Carduus thistles:

	flower head shape & arrangement	flower head width	flower stalk length	phyllary width & hairs	other
musk thistle Carduus nutans	(hemi-) spherical solitary, often nodding	2-7 cm	> 2 cm	> 2 mm short-hairy to glabrous
giant plumeless thistle Carduus acanthoides	(hemi-) spherical solitary or clustered	1-3 cm	< 2 cm	< 2 mm loosely woolly to glabrous
Italian thistle Carduus pycnocephalus	cylindrical or elliptical mostly 2-5-clustered	~ 1-2 cm	< 2 cm	< 2 mm woolly at bases	lower leaves mostly 4-10-lobed; phyllary tips sandpapery to touch (scabrous)
slenderflower thistle Carduus tenuiflorus	cylindrical or elliptical mostly 5-20-clustered	~ 1-2 cm	< 2 cm	< 2 mm glabrous to sparsely woolly	lower leaves mostly 12-20-lobed; phyllary margins narrowly membranous