Spiny Plumeless-thistle - Carduus acanthoides
Other Names:
Plumeless Thistle, Welted Thistle
Stems 30–150 cm. Herbage sparsely villous on midveins. Leaves: basal wing-petiolate; blades oblanceolate, deeply pinnately lobed, 10–20 cm long; cauline sessile, reduced upward. Inflorescence with several erect heads on spiny stems; peduncles 1–2 cm long. Involucres 14–20 mm high; phyllaries linear-lanceolate, appressed, the outer spine-tipped, inner purple, long-attenuate. Disk corollas 12–20 mm long. Achenes 2–3 mm long (
Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).
On first-glance thistles can look similar, but upon closer inspection differences become apparent.
Thistles belong to the genera of
Cirsium,
Carduus, and
Onopordum. They are separated by:
Cirsium* Feathery (plumose) pappus, which have fine, long hairs on each side of the main bristle.
* Receptacle of flower head has bristles. Look between florets within a flower head to find them.
Carduus* Capillary pappus, which are minutely barbed, narrow bristles.
* Receptacle of flower head has bristles. Look between florets within a flower head to find them.
Onopordum* Receptacle of flower head has no bristles. Look between florets within a flower head to find nothing.
* Entire lengths of stems have spiny wings.
* Foliage is silvery gray.
Spiny Plumeless Thistle -
Carduus acanthoides, exotic and undesirable
* Flower heads are several per stem and have involucres are less than 2 cm tall.
* Flower heads have involucral bracts that are narrowly triangular (less than 2mm wide), have smooth margins, and a short spine-tip.
* Heads nod as flowers mature.
Musk Thistle -
Carduus nutans, exotic and undesirable
* Flower heads are mostly solitary and have involucres of 2-4 cm tall.
* Flower heads have involucral bracts that are broadly triangular (more than 2mm wide), have smooth margins, and a short spine-tip.
* Heads nod as flowers mature.
POLLINATORS The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap:
Bombus vagans,
Bombus auricomus,
Bombus borealis,
Bombus fervidus,
Bombus pensylvanicus,
Bombus bimaculatus,
Bombus griseocollis, and
Bombus impatiens (Thorp et al. 1983, Colla and Dumesh 2010, Williams et al. 2014, Tripoldi and Szalanski 2015).
