Cirsium mohavense

(Greene) Petrak

Bot. Tidsskr. 31: 68. 1911.

Common names: Mojave thistle
EndemicConservation concern
Basionym: Carduus mohavensis Greene Proc. Acad. Nat. Sci. Philadelphia 44: 361. 1893
Synonyms: Cirsium rusbyi (Greene) Petrak Cirsium virginense S. L. Welsh
Treatment appears in FNA Volume 19. Treatment on page 134. Mentioned on page 108.

Biennials or perennials, 30–250 cm; taprooted. Stems 1–several, erect, proximally simple, distally branched, ± densely gray-tomentose; branches 0–many, ascending to spreading. Leaves: blades oblongelliptic to oblanceolate, 10–60 × 2–15 cm, unlobed and merely spinulose or spiny-dentate or shallowly to deeply pinnatifid, lobes linear-lanceolate to ovate-triangular, spreading, entire to coarsely dentate, main spines slender to stout, 3–30 mm, faces ± gray-tomentose, sometimes ± glabrate; basal often present at flowering, winged-petiolate; principal cauline decreasing distally, proximal winged-petiolate, distal sessile, bases decurrent as spiny wings 1–5 cm; distalmost well separated, bractlike. Heads 1–many, in corymbiform or paniculiform arrays. Peduncles 0–15 cm. Involucres ovoid to hemispheric, 1.5–2.5 × 1.5–2 cm, loosely arachnoid on phyllary margins or glabrate. Phyllaries in 5–8 series, imbricate, (inner greenish to brown or stramineous), lanceolate or ovate (outer) to linear-lanceolate (inner), entire, abaxial faces with narrow glutinous ridge; outer and middle appressed, spines spreading, 3–7 mm; apices of inner often flexuous, flattened, spineless, scabrid. Corollas white to pink or lavender, 16–25 mm, tubes 7–12 mm, throats 4–7 mm, lobes 4–8 mm, style tips 3–4 mm. Cypselae stramineous to dark-brown, 3–6 mm, apical collars 0.2–0.3 mm, yellowish; pappi 14–16 mm. 2n = 30, 32.


Phenology: Flowering summer–fall (Jun–Oct).
Habitat: Wet soil, streams, springs, meadows in desert and desert woodland areas
Elevation: -50–2200 m

Distribution

V19-107-distribution-map.gif

Ariz., Calif., Nev., Utah.

Discussion

Of conservation concern.

Cirsium mohavense ranges from scattered sites in eastern California east in the Basin and Range Province of southern Nevada to southwestern Utah and nortwestern Arizona, mostly in Mojave Desert region. When Welsh proposed Cirsium virginense for a geographically limited group of plants from southwestern Utah and northwestern Arizona (and subsequently discovered in extreme southeastern Nevada), he indicated that its relationship to other western thistles was unknown. Subsequently, he indicated (S. L. Welsh 1983; Welsh et al. 1993) that the affinities of the taxon apparently lie with C. mohavense, but he did not attempt to distinguish C. virginense from C. mohavense (in the strict sense) because the latter was not known to occur in Utah. A. Cronquist (1994) attempted the distinction. The only character he used in his key was life span of the plants: biennial (C. mohavense) versus perennial, spreading by creeping roots (C. virginense). In the descriptions of the two taxa he elaborated on this character, indicating that C. mohavense is single-stemmed and C. virginense often multistemmed. In the remaining features the plants are very similar or overlap extensively.

Distinction of two taxa on the basis of duration is impractical and probably inaccurate. Specimens commonly lack roots, and in those specimens in which bases are present, I have seldom been able to make any distinction between biennial taproots and perennial taproots. In particular I have seen no evidence of creeping roots. I am not aware of any study of either taxon that documents the life history of the plants. Some specimens of C. mohavense (in the strict sense) appear to have perennial bases like those attributed to C. virginense by Cronquist. For instance, a specimen of C. mohavense from Death Valley (Thorne & Ratcliff 2287, BRY) is indistinguishable from specimens of C. virginense (e.g., Atwood 13374, BRY) from Nevada and Utah. Both have a branched root crown with multiple rosettes and nearly identical leaves and heads.

