Flora of North America species comparison

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Carduus

chardon, plumeless thistle
Habit Annuals or biennials [perennials], 30–200(–400) cm, spiny, ± tomentose, sometimes glabrate.
Stems

erect, simple to much branched, (spiny-winged).
Leaves

basal and cauline;

petiolate or sessile;

blade margins spiny dentate, often 1–2-pinnately lobed, faces glabrous or hairy, eglandular.
Receptacles

flat, epaleate, bearing setiform scales (“flattened bristles”).
Florets

several–many;

corollas white to pink or purple, ± bilateral, tubes long, slender, throats short, campanulate, abruptly expanded from tubes, lobes linear;

anther bases sharply short-tailed, apical appendages oblong;

style branches: fused portions with slightly, minutely puberulent, swollen basal nodes, distally papillate or glabrous, distinct portions very short.
Phyllaries

many in 7–10+ series, linear to broadly ovate, bases appressed, margins entire, apices ascending to spreading or reflexed, acute, spine-tipped.
Heads

discoid, borne singly or 2–20 in dense clusters or corymbiform arrays. (Peduncles naked or leafy-bracteate, spiny-winged or not winged.) Involucres cylindric to spheric.
Cypselae

ovoid, slightly compressed, faces smooth, glabrous, attachment scars slightly lateral;

pappi persistent or falling in rings, of many minutely barbed, basally connate bristles or setiform, minutely barbed scales (“minutely flattened bristles”).
x

= 8, 9, 10, 11, 13.

Carduus
Distribution
from USDA
Eurasia; Africa [Introduced in North America]
[BONAP county map]
Discussion

Species ca. 90 (5 in the flora).

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Phyllary appendages 2–7 mm wide, usually wider than appressed bases; peduncles often elongate, distally wingless; heads often nodding, usually borne singly or in leafy corymbiform arrays; involucres 20–70 mm diam
C. nutans
1. Phyllary appendages 0.5–1.5 mm wide, usually narrower than appressed bases; peduncles short, if present, usually winged throughout or wingless only near tip; heads erect, 1–many, often clustered at branch tips; involucres 7–30 mm diam
→ 2
2. Involucres spheric or hemispheric
→ 3
2. Involucres cylindric or narrowly ellipsoid
→ 4
3. Corollas 13–20 mm; heads 18–25 mm; involucres 14–20 mm; abaxial leaf faces glabrate except for long, curled, septate hairs along veins
C. acanthoides
3. Corollas 11–16 mm; heads 15–18 mm; involucres 12–17 mm; abaxial leaf faces sparsely to densely tomentose with fine, nonseptate hairs and often with curled, septate hairs along veins as well
C. crispus
4. Heads 1–5 at ends of branches; phyllaries not scarious-margined, ± persistently tomentose, distally scabrous on margins and faces
C. pycnocephalus
4. Heads 5–20 at ends of branches; phyllaries scarious-margined, glabrous or spar- ingly tomentose, distally ciliolate or glabrous
C. tenuiflorus
Source FNA vol. 19, p. 91. Author: David J. Keil.
Parent taxa Asteraceae > tribe Cardueae
Subordinate taxa
C. acanthoides, C. crispus, C. nutans, C. pycnocephalus, C. tenuiflorus
Name authority Linnaeus: Sp. Pl. 2: 820. (1753): Gen. Pl. ed. 5, 358. (1754)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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