Cirsium mohavense
Cirsium quercetorum
Mohave thistle, Mojave thistle, Rusby's thistle, virgin thistle
Alameda County thistle, brownie or Alameda County thistle, brownie thistle
1–several, erect, proximally simple, distally branched, ± densely gray-tomentose;
branches 0–many, ascending to spreading.
1–10+, erect or ascending, glabrous to thinly gray-tomentose, sometimes villous with septate trichomes;
branches 0 or few, ascending.
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 elliptic to obovate, 5–20 × 3–7 cm, strongly undulate, shallowly to deeply pinnatifid with 3–8 pairs of lobes, lobes linear-lanceolate to broadly triangular, (often longer than 2 cm), closely spaced, spreading, spinose-dentate or lobed, main spines slender to stout, 2–15 mm, abaxial faces thinly to densely tomentose, ± villous with septate trichomes along veins, glabrescent or trichomes persistent, adaxial thinly arachnoid-tomentose and soon glabrescent;
basal usually present at flowering, petiolate;
principal cauline petiolate, progressively reduced distally, bases sometimes decurrent as spiny wings to 1 cm;
distal reduced, similar to proximal.
0–15 cm.
0–10 cm, leafy-bracted.
ovoid to hemispheric, 1.5–2.5 × 1.5–2 cm, loosely arachnoid on phyllary margins or glabrate.
ovoid to hemispheric or broadly campanulate, 2.5–5 (in first-formed heads, often smaller in later heads) × 2.5–6 cm, loosely arachnoid on phyllary margins 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 or pale lavender to purple, 25–35 mm, tubes 10–20 mm, throats 7–10 mm, lobes 5–8 mm;
style tips 2.5–4.5 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 5–10 series, imbricate, ovate or lanceolate (outer) to linear-lanceolate (inner), margins of outer entire, abaxial faces without glutinous ridge;
outer and mid appressed, spines erect or ascending, (0–)1–2(–10) mm;
apices of mid and inner narrowed and scabrido-denticulate or with expanded, spinuloso-serrate or -dentate tips, spineless or spine-tipped.
1–many, in corymbiform or paniculiform arrays.
1–few, erect, ± crowded, often closely subtended by distalmost leaves.
stramineous to dark brown, 3–6 mm, apical collars 0.2–0.3 mm, yellowish;
pappi 14–16 mm.
brown, 5–6.5 mm, apical collars colored like body;
pappi 20–40 mm.
= 30, 32.
= 32.
Cirsium mohavense
Cirsium quercetorum
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.)
Cirsium quercetorum occurs in the north and south Coast ranges of California from Mendocino to San Luis Obispo counties. It overlaps in range and habitat with several other thistle species and has been reported to hybridize with C. andrewsii, C. douglasii, C. occidentale, C. remotifolium var. odontolepis, and C. fontinale var. fontinale (F. Petrak 1917; J. T. Howell 1960b). Considerable variation occurs within the range of C. quercetorum, and two of the variants have been given taxonomic recognition as vars. walkerianum and xerolepis. Additional study over the range of the species is needed to determine whether these or other variants should be recognized formally.
Cirsium quercetorum appears to be related to the polymorphic C. scariosum complex. The perennial habit with runner roots of C. quercetorum consistently distinguishes it from the monocarpic C. scariosum.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
CA
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