1	"Lower leaf surface glabrous or with multicellular hairs mostly or solely along midrib and main veins; involucre at least as wide as long"	2
1	"Whole of lower leaf surface densely arachnoid-tomentose; involucre longer than wide"	4
2	"Capitula sessile, erect, 10–16 mm diameter; corolla 15–18 mm long; pappus 11–14 mm long"	"Carduus acanthoides"
2	"Capitula pedunculate, nodding when mature, 20–60 mm diam.; corolla 19–26 mm long; pappus 15–23 mm long"	3
3	"Stems and leaves sparsely to moderately pubescent; involucral bracts with arachnoid hairs"	"Carduus nutans"
3	"Stems and leaves glabrous; involucral bracts glabrous"	"Carduus thoermeri"
4	"Capitula in clusters of 1–4; stems with narrow wings, almost lacking below inflorescence; median involucral bracts sparsely to conspicuously arachnoid, without scarious margins; corollas mostly longer than involucral bracts"	"Carduus pycnocephalus"
4	"Capitula in clusters of 3–10; stems with broad wings, extending up to base of inflorescence; median involucral bracts sparsely arachnoid or glabrous, with scarious margins; corollas mostly shorter than involucral bracts"	"Carduus tenuiflorus"