Cirsium altissimum
Cirsium pitcheri
roadside thistle, tall thistle
dune thistle, Pitcher's thistle, sand-dune thistle
single, erect, villous with septate trichomes, sometimes ± glabrate, sometimes distally thinly tomentose;
branches few–many, ascending.
1 or few, erect, densely gray-tomentose;
branches 0 to several, ascending to spreading.
blades oblanceolate to elliptic or ovate, 10–40 × 1–13 cm, margins flat, finely spiny-toothed and otherwise undivided to coarsely toothed or shallowly pinnatifid, lobes broadly triangular, main spines 1–5 mm, abaxial faces white-tomentose, adaxial faces green, glabrate to villous with septate trichomes;
basal usually absent at flowering, winged-petiolate, bases tapered;
principal cauline well distributed, gradually reduced, bases narrowed, sometimes weakly clasping;
distal cauline well developed.
blades elliptic to obovate, 10–30 × 8–14 cm, deeply divided nearly to midveins, lobes ascending to spreading, linear, remote, margins revolute, entire or minutely spinulose, main spines 1–2 mm, faces gray-tomentose, more densely so abaxially;
basal present or withered at flowering, petiolate;
principal cauline well distributed, bases decurrent as linear-lobed to spiny wings 1–3 cm;
distal cauline well developed.
0–5 cm (leafy-bracted).
0–5 cm.
ovoid to broadly cylindric or campanulate, (2–)2.5–3.5(–4) × (1.5–)2–3(–4) cm, thinly arachnoid.
ovoid to campanulate, 2–3 × 2–3 cm, loosely arachnoid on phyllary margins or glabrate.
tips 4–6 mm.
pink to purple (white), 20–35 mm, tubes 10–16 mm, throats 5–12 mm, lobes 5–9 mm.
dull white or pinkish-tinged (rarely rich purple), 20–30 mm, tubes 8.5–15 mm, throats 4.5–10 mm, lobes 3–8 mm;
style tips 3.5–5.5 mm.
in 10–20 series, strongly imbricate, greenish with subapical darker central zone, ovate (outer) to lanceolate (inner), abaxial faces with a narrow glutinous ridge (milky when fresh, dark when dry), outer and middle entire, bodies appressed, spines slender, abruptly spreading, 3–4 mm;
apices of inner phyllaries spreading, narrow, flattened, entire, spines spreading, slender, 3–4 mm;
apices of inner phyllaries spreading, narrow, flattened, ± dilated, ± erose or finely serrulate.
in 6–8 series, imbricate, ovate-lanceolate (outer) to linear-lanceolate (inner), abaxial faces with narrow glutinous ridge;
outer and middle appressed, acute, spines ascending to spreading, slender, 1–2(–3) mm;
apices of inner often flexuous, flattened, spineless, scabrid.
1–many, in corymbiform or paniculiform arrays, (± elevated above principal cauline leaves), not subtended by ring of spiny bracts.
1–20+ in corymbiform arrays.
tan to dark brown, 4–5.5 mm, apical collars stramineous, 0.5–1 mm;
pappi 12–24 mm.
light brown, sometimes with darker streaks, 6–7.5 mm, apical collars lighter colored, very narrow;
pappi 15–30 mm, usually noticeably shorter than corolla.
= 18.
= 34.
Cirsium altissimum
Cirsium pitcheri
Plants of Cirsium altissimum ranging from southern Minnesota to Texas often have more deeply divided leaves than do populations in other portions of the species’ range. Some botanists (e.g., R. J. Moore and C. Frankton 1969; D. S. Correll and M. C. Johnston 1970) have treated those plants as C. iowense. Others (e.g., R. E. Brooks 1986; H. A. Gleason and A. Cronquist 1991; G. B. Ownbey and T. Morley 1991) have treated them as C. altissimum. Still others considered them to be derivatives of hybridization between C. altissimum and C. discolor (J. T. Kartesz and C. A. Meacham 1999) and treated them as C. ×iowense. Indeed the existence of these plants blurs the distinction between C. altissimum and C. discolor, and herbarium specimens are often difficult to assign.
Natural hybrids between Cirsium altissimum and C. discolor are well documented (R. A. Davidson 1963; G. B. Ownbey and Hsi Y.-T. 1963; Ownbey 1964; S. Dabydeen 1997). Ownbey and Dabydeen both reported that apparent F1 hybrids between the two species have low seed set in comparison with the parental taxa. W. L. Bloom (1977) reported that the chromosomes of the two species differ by several rearareaments. Dabydeen reported a count of 2n = 19 with multiple meiotic irregularities for an apparent F1 hybrid. However, the presence of numerous individuals and populations seemingly intermediate between C. altissimum and C. discolor indicates that although F1 hybrids have low fertility, long-term processes may have stabilized hybrid derivatives of higher fertility. Ownbey and Hsi reported mitotic counts of 2n = 18 and 20 from a population that they treated as C. altissimum. In their discussion they noted that their plants represented “the segregate called C. iowense” and had been collected a short distance from that taxon’s type locality. R. J. Moore and C. Frankton (1969) reported a chromosome number of 2n = 18 for a plant from Texas that they considered to be C. iowense. Further investigation of morphologic variation, chromosome number, meiotic behavior, and fertility is needed of populations named as C. iowense to determine how those plants should be treated.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Cirsium pitcheri is endemic to beach and dune habitats around lakes Huron, Michigan, and Superior. It has been extirpated from portions of its former range at the southern end of Lake Michigan. It is threatened by foot traffic, off-road vehicular activity, and clearing and development of beachside habitats. It is in the Center for Plant Conservation’s National Collection of Endangered Plants.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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