and white +
? (?) +  and ? (?) +
Dinnerplate or sessile or stemless thistle +
actinomorphic +
pink-tinged +  and white +
2.2 cm22 mm <br />0.022 m <br /> (3 cm30 mm <br />0.03 m <br />) +
light +  and dark-brown +
compressed +  and ovoid +
fertile +  and bisexual +
Calif. +, Colo. +, Idaho +, Nev. +, Oreg. +, Utah +, Wyo. +  and Mexico (Baja California) +
1100–3800 m +
gray-canescent +  and glabrous +
pistillate +, staminate +  and neuter +
winged +  and beaked +
dispersed +
Seasonally damp, sometimes saline soil in meadows, grasslands, open forests, sagebrush scrub +
subsessile +  and sessile +
indeterminate +
each +  and sessile +
2 cm20 mm <br />0.02 m <br /> (4 cm40 mm <br />0.04 m <br />) +
glabrate +  and arachnoid +
ovoid;hemispheric +
1.5 cm15 mm <br />0.015 m <br /> (3 cm30 mm <br />0.03 m <br />) +
1.5 cm15 mm <br />0.015 m <br /> (6 cm60 mm <br />0.06 m <br />) +
sessile +  and petiolate +
cauline +  and basal +
bristle-tipped +
lobed +, spinose-dentate +, linear-lanceolate +  and broadly triangular +
stout +  and slender +
1 cm10 mm <br />0.01 m <br /> (?) +
0.2 cm2 mm <br />0.002 m <br /> (1.5 cm15 mm <br />0.015 m <br />) +
entire +  and dentate +
scarious-fringed +  and entire +
rounded +
2-carpellate +
white +  and tan +
persistent +
2 cm20 mm <br />0.02 m <br /> (2.5 cm25 mm <br />0.025 m <br />) +
0 cm0 mm <br />0 m <br /> (10 cm100 mm <br />0.1 m <br />) +
Flowering summer (Jun–Aug). +
middle +  and outer +
weakly to strongly +
short-caulescent +  and acaulescent +
papillate +  and smooth +
bearing subulate enations +, hairy +  and bristly +
flat;convex +
glutinous +
tawny;white +
setiform +  and plumose +
exalbuminous +
subequal +
Illustrated +
erect +  and spreading +
flattened +
Slender (?) +  and Stout (?) +
0.1 cm1 mm <br />0.001 m <br /> (1.2 cm12 mm <br />0.012 m <br />) +
leafy +  and unbranched +
appendaged +  and truncate +
dilated +  and swollen +
enlarged +
0.35 cm3.5 mm <br />0.0035 m <br /> (0.65 cm6.5 mm <br />0.0065 m <br />) +
Cirsium acaulescens +, Cirsium americanum +, Cirsium coloradense subsp. acaulescens +, Cirsium coloradense subsp. longissimum +, Cirsium drummondii var. acaulescens +, Cirsium drummondii subsp. latisquamum +, Cirsium drummondii var. oregonense +, Cirsium drummondii subsp. vexans +  and Cirsium tioganum +
Cirsium scariosum var. americanum +
Cirsium scariosum +
variety +
cylindric +
expanded +
0.5 cm5 mm <br />0.005 m <br /> (1.05 cm10.5 mm <br />0.0105 m <br />) +
tipped +  and spineless +
scabro-denticulate +  and narrowed +
expanded +
bristly-dentate to coarsely +
septate +  and non-septate +
slender +
1.15 cm11.5 mm <br />0.0115 m <br /> (1.65 cm16.5 mm <br />0.0165 m <br />) +
taprooted +, caulescent +  and acaulescent +
perennial +  and biennial +
0 cm0 mm <br />0 m <br /> (200 cm2,000 mm <br />2 m <br />) +
caulescent +, nearly +  and acaulescent +