Selected References

None.

Lower Taxa

None.

"fine" is not a number.

... more about "Cirsium mohavense"
short-tailed +
spineless +  and twisted +
dentate +, entire +  and spine-tipped +
erect +  and spreading +
innermost +
scarious +
0.02 cm0.2 mm <br />2.0e-4 m <br /> (0.03 cm0.3 mm <br />3.0e-4 m <br />) +
paniculiform +  and corymbiform +
indeterminate +  and determinate +
David J. Keil +
(Greene) Petrak +
winged-petiolate +
decurrent +
Carduus mohavensis +
compound +  and simple +
10 cm100 mm <br />0.1 m <br /> (60 cm600 mm <br />0.6 m <br />) +
unlobed;oblongelliptic;oblanceolate +
2cm;15cm +
10-nerved or 20-nerved +  and rugose +
ascending;spreading +
tawny +  and white +
Mojave thistle +
actinomorphic +
white +  and pink or lavender +
1.6 cm16 mm <br />0.016 m <br /> (2.5 cm25 mm <br />0.025 m <br />) +
stramineous +  and dark-brown +
compressed +  and ovoid +
fertile +  and bisexual +
Ariz. +, Calif. +, Nev. +  and Utah. +
-50–2200 m +
glabrate +  and gray-tomentose +
pistillate +, staminate +  and neuter +
winged +  and beaked +
dispersed +
Wet soil, streams, springs, meadows in desert and desert woodland areas +
indeterminate +
each +  and sessile +
1.5 cm15 mm <br />0.015 m <br /> (2.5 cm25 mm <br />0.025 m <br />) +
glabrate +  and arachnoid +
ovoid;hemispheric +
1.5 cm15 mm <br />0.015 m <br /> (2 cm20 mm <br />0.02 m <br />) +
sessile +  and petiolate +
cauline +  and basal +
bristle-tipped +
entire +  and coarsely dentate +
linear-lanceolate +  and ovate-triangular +
0.3 cm3 mm <br />0.003 m <br /> (3 cm30 mm <br />0.03 m <br />) +
entire +  and dentate +
usually lobed +  and dissected +
2-carpellate +
persistent +
1.4 cm14 mm <br />0.014 m <br /> (1.6 cm16 mm <br />0.016 m <br />) +
0 cm0 mm <br />0 m <br /> (15 cm150 mm <br />0.15 m <br />) +
Flowering summer–fall (Jun–Oct). +
middle +  and outer +
weakly to strongly +
papillate +  and smooth +
Bot. Tidsskr. +
bearing subulate enations +, hairy +  and bristly +
flat;convex +
glutinous +
tawny;white +
setiform +  and plumose +
exalbuminous +
subequal +
Endemic +  and Conservation concern +
0.3 cm3 mm <br />0.003 m <br /> (0.7 cm7 mm <br />0.007 m <br />) +
branched +  and simple +
1 +  and several +
appendaged +  and truncate +
dilated +  and swollen +
enlarged +
0.3 cm3 mm <br />0.003 m <br /> (0.4 cm4 mm <br />0.004 m <br />) +
Cirsium rusbyi +  and Cirsium virginense +
Cirsium mohavense +
species +
cylindric +
expanded +
0.4 cm4 mm <br />0.004 m <br /> (0.7 cm7 mm <br />0.007 m <br />) +
bristly-dentate to coarsely +
slender +
0.7 cm7 mm <br />0.007 m <br /> (1.2 cm12 mm <br />0.012 m <br />) +
perennial +  and biennial +
30 cm300 mm <br />0.3 m <br /> (250 cm2,500 mm <br />2.5 m <br />) +
tree +, vine +, shrub +  and subshrub +
1 cm10 mm <br />0.01 m <br /> (5 cm50 mm <br />0.05 m <br />) +