Cirsium mohavense
Cirsium carolinianum
Mohave thistle, Mojave thistle, Rusby's thistle, virgin thistle
Carolina or purple or soft or smallhead thistle, Carolina thistle, soft thistle
1–several, erect, proximally simple, distally branched, ± densely gray-tomentose;
branches 0–many, ascending to spreading.
usually single, erect, glabrous to ± tomentose, sometimes sparsely villous with septate trichomes;
branches few, usually distal, 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 linear to oblanceolate or elliptic, 10–30 × 1–5 cm, unlobed and spinulose to irregularly dentate or pinnatifid, lobes narrowly to broadly triangular, sometimes coarsely toothed or lobed toward base, acuminate, main spines slender, 1–5 mm, abaxial faces gray-tomentose, adaxial glabrous or sparsely villous with septate trichomes;
basal often present at flowering, petioles slender, winged, bases long-tapered;
principal cauline relatively few (10–25), petiolate or distal sessile, mostly restricted to proximal 1/2 of stems, progressively reduced distally, bases tapered, not decurrent;
distal cauline widely separated, linear to narrowly elliptic, reduced, becoming ± bractlike, merely spinulose to irregularly dentate or shallowly lobed.
0–15 cm.
slender, 1–15 cm (not overtopped by distal leaves).
ovoid to hemispheric, 1.5–2.5 × 1.5–2 cm, loosely arachnoid on phyllary margins or glabrate.
narrowly ovoid to campanulate, 1.2–2 × 1.2–2 cm, thinly arachnoid-ciliate.
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.
pink-purple (white), 15–20 mm, tubes 5–9 mm, throats 5–7 mm (noticeably wider than tubes), lobes 4–5 mm;
style tips 4 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, imbricate, green, linear to lanceolate (outer) or linear to linear-lanceolate (inner), abaxial faces with narrow, glutinous ridge;
outer and middle ascending to appressed, bodies entire, apices widely spreading (at least the outer), spines ascending to spreading (at least the outer), slender, 1–4 mm;
apices of inner phyllaries flat, often twisted, acuminate.
1–many, in corymbiform or paniculiform arrays.
(1–)2–9(–many), in paniculiform arrays.
stramineous to dark brown, 3–6 mm, apical collars 0.2–0.3 mm, yellowish;
pappi 14–16 mm.
light brown, 3–4 mm, apical collars yellowish, 0.5–1 mm;
pappi 12–14 mm.
= 30, 32.
= 20, 22.
Cirsium mohavense
Cirsium carolinianum
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 carolinianum is widely distributed in the southeastern United States: on the Gulf coastal plain from Texas to Alabama north through the Ouachita and Ozark highlands to southeastern Missouri; in the Ohio River Valley from southernmost Illinois to southern Ohio and northern Kentucky; and in the southern Appalachians and Piedmont from Alabama and Tennessee to southern Virginia. Cirsium carolinianum, though widespread, is a taxon of conservation concern over part of its range. The replacement of open woods by dense forests brought about by fire suppression has greatly reduced available habitat.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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