Musk Thistle - Carduus nutans
Nodding Plumeless-thistle, Nodding Thistle, Nodding Thistle
Stems 30–150 cm. Herbage glabrate to villous. Leaves: basal wing-petiolate; blades oblanceolate, pinnately lobed, 6–20 cm long; cauline sessile, reduced upward. Inflorescence of solitary, sometimes nodding heads on spiny peduncles 2–30 cm long. Involucres 2–4 cm high; phyllaries lanceolate, outer reflexed; inner unarmed. Disk corollas 15–25 mm long. Achenes 4–5 mm long (Lesica 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
, 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.Native versus Exotic
(Source: Parkinson and Mangold 2015)
* Native thistles tend to have involucral bracts adhere to the flower head for most of their length (except for the spine).
* Native thistles tend to grow scattered across a habitat, spreading slowly with disturbance, and contribute to plant diversity.
* Exotic thistles grow quickly with disturbance, form dense patches that interferes with access, and through competition often reduces plant diversity.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.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.
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).