Cirsium tracyi |
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Tracy's thistle |
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Habit | Perennials, 50–200+ cm; tap-rooted. |
Stems | 1–several, erect or ascending, thinly gray-tomentose or ± glabrate; branches few to many, ascending. |
Leaves | blades elliptic to oblong, 8–40 × 1–12 cm, margins weakly to strongly undulate, spinose-dentate or shallowly to deeply lobed, lobes ascending to spreading, ± triangular, mostly well separated, spinulose and coarsely dentate or cleft into 2–3 lanceolate to triangular, often entire-margined, spine-tipped divisions, main spines 2.5–7+ mm, abaxial faces densely gray-tomentose, adaxial thinly tomentose; basal sometimes present at flowering, winged-petiolate; principal cauline becoming sessile and progressively reduced distally, widest at bases, bases ± auriculate-clasping to short-decurrent; distal cauline reduced, often spinier. |
Peduncles | 0–10+ cm. |
Involucres | ovoid to hemispheric or broadly campanulate, 2–3 × 1.7–3.5 cm, loosely arachnoid on phyllary margins or glabrate. |
Corollas | white to lavender or pink-purple, 23–30 mm, tubes 9–14 mm, throats 5.5–10.5 mm, lobes 5.5–9.5 mm; style tips 4–7 mm. |
Phyllaries | in 6–10 series, imbricate, ovate to lanceolate (outer) to linear-lanceolate (inner), margins entire, abaxial faces with prominent glutinous ridge; outer and middle appressed, spines spreading, slender to stout, 2–6 mm; apices of inner often flexuous, narrow, flat, ± entire, spineless or tipped with weak spines. |
Heads | 1–many, terminal on branches and often in leaf axils, in leafy, ± corymbiform arrays. |
Cypselae | light to dark brown, 6–7 mm, apical collars colored like body or rarely yellowish, narrow; pappi 20–23 mm, usually noticeably shorter than corolla. |
2n | = 24. |
Cirsium tracyi |
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Phenology | Flowering late spring–summer (Jun–Aug). |
Habitat | Dry slopes, sagebrush deserts, pinyon-juniper woodlands, openings in montane coniferous forests, often in disturbed areas |
Elevation | 1400–2900 m (4600–9500 ft) |
Distribution |
CO; NM; UT
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Discussion | Cirsium tracyi occurs from eastern Utah and western Colorado south in the Colorado Plateau and southern Rocky Mountains to northwestern New Mexico. Large-headed plants of Cirsium tracyi and small-headed individuals of C. undulatum are sometimes difficult to distinguish. P. L. Barlow-Irick (unpubl.) found that although there is much overlap in floral measurements of C. tracyi and C. undulatum, the means for some of these characters are statistically significant. Corolla lobes of C. tracyi, for instance, average about 7 mm and those of C. undulatum about 10 mm. The species differ in chromosome number as well. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 19, p. 121. |
Parent taxa | Asteraceae > tribe Cardueae > Cirsium |
Sibling taxa | |
Synonyms | Carduus tracyi, C. acuatum, C. floccosum, C. undulatus var. tracyi |
Name authority | (Rydberg) Petrak: Beih. Bot. Centralbl. 35(2): 424. (1917) |
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