Carduus nutans
Carduus crispus
chardon penché, common harebell, musk thistle, nodding plumeless-thistle, nodding thistle
chardon crépu, curled thistle, curly plumeless-thistle, welted thistle
glabrous to tomentose;
teeth of wings to 10 mm, wing spines 2–10 mm.
openly branching, villous with curled, septate hairs to nearly glabrous, spiny wings to 1.5 cm wide, wing spines to 3 mm.
basal tapering to winged petioles, blades 10–40 cm, margins 1–2x-pinnately lobed;
cauline sessile, shorter, margins less divided, glabrous or ± hairy.
basal tapering to winged petioles, blades 10–20 cm, margins spiny-toothed to ± shallowly pinnately lobed;
cauline sessile, gradually smaller, margins often more deeply divided, marginal spines to 3 mm;
abaxial leaf faces ± tomentose with long, one-celled hairs and/or long, curled, septate hairs along veins or glabrate;
adaxial faces sparsely hairy or glabrate.
2–30 cm, unwinged distally or throughout, finely tomentose.
spiny-winged to near apex or throughout, to 4 cm.
hemispheric, 20–60 mm × 20–70 mm.
± spheric, 12–17 × 12–17 mm.
purple, 15–28 mm, lobes 2.5–3 times longer than throat.
purple or ± white, 11–16 mm, lobes ca. 3.5 times length of throat.
lanceolate to ovate, outer and middle with appressed bases 2–4 mm wide and spreading to reflexed, appendages 2–7 mm wide, proximally glabrous or ± tomentose, distally glabrous to minutely scabridulous, spine tips 1–4 mm, inner phyllaries with unarmed, straight or twisted tips.
narrowly lanceolate, outer and middle with appressed bases ca. 1 mm wide and appressed to spreading appendages 0.5–1 mm wide, spine tips 1–1.5 mm, inner with unarmed, straight tips.
borne singly or in corymbiform arrays, sometimes a few axillary, at least terminal head usually conspicuously pedunculate, often nodding, 20–40 mm.
borne singly or in groups of 2–5, 15–18 mm.
golden to brown, 4–5 mm;
pappus bristles 13–25 mm.
light brown to gray-brown, 2.5–3.8 mm;
pappus bristles 11–13 mm.
= 16.
= 16 (Sweden).
Carduus nutans
Carduus crispus
Although reported from Connecticut, Delaware, Indiana, Massachusetts, Michigan, New Hampshire, Ohio, and Rhode Island, I have seen no specimens of Carduus nutans from those places.
Carduus nutans is part of a variable complex that has been treated as one to several species or as a single species with several subspecies or varieties. The New World plants apparently represent multiple introductions, probably representing more than one of these taxa. Various intermediates are evident, and many specimens cannot be reliably assigned. Insufficient evidence exists to reliably apply the names of the various segregate entities to North American material. In a biosystematic study, two subspecies of C. nutans were differentiated in Canada (A. M. Desrochers et al. 1988). Subspecies nutans was characterized as having arachnoid phyllaries with the terminal appendage only slightly wider than the appressed phyllary base, moderately to densely pubescent leaf bases, and a head diameter of 1.5–3.5 cm. Subspecies leiphyllus in contrast has glabrous phyllaries with the terminal appendage definitely wider than the base, glabrous or slightly pubescent bases, and heads 1.8–7 cm in diameter. Subspecies nutans was distributed in eastern Canada from Newfoundland to southern Ontario and subsp. leiocephalus from Ontario to British Columbia. Whether the results of the study (Desrochers et al.) are applicable to all the populations of musk thistles occurring in the United States has not been determined.
Hybrids between Carduus acanthoides and C. nutans (C. ×orthocephalus Wallroth) have been documented from Ontario and Wisconsin and probably occur at other sites where the parental taxa co-occur.
Nodding thistle is one of the most serious weeds in North America. It is unpalatable to wildlife and livestock and often forms dense, impenetrable stands in pastures and rangelands. It readily colonizes disturbed sites in many different habitats. A single large terminal head can produce as many as 1200 cypselae. Efforts to control musk thistle infestations with Rhinocyllus conicus, a European seed head weevil, have met with some success, but concerns have been raised because this parasite also attacks native Cirsium species.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Canadian distributions above follow R. J. Moore and C. Frankton (1974); I have not seen those specimens. Carduus crispus has been reported also from Arkansas, Connecticut, Iowa, Illinois, Maine, Maryland, Massachusetts, Missouri, New York, North Dakota, Ohio, Rhode Island, Vermont, Virginia, and West Virginia; I have not seen specimens from those states.
Two subspecies of Carduus crispus have been recognized (S. M. A. Kazmi 1964); those are not differentiated here.
Carduus crispus closely resembles the much more common C. acanthoides. Some published records of C. crispus are probably C. acanthoides. Although the degree of spininess and tough versus brittle stems were used as key characters (A. Cronquist 1980; H. A. Gleason and A. Cronquist 1991) to differentiate the two taxa, both characters are subjective, and the second is impractical with dry material.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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