Your search found 12 image(s) of involucral bracts of Thistles.
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Bull Thistle,
Cirsium vulgare
Involucral bracts narrowly pointed, rigid, not sticky, per Wildflowers in the Field and Forest.
Common Yellow Thistle,
Cirsium horridulum var. horridulum
Flower heads more or less enclosed by an outer whorl of spiny leaf-like bracts, per Vascular Flora of the Carolinas.
Field Thistle,
Cirsium discolor
Involucres, from 1-1.5" long, have middle & outer bracts tipped with a spine, per Wildflowers of Tennessee.
Tall Thistle,
Cirsium altissimum
Involucres 2-3.5cm long, 2-3.5cm broad, weakly arachnose, per Vascular Flora of the Carolinas.
Carolina Thistle,
Cirsium carolinianum
Involucres 0.6-0.8" high, bracts appressed, only outer with short spines, per Wildflowers of Tennessee, the Ohio Valley, and the Southern Appalachians.
Coastal Tall Thistle,
Cirsium nuttallii
Involucres subtend a mass of pale pink to nearly cream disk flowers, per Atlantic Coastal Plain Wildflowers.
Sandhill Thistle,
Cirsium repandum
Heads 1-5, rarely more, corymbose. Involucres 2.5-3.3cm long, arachnose, per Vascular Flora of the Carolinas.
Swamp Thistle,
Cirsium muticum
Involucres 0.8-1.4" with sticky hairy bracts that usually don't have spines, per Wildflowers of Tennessee.
Canada Thistle,
Cirsium arvense
Involucres are smooth or, at most, have minute prickles on outer bracts, per Wildflowers of the Southern Mountains.
Nodding Thistle,
Carduus nutans
A nodding head with broad, purplish reflexed involucral bracts, per Wildflowers of the Southern Mountains.
Plumeless Thistle,
Carduus acanthoides ssp. acanthoides
Involucres arachnose. Outer involucral bracts erect, inner bracts soft, per Vascular Flora of the Carolinas.