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Published In: The Gardeners Dictionary...Abridged...fourth edition 1:. 1754. (Gard. Dict. Abr. (ed. 4)) Name publication detail
 

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30. Cirsium Mill. (thistle)

Plants biennial or perennial. Stems erect, branched or less commonly unbranched, in some species noticeably spiny-winged, in unwinged species angled or ridged, variously glabrous or hairy. Leaves basal and alternate, spiny along the margins, usually densely pubescent with white, woolly hairs on both surfaces or only the undersurface, those of the basal rosette with the margins scalloped or toothed but often unlobed, the stem leaves often pinnately lobed, in wing-stemmed species the leaf bases decurrent along the stem, the wings wavy or scalloped to evenly lobed, spiny along the margins. Inflorescences terminal on the branches, the heads long-stalked to nearly sessile, solitary or in small clusters at the branch tips. Heads discoid, the involucre variously shaped, the florets all appearing similar and perfect (or the plants incompletely dioecious in C. arvense). Receptacle flat or short-conical, with numerous bristles. Involucral bracts (except sometimes the innermost ones) tapered to a spiny tip (spineless or nearly so in C. muticum). Pappus of numerous often unequal, long bristles (the marginal florets sometimes with somewhat fewer, less plumose bristles), these fused at the base, plumose (featherlike with numerous long, capillary side branches), shed more or less as a unit before fruiting. Corollas cream-colored or pink to purple, rarely white. Fruits appearing basally or more commonly somewhat obliquely attached, oblong or slightly narrower at the usually somewhat asymmetrical base, often slightly curved or arched in profile, somewhat flattened and sometimes slightly 4-angled in cross-section, the tip usually with an angular rim or raised crown surrounding a small, knoblike or conical projection, the surface somewhat shiny, straw-colored or light brown, grayish brown or brown. Two hundred to 350 species, widespread in the Northern Hemisphere.

In addition to the species treated below, C. hillii (Canby) Fernald (C. pumilum ssp. hillii (Canby) R.J. Moore & Frankton) should be searched for in eastern Missouri. Steyermark (1963) misdetermined two historical specimens of this taxon from the St. Louis metropolitan region as C. pumilum (Nutt.) Spreng. but correctly noted that they were actually collected in St. Clair County, Illinois. On that basis, he excluded these specimens from the Missouri flora. In 1979, Marlin L. Bowles of the Morton Arboretum (Lisle, Illinois) photographed a plant of probable C. hillii in a small remnant upland prairie strip between a road and a railroad near the town of Ely in Ralls County. However, the photographs were insufficient in detail to confirm with certainty the identity of the species. Perhaps because of construction in the vicinity, repeated attempts by several botanists to relocate Hill’s thistle at this site have failed. The main distribution of C. hillii is to the north and east of Missouri (Moore and Frankton, 1966), but western Illinois populations are known from sites immediately adjacent to northeastern Missouri. The species will not key well below. Cirsium hillii is a perennial with long, thickened, hollow roots giving rise to stout stems. The stem leaves are generally narrowly oblong-elliptic, pinnately lobed with relatively short, irregularly triangular lobes, and with the undersurface finely hairy or cobwebby, but the green color not persistently hidden by the pubescence. The heads are relatively large, with the involucre 3.5–5.0 cm long and the narrow involucral bracts having a slender, sticky dorsal ridge (the outer and median ones are tapered to a short, slender, ascending, spiny tip).

In most of our thistles, the heads are subtended by one to several small leaves and thus appear sessile or short-stalked. Unlike the situation in some western species, these leaves are relatively small and few-lobed in the taxa occurring in Missouri. In C. carolinianum, the accessory leaves are highly reduced and widely spaced along the long stalk, and the heads thus appear long-stalked.

 

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1 1. Leaf bases long-decurrent (more than 1 cm), the stems with spiny-margined wings, at least above the midpoint

2 2. Leaf blades with the upper surface pubescent with felty (when young) to cobwebby hairs, not roughened, the undersurface densely pubescent with white, woolly to felty hairs; corollas cream-colored, rarely pale pink ... 3. C. CANESCENS

Cirsium canescens
3 2. Leaf blades with the upper surface strongly roughened with numerous short, stiff, spinelike or barblike bristles, not cobwebby-hairy, the undersurface thinly or finely pubescent with cobwebby hairs; corollas reddish purple to purple ... 9. C. VULGARE

Cirsium vulgare
4 1. Leaf bases not or only short-decurrent, the stems not winged

5 3. None of the involucral bracts spiny at the tip, at most tapered to a minute, sharp point

6 4. Heads usually in loose clusters at the branch tips; involucre 1020 mm long, plants incompletely dioecious (some plants with only pistillate florets, others with a combination of staminate and perfect florets); perennials, colonial from widely creeping, deep-set, black roots ... 2. C. ARVENSE

Cirsium arvense
7 4. Heads solitary at the branch tips; involucre (17)2035 mm long; plants with the florets all perfect; biennial, with a cluster of stout, white to brown roots ... 6. C. MUTICUM

Cirsium muticum
8 3. At least the lower and median involucral bracts spiny at the tip

9 5. Stem leaves all unlobed or shallowly lobed (less than 1/3 of the way from the margin to midrib), the reduced leaves just below the heads rarely more deeply lobed

10 6. Leaves mostly basal or along the lower 1/3 of the stem, few and much-reduced in size toward the stem tip, the heads thus appearing long-stalked; involucre 1520 mm long ... 4. C. CAROLINIANUM

Cirsium carolinianum
11 6. Leaves well developed along the stem, those toward the branch tips somewhat reduced in size, the heads appearing sessile or very short-stalked; involucre 2545 mm long

12 7. Stems glabrous or sparsely pubescent with spreading hairs, sometimes with patches of white, woolly to felty hairs toward the tip; leaves with the upper surface green with sparse to moderate, stiff, straight hairs, often becoming nearly glabrous with age, the undersurface densely and persistently pubescent with white, felty hairs ... 1. C. ALTISSIMUM

Cirsium altissimum
13 7. Stems densely pubescent with persistent, white, woolly to felty hairs; leaves with both surfaces appearing grayish or whitish with relatively dense, woolly hairs, the pubescence sometimes becoming thinner on both surfaces with age (the leaves still appearing uniformly gray to grayish green) ... 8. C. UNDULATUM

Cirsium undulatum
14 5. Most or all of the leaves deeply lobed (more than 1/2 of the way from the margin to midrib)

15 8. Involucre 2535 mm long; heads appearing sessile or very short-stalked, the branch tips with reduced leaves ... 5. C. DISCOLOR

Cirsium discolor
16 8. Involucre 1522 mm long; heads appearing relatively long-stalked, the leaves strongly reduced in size above the stem midpoint, few and scattered toward the tip of the stem or branches

17 9. Largest leaves narrowly lanceolate to linear, at most with a few narrow lobes, long-tapered at the base, not decurrent; plants with a short, inconspicuous taproot in addition to the often somewhat thickened, fibrous roots ... 4. C. CAROLINIANUM

Cirsium carolinianum
18 9. Largest leaves narrowly ovate to elliptic or broadly oblanceolate, with several pairs of relatively broad lobes, rounded at the base and somewhat clasping the stem, often short-decurrent; plants with a well-developed taproot, this usually strongly thickened and larger than the fibrous roots ... 7. C. TEXANUM Cirsium texanum var. texanum
 
 
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