Comparison of spiny-leaved thistles:

Comparison of spiny-leaved thistles: flowers pink, purple, or white, except where noted

stem wings phyllary margins receptacle chaff pappus fruit attachment other

Carduus spp.

musk, giant plumeless, Italian, & slenderflower thistles

conspicuous

(to ~ 1 cm wide)
smooth dense bristles soft minutely barbed bristles, fused at base; deciduous basal, slightly angled Italian thistle leaves sometimes faintly mottled white

Cirsium spp.

bull, Canada, yellowspine, & wavyleaf thistles
conspicuous (to 1 cm wide; bull thistle), none (Canada thistle), or inconspicuous smooth dense bristles soft feathery bristles, fused at base; deciduous basal, slightly angled

Onopordum spp.

Scotch, Illyrian, & Taurian thistles
conspicuous (mostly 1-4 cm wide) smooth membranous extensions around pits +/- firm, minutely barbed bristles, fused at base, deciduous basal receptacles deeply pitted & honeycomb-like; fruits transversely wrinkled

Cynara cardunculus

artichoke thistle
none smooth dense bristles long, stiff, feathery bristles, fused at base; deciduous basal basal leaves often compound & very large; receptacle fleshy

Silybum marianum

milk thistle
none spiny-toothed dense bristles soft, minutely barbed bristles, fused at base; deciduous basal, slightly angled leaves bright green & mottled white

Carthamus spp.

whitestem, smooth, & woolly distaff thistles
none outer leaf-like, spiny pinnate-lobed narrow scales 0 or many unequal scales in several series; persistent lateral notch near base smooth & woolly distaff thistles flowers yellow; fruits +/- 4-angled

Scolymus hispanicus

golden thistle
conspicuous (mostly to ~ 1 cm wide) smooth long scales enclose fruits 2-4 stiff, minutely barbed bristles; +/- deciduous basal flowers yellow, ligulate; sap milky

Cnicus benedictus

blessed thistle
none or inconspicuous outer smooth; inner with long, pinnate- branched spines at tips dense bristles ~ 20 stiff bristles in 2 series, outer long, inner short; persistent lateral notch near base flowers yellow; heads leafy; fruits cylindrical, with ~ 20 prominent ribs & pale crown-like teeth on apical rim

	stem wings	phyllary margins	receptacle chaff	pappus	fruit attachment	other
*Carduus* spp. musk, giant plumeless, Italian, & slenderflower thistles	conspicuous (to ~ 1 cm wide)	smooth	dense bristles	soft minutely barbed bristles, fused at base; deciduous	basal, slightly angled	Italian thistle leaves sometimes faintly mottled white
*Cirsium* spp. bull, Canada, yellowspine, & wavyleaf thistles	conspicuous (to 1 cm wide; bull thistle), none (Canada thistle), or inconspicuous	smooth	dense bristles	soft feathery bristles, fused at base; deciduous	basal, slightly angled
*Onopordum* spp. Scotch, Illyrian, & Taurian thistles	conspicuous (mostly 1-4 cm wide)	smooth	membranous extensions around pits	+/- firm, minutely barbed bristles, fused at base, deciduous	basal	receptacles deeply pitted & honeycomb-like; fruits transversely wrinkled
Cynara cardunculus artichoke thistle	none	smooth	dense bristles	long, stiff, feathery bristles, fused at base; deciduous	basal	basal leaves often compound & very large; receptacle fleshy
*Silybum marianum* milk thistle	none	spiny-toothed	dense bristles	soft, minutely barbed bristles, fused at base; deciduous	basal, slightly angled	leaves bright green & mottled white
*Carthamus* spp. whitestem, smooth, & woolly distaff thistles	none	outer leaf-like, spiny pinnate-lobed	narrow scales	0 or many unequal scales in several series; persistent	lateral notch near base	smooth & woolly distaff thistles flowers yellow; fruits +/- 4-angled
*Scolymus* *hispanicus* golden thistle	conspicuous (mostly to ~ 1 cm wide)	smooth	long scales enclose fruits	2-4 stiff, minutely barbed bristles; +/- deciduous	basal	flowers yellow, ligulate; sap milky
*Cnicus benedictus* blessed thistle	none or inconspicuous	outer smooth; inner with long, pinnate- branched spines at tips	dense bristles	~ 20 stiff bristles in 2 series, outer long, inner short; persistent	lateral notch near base	flowers yellow; heads leafy; fruits cylindrical, with ~ 20 prominent ribs & pale crown-like teeth on apical rim