Cirsium altissimum |
Cirsium rydbergii |
|
---|---|---|
roadside thistle, tall thistle |
alcove thistle, Rydberg's thistle |
|
Habit | Biennials or short-lived monocarpic perennials, (50–)100–300(–400) cm; taproots and often a cluster of coarse fibrous roots, roots without tuberlike enlargements. | Perennials, 100–300 cm; caudices and taproots, spreading by creeping roots. |
Stems | single, erect, villous with septate trichomes, sometimes ± glabrate, sometimes distally thinly tomentose; branches few–many, ascending. |
1–several, erect or ascending to lax and hanging, glabrous or thinly tomentose; branches 0–few, ascending. |
Leaves | 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, 30–90+ × 10–40 cm, 1–2 times pinnately lobed, lobes linear to ovate, strongly undulate, main spines slender, 5–15 mm, faces often glaucous, glabrous or thinly tomentose and soon glabrescent; basal present at flowering, petiolate or winged-petiolate; proximal cauline winged-petiolate; mid sessile, much reduced, less deeply lobed, bases clasping, short-decurrent 0–2 cm; distal linear or lanceolate, bractlike, very spiny. |
Peduncles | 0–5 cm (leafy-bracted). |
0.5–6 cm. |
Involucres | ovoid to broadly cylindric or campanulate, (2–)2.5–3.5(–4) × (1.5–)2–3(–4) cm, thinly arachnoid. |
hemispheric, 1.4–2 × 1–2 cm, phyllary margins thinly tomentose or glabrate. |
Style | tips 4–6 mm. |
|
Corollas | pink to purple (white), 20–35 mm, tubes 10–16 mm, throats 5–12 mm, lobes 5–9 mm. |
dull white to pink or purple, 16–20 mm, tubes 7–8.5 mm, throats 4–6.5 mm, lobes 4.5–6 mm; style tips 2.5 mm. |
Phyllaries | 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 5–8 series, strongly imbricate, (green, drying green or light brown), ovate to lance-oblong, abaxial faces with or without poorly developed glutinous ridge; outer and mid bases appressed, margins entire, not scabridulous-ciliolate, apices spreading or reflexed, green to brownish, lance-ovate, elongate, flattened, spines slender, 3–25 mm; apices of inner straight, entire. |
Heads | 1–many, in corymbiform or paniculiform arrays, (± elevated above principal cauline leaves), not subtended by ring of spiny bracts. |
few–many, erect or nodding in clusters at tips of distal branches in paniculiform arrays, not closely subtended by clustered leafy bracts. |
Cypselae | tan to dark brown, 4–5.5 mm, apical collars stramineous, 0.5–1 mm; pappi 12–24 mm. |
gray or brown, 3.7–4.5 mm, apical collars not differentiated; pappi 10–15 mm. |
2n | = 18. |
= 34. |
Cirsium altissimum |
Cirsium rydbergii |
|
Phenology | Flowering summer–fall (Jun–Oct). | Flowering spring–summer (May–Sep). |
Habitat | Prairies, woodlands, disturbed sites, often in damp soil | Hanging gardens, seeps, stream banks |
Elevation | 50–700 m (200–2300 ft) | 1000–1500 m (3300–4900 ft) |
Distribution |
AL; AR; DC; DE; FL; GA; IA; IL; IN; KS; KY; LA; MA; MD; MI; MN; MO; MS; NC; ND; NE; NY; OH; OK; PA; SC; SD; TN; TX; WI; WV
|
AZ; UT |
Discussion | 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 rydbergii is endemic to the Colorado Plateau of northern Arizona and southeastern Utah. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 19, p. 111. | FNA vol. 19, p. 162. |
Parent taxa | Asteraceae > tribe Cardueae > Cirsium | Asteraceae > tribe Cardueae > Cirsium |
Sibling taxa | ||
Synonyms | Carduus altissimus, C. altissimum var. biltmoreanum, C. iowense | C. lactucinum |
Name authority | (Linnaeus) Sprengel: Syst. Veg. 3: 373. (1826) | Petrak: Beih. Bot. Centralbl. 35(2): 315. (1917) |
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