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