Cirsium mohavense
Cirsium occidentale
Mohave thistle, Mojave thistle, Rusby's thistle, virgin thistle
cobwebby thistle, snowy thistle, Venus thistle, western thistle
1–several, erect, proximally simple, distally branched, ± densely gray-tomentose;
branches 0–many, ascending to spreading.
usually 1, thinly to densely gray- or white-tomentose, sometimes ± glabrate;
branches few–many, usually from above mid or near base in compact, moundlike dwarf plants, ascending to spreading.
blades oblong-elliptic 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.
blades oblong–elliptic to oblanceolate, 6–40 × 1.5–10+ cm, shallowly to deeply pinnatifid, lobes usually rigidly spreading, undivided or with 1–2 pairs of coarse teeth or lobes, main spines 5–15 mm, both faces gray- to white-tomentose, sometimes ± glabrate or adaxial faces green, thinly arachnoid-tomentose;
basal sometimes present at flowering, petiolate or sessile and bases tapered, spiny-winged;
principal cauline much reduced distally, sessile, bases decurrent or not, as spiny wings;
distal much reduced, linear, ± bractlike.
0–15 cm.
1–30 cm.
ovoid to hemispheric, 1.5–2.5 × 1.5–2 cm, loosely arachnoid on phyllary margins or glabrate.
ovoid to spheric, 1.5–5 × 1.5–8 cm, arachnoid to ± loosely tomentose, often adjacent phyllaries connected by conspicuous arachnoid trichomes, sometimes glabrous or glabrate.
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.
white to lavender, pink, rose-purple, or red, 18–40 mm, tubes 8–18 mm, throats 5–7 mm, lobes 5–10 mm;
style tips 4–5 mm.
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.
in 7–10 series, subequal to strongly imbricate, green or stramineous to purple-tinged, linear to narrowly lanceolate, abaxial faces without glutinous ridge;
outer and mid bodies appressed, entire, apices deflexed to spreading or ascending, short-triangular to elongate, linear-acicular, spines spreading to reflexed, 1–10+ mm;
apices of inner erect, often flexuous, flat.
1–many, in corymbiform or paniculiform arrays.
1–many in loose to tight clusters (barely raised above rosette in dwarf plants).
stramineous to dark brown, 3–6 mm, apical collars 0.2–0.3 mm, yellowish;
pappi 14–16 mm.
± brown, 5–6 mm, apical collars not differentiated;
pappi 15–30 mm.
= 30, 32.
Cirsium mohavense
Cirsium occidentale
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Varieties 7 (7 in the flora).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Plants compact, rounded, moundlike; heads usually not much elevated above leaves | var. compactum |
1. Plants usually erect; principal heads usually conspicuously pedunculate | → 2 |
2. Corollas white to light purple or rose | var. californicum |
2. Corollas deep purple to bright pink or red | → 3 |
3. Plants densely white-tomentose; phyllaries persistently white-tomentose (except spines); outer phyllaries usually very long, spreading to reflexed | var. candidissimum |
3. Plants variably tomentose, sometimes ± glabrate; phyllaries ± arachnoid to floccose-tomentose, sometimes green and glabrate; outer phyllaries short to long, ascending to spreading or reflexed | → 4 |
4. Involucres usually about as long as wide or wider than long; phyllaries densely and persistently arachnoid with fine trichomes connecting tips of adjacent phyllaries | → 5 |
4. Involucres usually longer than wide; phyllaries tomentose or glabrate, sparingly or not arachnoid with fine trichomes connecting tips of adjacent phyllaries | → 6 |
5. Phyllary apices ± imbricate, the proximal usually shorter than medial and distal, lanceolate to linear-acicular, 0.5–15 mm; co- rollas bright purple | var. occidentale |
5. Phyllary apices subequal, all long- acicular, 1.5–3 cm; corollas light to deep reddish purple | var. coulteri |
6. Corollas 20–24 mm, deep reddish purple; s Santa Lucia Mountains of San Luis Obispo County, California | var. lucianum |
6. Corollas 23–35 mm, bright pink to red; widespread | var. venustum |
CA
WildflowerSearch
iNaturalist
USDA Plants Database
OR
Flora NW
PNW Herbaria
