Nodding Plumeless Thistle (Carduus nutans)

Taxonomy

Domain	Eukarya
Kingdom	Plantae
Phylum	Magnoliophyta
Class	Magnoliopsida
Superorder	Asteranae
Order	Asterales
Family	Asteraceae
Subfamily	Carduoideae
Tribe	Cardueae
Subtribe	Carduinae
Genus	Carduus

Scientific Name

Carduus nutans

Scientific Name Synonyms

Carduus nutans nutans

Carduus macrolepis

Carduus macrocephalus

Common Name

musk thistle, nodding thistle

Miller, J.H., E.B, Chambliss, N.J. Loewenstein. 2010. A Field Guide for the Identification of Invasive Plants in Southern Forests. General Technical Report SRS-119. Asheville, NC. United States Department of Agriculture, Forest Service. 126 p.

Plant

A variable biennial or annual herb characterized by sharp spines on leaves, branching stems, and bracts surrounding lavender flowers that sometimes nod to the side (thus the common name). Leafy rosettes first appear in either spring or fall, start forming a deep, hollow taproot (no rhizomes) and bolt within 6 months to 6 feet (2 m) high with midplant branches topped by 1 (to a few) composite flower heads that yield thousands of plumed seeds per plant. The plumes blow away on most, leaving the seed in the head (thus the common name “plumeless”). Spring seedlings can produce seeds in the same year while the more common fall rosettes overwinter to produce flower stalks the next spring.

Stem

Round, fleshy, often covered with dense, white, weblike hairs (or not) towards the tops along with scattered spiny bracts, while spiny leafy ridges extend downward along the more stout and erect branched stems towards the leafy base.

Leaves

Seedling leaves in a rosette are oval to oblong with whitish midveins and margined with tiny spines. Larger rosettes follow with thick, dandelionlike leaves up to 15 inches (40 cm) long, coarsely toothed with whitish, sharp spines extending from each vein. Dark green, hairless, and glossy above with a wide whitish midvein, and lighter green beneath. Similar sized leaves spiral out from the stems and decrease in size upward, becoming leafy spiny bracts scattered below the flower heads.

Flowers

May to September. Each branch topped by a domed flower bud covered with concentric rows of white spine-tipped bracts that part back and arch downward to form a spiny skirt for a showy pinkish to purplish-lavender thistle flower, 1.5 to 3 inches (4 to 8 cm) wide. Each composed of hundreds of tiny perfect flowers, sometimes nodding to the side, and the tallest on a plant being the largest with the most flowers.

Fruit and seeds

June to October. Tightly packed seed heads of tapered nutlets (achenes), each 0.1 to 0.2 inch (3 to 5 mm) long topped by whitish bristles that frequently blow away without the seed. Upwards to 120,000 seeds produced by a single plant in a year.

Ecology

Rosettes have buds that produce sprouts when disturbed. Flowers pollinated by insects, most being cross-pollinated, but self-pollination does occur. Seeds are equipped for dispersal by wind, water, livestock, human activity, and ants, with viability exceeding 10 years in the soil. Most seeds dispersed near the plant and with seed head fall.

Resembles

Resembles the invasive bull thistle [Cirsium vulgare (Savi.) Ten.] that has hairs on the upper leaf surfaces and the perennial Canada thistle [C. arvense (L.) Scop.] that has rhizomes, does not appear in the rosette form and only the most outer flower/seed head bracts are spiny.

History and use

Introduced from Southern Europe in the early 1900s as an ornamental.

Distribution

Found throughout the region except FL.

Management strategies

• Bag and dispose of plants and seed heads in a dumpster or burn.
• Treat when new plants are young to prevent seed formation.
• Pull, cut, and treat when seeds are not present.
• Minimize disturbance within miles of where this plant occurs, and anticipate wider occupation when plants are present before disturbance.
• Manually pull when soil is moist to ensure removal of all roots.

Recommended control procedures

• Thoroughly wet all leaves with one of the following herbicides in water with a surfactant: Transline* † as a 0.5-percent solution (2 ounces per 3-gallon mix) applied during the rosette stage or prior to flowering, Garlon 3A or a glyphosate herbicide as a 2-percent solution (8 ounces per 3-gallon mix), Milestone VM* as a 0.5-percent solution (2 ounces per 3-gallon mix), or Overdrive®* as a 0.8-percent solution (0.3 ounce per 3 gallon mix) applied at the rosette growth stage.

* Nontarget plants may be killed or injured by root uptake.

† Transline controls a narrow spectrum of plant species.

Images

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